fix: apply-template auto-solves + frontend reloads via activateProject

Two changes to close the UX hole m hit on slice 6 — Apply Template
appeared to do nothing because (a) the canvas wasn't refreshed cleanly
and (b) the cables hadn't been computed yet.

Backend (internal/server/solver.go applyTemplate handler):
- After ApplyTemplate succeeds, run Solve(false) inside the same
  request. Combined response shape:
    { template_apply: <ApplyTemplateResult>, solve: <SolveResult> }
- Opt out with ?solve=0 for power-users who want to inspect the
  seeded devices/requirements before the solver runs. Response in that
  case is { template_apply: ... } only.
- If Solve fails after a successful apply, return
  { template_apply, solve_error: "..." } so the frontend can recover
  (devices are still there; m can hit Solve manually).

Frontend (web/static/main.js apply-template modal submit):
- Replaced the bare re-snapshot with a call to activateProject(pid).
  That's the canonical project-load path — it re-hydrates ALL
  collections (frames, devices, ports, io_markers, cables, bundles,
  requirements, cable_types, device_types), clears state.selection
  so a stale pre-apply selection can't linger, and routes through the
  same render() the URL-state hydration uses on initial page load.
- The slice-6 inlined re-snapshot missed the device_types refresh +
  selection reset, which I suspect was what made the canvas look
  stuck — render()ing with state.selection.kind="cable_type" or
  "requirement" pointing at a not-yet-loaded row.

Hand-test (local): Living Room + auto-solve produces 4 devices + 3
requirements + 3 cables; ?solve=0 leaves cables empty. Snapshot
includes the cables on auto-solve path.

CLAUDE.md

@@ -2,11 +2,21 @@
 
 ## Project Overview
 
-Cable-management **framework** for m's setup. Each cable-managed environment
-(LOFT, OFFICE, …) is a separate **mCables project**, and each project is
-backed by exactly one Excalidraw drawing. The framework provides a visual
-web interface backed by a Go HTTP API and SQLite, plus an export pipeline
-that writes `.excalidraw` files via mExDraw.
+Cable-management **framework + solver** for m's setup. m declares his
+**devices** and the **connection requirements** between them ("NAS must
+connect to Switch via RJ45"). mCables runs a solver that emits the cable
+plan + bundle recommendations. mCables is a **schematic**, not a
+physical-routing tool — cables are straight lines between endpoints; the
+"maximum bundling" objective is satisfied by the endpoint-pair rule
+(when two or more cables share the same A↔B endpoint pair, group them
+into one bundle). The visual editor is still there for tweaking the
+plan, but the solver is the headline.
+
+Each cable-managed environment (LOFT, OFFICE, …) is a separate
+**mCables project**, and each project is backed by exactly one Excalidraw
+drawing. The framework provides a visual web interface backed by a Go
+HTTP API and SQLite, plus an export pipeline that writes `.excalidraw`
+files via mExDraw.
 
 **Memory group_id:** `mcables`
 
@@ -19,13 +29,25 @@ interface. The backend serves the UI and the API; there is no
 - A reusable framework for tracking devices, ports, cables, cable types,
   bundles, frames — **scoped per project** (LOFT and OFFICE are separate
   projects, each a separate drawing).
-- A visual editor in the browser: switch projects, add frames/devices/ports,
-  click ports to wire up cables, pick cable types from a per-project legend.
-- A one-way export from the DB to the corresponding `.excalidraw` drawing
-  on `mxdrw.msbls.de` whenever m clicks Export — DB is authoritative,
-  Excalidraw is the projection.
-- Bundle detection: parallel cables along the same path within a project
-  get grouped + colour-bundled in the diagram.
+- A **solver** that, given the project's devices + connection
+  requirements, emits the cable plan + bundle recommendations.
+  Objective: maximum bundling via the endpoint-pair rule (schematic
+  only — no path/trunk/cable-tray modelling).
+- A **hybrid device-type catalog**: 14 built-in types (NAS, PC, Mac,
+  Notebook, TV, Soundbar, Switch, fritz, ChromeCast, SteamLink,
+  IOx-3/6/8, Screen, Keyboard, Mouse) with default port profiles,
+  extensible per project. Picking a type on device-create seeds the
+  device's ports automatically; m overrides per instance.
+- **Setup templates** for bootstrapping a project from blank to
+  solver-ready: built-ins 'Living Room', 'Home Office', 'Server Rack'
+  stamp their device-types + connection requirements in one transaction.
+- A visual editor for switching projects, adding frames/devices,
+  declaring requirements, running the solver, and tweaking the
+  resulting plan. Unmet requirements get a one-click quick-fix
+  ("+ Add <type> port to <device> and re-solve").
+- A one-way export from the DB to the corresponding `.excalidraw`
+  drawing on `mxdrw.msbls.de` whenever m clicks Export — DB is
+  authoritative, Excalidraw is the projection.
 
 ## Architecture
 
@@ -45,16 +67,31 @@ interface. The backend serves the UI and the API; there is no
 - **Frames** sub-divide a project (LOFT has `desk`, `rack`, `media`;
   OFFICE has `desk`, `server`). Frames are not projects — they're zones
   within one drawing.
-- Every device, port, cable, IO marker, and bundle is **project-scoped**
-  (`project_id` denormalised onto every row, with `ON DELETE CASCADE` from
-  `projects`). `UNIQUE (project_id, devices.name)` — no two devices in
-  one project share a name.
+- Every device, port, cable, IO marker, bundle, and **connection
+  requirement** is **project-scoped** (`project_id` denormalised onto
+  every row, with `ON DELETE CASCADE` from `projects`).
+  `UNIQUE (project_id, devices.name)` — no two devices in one project
+  share a name.
 - **Cable types are global.** A single shared `cable_types` table —
   no `project_id`. The five defaults (Power/USB/HDMI/DP/RJ45) are seeded
   by migration 001 once, not per project. Renaming or recolouring a type
   affects every project's legend immediately.
+- **Device types are hybrid.** `device_types` is one global table with
+  `project_id` NULL for the 11 built-in catalog rows (seeded by
+  migration 002) and `project_id = current` for project-custom types.
+  Each `device_type` carries a `device_type_ports` profile that seeds
+  `ports` rows when a device of that type is created. m can extend the
+  catalog per project; built-ins are read-only from the API.
+- **Connection requirements** (`connection_requirements` table) are the
+  solver's input. m declares "from_device ↔ to_device, preferred cable
+  type, must_connect"; the solver assigns ports and emits cables.
 - **Project deletion guardrail.** `DELETE /api/projects/:pid` requires
   `?confirm=<name>` matching the project's current name. 400 otherwise.
+- **Solver-owned vs. user-owned cables.** `cables.auto = 1` = created by
+  the solver and replaceable on re-solve. `auto = 0` = hand-drawn by m,
+  left alone by the solver. PATCHing endpoint or type of an auto cable
+  promotes it to manual (explicit "Promote to manual" button in the
+  inspector, per design v4 §5b.3).
 
 ## Branch Strategy
 
@@ -137,12 +174,14 @@ Legend colours (global, seeded once by migration 001):
 
 ## Worker Preferences
 
-- **First shift = inventor** (design pass): conventions, schema, API,
-  export pipeline, mDock deploy plan, UI flows, slices. Output:
-  `docs/design.md` + open questions for m.
-- **Second shift = coder** (after m's go on the design): bootstrap repo
-  skeleton (Go module, SQLite migrations, server, exporter, frontend
-  scaffold). Take slices 1–4 first (project CRUD, frames/devices, ports
-  and cables, IO + cable-type editing); slice 5 (Excalidraw export) closes
-  the round-trip.
-- Use **Sonnet** for both — greenfield, structure matters more than depth.
+- **Inventor shifts** (design passes): conventions, schema, API, export
+  pipeline, mDock deploy plan, UI flows, slices. Output: `docs/design.md`
+  + open questions for m. v1–v4 are versioned in the doc's header callout.
+- **Coder shifts** (after m's go on a design version): build to the
+  current design.md. Current state: slice 1 (project CRUD + global
+  cable_types) and slice 2 (frames + devices + drag) are merged; design
+  v4 reshapes slices 3+ (IO + cable-type editing → device-type catalog →
+  device-type manage → connection-requirements UI → solver → manual
+  port/cable draw → export). See `docs/design.md` §8 for the current
+  sequence.
+- Use **Sonnet** for both — structure matters more than depth.

docs/design.md

@@ -1,36 +1,95 @@
-# mCables — Design v3
+# mCables — Design v4.1
 
-Cable-management **framework** for m's setup. Inventor shift 1 design,
-revised after m's round-4 answers (2026-05-15) — for m's review.
+Cable-management **framework + solver** for m's setup. Inventor shift 1
+design, revised through v2 (rescope to multi-project framework), v3
+(global cable_types + guardrails), v4 (solver-as-core), and now
+**v4.1 — six locked answers from m's v4 review**.
+
+> **What changed in v4.1** (tight pass on v4)
+> 1. **mCables is a schematic, not a physical-routing tool.** Cables are
+>    straight lines between endpoints; the solver and the renderer do not
+>    care about paths, trunks, frame edges, or cable-tray polylines.
+>    "Maximum bundling" reduces to the v3 rule: **≥2 cables between the
+>    same endpoint pair → bundle them.** All path-routing language has
+>    been stripped from §5b.1, §5b.2, §7, §8, §9.
+> 2. **Solver fires on the Solve button (v0).** Live-solve stays in §8
+>    slices 9+ as an opt-in toggle.
+> 3. **Unmet-requirement quick-fix**: when the solver returns
+>    `unsatisfied[]`, the device inspector renders a red badge per unmet
+>    requirement with a single button — **"+ Add <type> port to
+>    <device> and re-solve"** — that POSTs a new port to the
+>    device AND immediately re-runs `POST /api/projects/:pid/solve` in
+>    the same UI action. See §5b.4 + §7 inspector-states.
+> 4. **Setup templates fold INTO v4.1.** New tables `setup_templates`,
+>    `setup_template_devices`, `setup_template_requirements` in
+>    migration 004 + 3 built-in templates ('Living Room', 'Home Office',
+>    'Server Rack'). New endpoints `GET /api/setup-templates` and
+>    `POST /api/projects/:pid/apply-template`. UI: a "Templates" panel
+>    in the New Project flow + an "Apply template" action on an empty
+>    project. See new §2.4 + slice 6 fold-in below.
+> 5. **Catalog distribution: SQL seed** in migration 002 (no change).
+> 6. **Promote to manual: explicit button** on the cable inspector
+>    (no change).
 
 Sources: the live `Cable-Management.excalidraw` on mxdrw.msbls.de (used as
-the *visual-grammar reference*, not as a bootstrap import target),
-`mai-memory` (`mcables`, `m`), and a live survey of mDock services for the
-deploy conventions (§10).
+the *visual-grammar reference*, not a bootstrap import target),
+`mai-memory` (`mcables`, `m`), and the live mDock services for deploy
+conventions (§10). v4 driven by m's product-vision clarification:
 
-> **What changed in v3** (mechanical deltas on top of v2)
-> - `cable_types` is now a **global** table — one set shared across all
->   projects. Migration 001 seeds the 5 defaults once. `POST /api/projects`
->   no longer seeds types. API moved to top-level `/api/cable-types`.
->   Renaming/recolouring a type affects every project.
-> - `devices` gains `UNIQUE (project_id, name)` — no two devices in the
->   same project can share a name.
-> - `projects.drawing_name` is auto-filled `<name>.excalidraw` server-side
->   when omitted on POST; editable via PATCH.
-> - `DELETE /api/projects/:pid` requires `?confirm=<name>` query param;
->   server checks it matches the project's current name. 400 otherwise.
+> "we provide a cable manager — I say what devices we have, the app tells
+> me how to bundle cables and how the most efficient connection looks like"
+
+mCables shifts from a manual draw-and-click editor to a **solver** that
+takes a list of devices + the connections m needs and emits the cable
+plan + bundle recommendations. The manual editor stays (it's the only way
+to inspect + tweak the plan) but is no longer the primary surface.
+
+> **What changed in v4** (new mental model on top of v3 mechanics)
+> - **Hybrid device-type catalog** (§2.1, §3.1). A built-in `device_types`
+>   table seeds common devices (NAS, PC, Mac, TV, Soundbar, Switch, fritz,
+>   ChromeCast, SteamLink, IOx-3/6/8, Notebook, …) with default port
+>   profiles (`device_type_ports` rows: cable_type + count + label).
+>   Adding a device → pick a type → ports auto-seed. m can override per
+>   instance (this PC has 3 USB, not 2). Catalog is extendable per project.
+> - **`connection_requirements` table** (§2.2). m declares "NAS must
+>   connect to Switch via RJ45" once. Many per device. The solver consumes
+>   these.
+> - **`POST /api/projects/:pid/solve` endpoint** (§3.2). Reads devices +
+>   their ports + connection_requirements + frame positions, emits a diff
+>   of `cables` + `bundles`. Two modes: `?preview=1` returns the diff
+>   without applying; default applies.
+> - **Solver objective: maximum bundling** (§5b.1). Schematic only: when
+>   two or more cables share the same endpoint pair, group them into one
+>   bundle. No path or trunk geometry — mCables is a wiring schematic,
+>   not a routing tool. v4.1 strips all path/trunk language from the v4
+>   draft.
+> - **UI: device-type dropdown** on device-create, **Connection
+>   Requirements** left panel, **Solve** button next to Export. Inspector
+>   shows type + ports + unmet requirements (selected device) or the
+>   driving requirement + bundle (selected cable).
+> - **Slices reshape** (§8). Catalog seeding lands early (slice 1.5); the
+>   solver MVP and connection-requirements UI move ahead of the
+>   bundle-rendering polish.
 >
-> **What carried over from v2**
-> - mCables is a framework: top-level `projects` table; LOFT and OFFICE
->   are separate projects, each backed by one drawing.
-> - No runtime importer. The seed drawing is reference material only.
->   `/api/sync/import` is out of MVP; only `POST .../sync/export` ships.
-> - IO diamonds are wall-outlet terminators (type=Power by convention,
->   not enforced in schema). UI soft-warns on non-Power cables to an IO.
-> - No cable inventory metadata. Purely visual structure for v0.
-> - DB at `./data/mcables.db` (project-local, gitignored).
-> - Deploy: raw docker / docker-compose on mDock (not Dokploy).
-> - Bind `0.0.0.0:7777` on the LAN, no auth.
+> **What carried over from v3 (unchanged in v4)**
+> - mCables is a framework: top-level `projects`, each backed by one
+>   `.excalidraw` drawing. `UNIQUE(projects.name)`.
+> - `cable_types` is global. Migration 001 seeds Power/USB/HDMI/DP/RJ45.
+> - `devices` UNIQUE(project_id, name); `frame_id` nullable; FrameRef
+>   tri-state on PATCH.
+> - IO diamonds = wall-outlet terminators (type=Power by convention).
+> - `projects.drawing_name` auto-defaults to `<name>.excalidraw`.
+> - `DELETE /api/projects/:pid?confirm=<name>` guardrail.
+> - No cable inventory metadata; visual + connectivity structure only.
+> - DB at `./data/mcables.db` (gitignored). Bind `0.0.0.0:7777` LAN, no auth.
+> - Deploy on mDock under `/home/m/stacks/mcables/`, raw docker-compose.
+>
+> **What's superseded in v4**
+> - The "manual draw-a-cable port-to-port" flow from v3 §7 is *kept* as a
+>   tweak path on the solver output, but is no longer the *primary* device-
+>   connecting flow. The solve button is the headline action.
+> - The v3 §8 slice order changes — catalog + types-driven devices + solver
+>   come earlier; the manual-draw-cable slice slides later. See new §8.
 
 ---
 
@@ -134,6 +193,49 @@ CREATE TABLE cable_types (
     updated_at      TEXT NOT NULL DEFAULT (datetime('now'))
 );
 
+-- v4 — device-type catalog. Seeded built-in types live globally (so
+-- multiple projects share the "NAS" definition without duplication).
+-- Per-project custom types are also allowed (project_id non-null for those).
+-- Renaming a built-in type doesn't propagate retroactively to existing
+-- devices that already had their ports seeded — they own their port set
+-- from the moment they were created.
+CREATE TABLE device_types (
+    id              INTEGER PRIMARY KEY,
+    project_id      INTEGER REFERENCES projects(id) ON DELETE CASCADE,
+                                                  -- NULL = built-in (shared), non-null = project-custom
+    name            TEXT NOT NULL,                -- "NAS", "PC", "TV", "Switch", "IOx-8", "Custom-Foo"
+    kind            TEXT NOT NULL DEFAULT 'generic',
+                                                  -- coarse category for UI grouping: 'storage', 'compute',
+                                                  -- 'display', 'audio', 'network', 'hub', 'accessory',
+                                                  -- 'generic'
+    icon            TEXT,                         -- emoji or short symbol (🖥, 📺, 🔊, 📡) — UI hint
+    description     TEXT NOT NULL DEFAULT '',
+    built_in        INTEGER NOT NULL DEFAULT 0,   -- 1 for migration-seeded rows, 0 for user-created
+    created_at      TEXT NOT NULL DEFAULT (datetime('now')),
+    updated_at      TEXT NOT NULL DEFAULT (datetime('now')),
+    UNIQUE (project_id, name)                     -- two projects can both have a custom "Foo";
+                                                  -- built-ins (project_id NULL) get UNIQUE on name globally
+);
+CREATE INDEX device_types_project_idx ON device_types(project_id);
+
+-- v4 — port profile per device type. "NAS has 1 Power + 1 RJ45" is two
+-- rows; "PC has 1 Power + 1 RJ45 + 1 HDMI + 2 USB" is four rows.
+-- When a device is created with type_id=X, the seeder inserts `count`
+-- rows into the `ports` table for each device_type_ports entry,
+-- numbering label as "<label_prefix> N" if count > 1.
+CREATE TABLE device_type_ports (
+    id              INTEGER PRIMARY KEY,
+    device_type_id  INTEGER NOT NULL REFERENCES device_types(id) ON DELETE CASCADE,
+    cable_type_id   INTEGER NOT NULL REFERENCES cable_types(id)  ON DELETE RESTRICT,
+    label_prefix    TEXT NOT NULL DEFAULT '',     -- "HDMI", "USB", "Power" — UI label root
+    count           INTEGER NOT NULL DEFAULT 1 CHECK (count >= 1),
+    -- Position hint: the seeder lays ports along the device edge using
+    -- these biases (0..1 along the edge fraction). NULL = even spread.
+    edge            TEXT NOT NULL DEFAULT 'bottom' CHECK (edge IN ('top','bottom','left','right')),
+    sort_order      INTEGER NOT NULL DEFAULT 0
+);
+CREATE INDEX device_type_ports_type_idx ON device_type_ports(device_type_id);
+
 -- A frame is a named container *inside* a project: 'desk', 'rack', 'media'.
 CREATE TABLE frames (
     id              INTEGER PRIMARY KEY,
@@ -154,10 +256,19 @@ CREATE INDEX frames_project_idx ON frames(project_id);
 -- Devices live in a frame (and transitively in a project).
 -- Stored project_id is denormalised for cheap project-scoped queries; FK
 -- to frame_id is the structural truth. Both are kept consistent in code.
+--
+-- v4 — type_id (nullable) lets a device inherit its port profile from
+-- a `device_types` row. Once ports are seeded the device "owns" them;
+-- changing/clearing type_id later does not retroactively re-seed (m's
+-- per-instance overrides survive). Custom freeform devices (no template)
+-- keep type_id NULL — that's the v3 "just a rectangle" device.
 CREATE TABLE devices (
     id              INTEGER PRIMARY KEY,
     project_id      INTEGER NOT NULL REFERENCES projects(id) ON DELETE CASCADE,
     frame_id        INTEGER REFERENCES frames(id) ON DELETE SET NULL,
+    type_id         INTEGER REFERENCES device_types(id) ON DELETE SET NULL,
+                                                  -- v4: nullable; SET NULL on type delete so we don't
+                                                  -- cascade-delete a device the user still wants
     name            TEXT NOT NULL,
     color           TEXT NOT NULL DEFAULT '#1e1e1e',
     x               REAL NOT NULL,
@@ -172,6 +283,7 @@ CREATE TABLE devices (
 );
 CREATE INDEX devices_project_idx ON devices(project_id);
 CREATE INDEX devices_frame_idx   ON devices(frame_id);
+CREATE INDEX devices_type_idx    ON devices(type_id);
 
 -- Ports belong to a device. x_offset/y_offset are relative to the device's
 -- top-left so ports follow when the device moves. project_id denormalised.
@@ -260,8 +372,211 @@ CREATE TABLE bundle_cables (
     PRIMARY KEY (bundle_id, cable_id)
 );
 CREATE INDEX bundle_cables_cable_idx ON bundle_cables(cable_id);
+
+-- v4 — connection_requirements: the input m gives the solver.
+-- "NAS must connect to Switch via RJ45" is one row. Many per device.
+--
+-- preferred_cable_type_id is the cable type m intends — the solver
+-- needs it to match port colours. NULL means "solver picks" (the solver
+-- will pick the unique cable_type that is compatible with both ends'
+-- available port types; if ambiguous it surfaces an error for m).
+--
+-- must_connect = 1 (default) means the solver MUST satisfy this; an
+-- unsatisfiable must_connect surfaces as a hard error in the solve
+-- result. must_connect = 0 = "nice to have, drop if you run out of
+-- ports". Used for templates that over-spec.
+--
+-- The (from_device_id, to_device_id) pair is normalised on insert so
+-- (A,B) and (B,A) are the same requirement — UNIQUE on the unordered
+-- pair + cable type prevents duplicates.
+CREATE TABLE connection_requirements (
+    id                       INTEGER PRIMARY KEY,
+    project_id               INTEGER NOT NULL REFERENCES projects(id) ON DELETE CASCADE,
+    from_device_id           INTEGER NOT NULL REFERENCES devices(id) ON DELETE CASCADE,
+    to_device_id             INTEGER NOT NULL REFERENCES devices(id) ON DELETE CASCADE,
+    preferred_cable_type_id  INTEGER REFERENCES cable_types(id) ON DELETE SET NULL,
+    must_connect             INTEGER NOT NULL DEFAULT 1 CHECK (must_connect IN (0, 1)),
+    notes                    TEXT NOT NULL DEFAULT '',
+    -- Order-normalised pair: lo = MIN(from, to), hi = MAX(from, to). Set
+    -- in code on insert; the UNIQUE then prevents (A,B,Power) AND
+    -- (B,A,Power) from coexisting. Stored alongside the m-facing
+    -- from/to so the UI doesn't have to denormalise.
+    pair_lo                  INTEGER NOT NULL,
+    pair_hi                  INTEGER NOT NULL,
+    CHECK (from_device_id != to_device_id),
+    UNIQUE (project_id, pair_lo, pair_hi, preferred_cable_type_id),
+    created_at               TEXT NOT NULL DEFAULT (datetime('now')),
+    updated_at               TEXT NOT NULL DEFAULT (datetime('now'))
+);
+CREATE INDEX conn_reqs_project_idx ON connection_requirements(project_id);
+CREATE INDEX conn_reqs_pair_idx    ON connection_requirements(project_id, pair_lo, pair_hi);
+CREATE INDEX conn_reqs_from_idx    ON connection_requirements(from_device_id);
+CREATE INDEX conn_reqs_to_idx      ON connection_requirements(to_device_id);
 ```
 
+### 2.1 Migration sequence
+
+- **001_init.sql** (v3) — projects, frames, devices (no type_id), ports,
+  cable_types (5 seeded), io_markers, cables, bundles, bundle_cables.
+- **002_device_catalog.sql** (v4) — `device_types` +
+  `device_type_ports`. Seeds the built-in catalog (§2.2). Adds
+  `devices.type_id` (`ALTER TABLE devices ADD COLUMN type_id INTEGER
+  REFERENCES device_types(id) ON DELETE SET NULL`) and the matching
+  index.
+- **003_connection_requirements.sql** (v4) — `connection_requirements`.
+  Also adds `cables.auto` (`ALTER TABLE cables ADD COLUMN auto INTEGER
+  NOT NULL DEFAULT 0`) so the solver can distinguish its rows from
+  m's hand-drawn ones (§5b.3).
+- **004_setup_templates.sql** (v4.1 NEW) — `setup_templates` +
+  `setup_template_devices` + `setup_template_requirements`. Seeds 3
+  built-in templates ('Living Room', 'Home Office', 'Server Rack').
+
+Slices 1 and 2 already shipped 001. Slice 4 lands 002; slice 5 lands
+003; slice 6 lands 004 alongside the solver MVP + templates UI.
+
+### 2.2 Built-in catalog seed (002 INSERTs)
+
+The 14 built-in types m's setup uses today, with their default port
+profiles. Stored as `(project_id NULL, built_in 1)`. v4.1 added the
+three peripheral types (Screen, Keyboard, Mouse) to support the Home
+Office setup template:
+
+| `device_types.name` | `kind` | Default ports (cable_type × count) |
+|---|---|---|
+| NAS | storage | Power × 1; RJ45 × 1 |
+| PC | compute | Power × 1; RJ45 × 1; HDMI × 1; USB × 2 |
+| Mac | compute | Power × 1; HDMI × 1; USB × 2 |
+| Notebook | compute | Power × 1; USB × 2 |
+| TV | display | Power × 1; HDMI × 2 |
+| Soundbar | audio | Power × 1; HDMI × 1 |
+| Switch | network | Power × 1; RJ45 × 5 |
+| fritz | network | Power × 1; RJ45 × 4 |
+| ChromeCast | display | Power × 1; HDMI × 1 |
+| SteamLink | compute | Power × 1; HDMI × 1; USB × 2 |
+| IOx-3 | hub | Power × 1; (3× port slots — concrete cable type per slot is set at instantiation; defaults to USB × 3 for v0) |
+| IOx-6 | hub | Power × 1; USB × 6 |
+| IOx-8 | hub | Power × 1; USB × 8 |
+| **Screen** | display | Power × 1; HDMI × 1 |
+| **Keyboard** | accessory | USB × 1 |
+| **Mouse** | accessory | USB × 1 |
+
+"Hub" devices like IOx-* have ambiguous port profiles (the seed drawing
+shows them in red because most carry Power, but they also hub USB). v0
+seeds them as USB hubs; m overrides per-instance. The catalog is editable
+in the UI (slice 4.5 — "Manage device types") so m can refine the IOx-3
+profile once and not re-override every instance.
+
+m can also add **project-custom types** at any time (UI: "+ New device
+type" inside the device-create modal) with `project_id = current`.
+
+### 2.3 Why ports are still instance-owned
+
+When m picks a type to create a device, the seeder calls `count` × INSERT
+into `ports`. From that moment on, ports are instance-level rows owned by
+that device. Deleting a port from this PC doesn't touch other PCs;
+changing a type's port profile (in slice 4.5) doesn't retroactively
+re-seed already-created devices — it only affects subsequent device
+creations.
+
+Trade-off acknowledged: m may want a "re-seed from type" action later
+(slice 5+) to wipe + reset a device's ports. Out of v0 scope; not
+blocked by the schema.
+
+### 2.4 Setup templates (v4.1 NEW)
+
+A setup template is a named recipe of "device-types to add + connection
+requirements between them" that bootstraps a project from blank to
+solver-ready in one click. m's three archetypes:
+
+| Template name | Devices | Default requirements |
+|---|---|---|
+| **Living Room** | TV, Soundbar, ChromeCast | TV ↔ Soundbar (HDMI, must); TV ↔ ChromeCast (HDMI, must) |
+| **Home Office** | PC, Screen, Keyboard, Mouse | PC ↔ Screen (HDMI, must); PC ↔ Keyboard (USB, must); PC ↔ Mouse (USB, must) |
+| **Server Rack** | NAS, Switch, fritz | NAS ↔ Switch (RJ45, must); Switch ↔ fritz (RJ45, must); fritz ↔ NAS (Power, nice) |
+
+> "Screen", "Keyboard", "Mouse" are added to the v4 built-in catalog
+> alongside the existing 11 (Screen: Power × 1 + HDMI × 1; Keyboard: USB × 1;
+> Mouse: USB × 1). Migration 002 grows to seed 14 built-ins.
+
+Schema (`004_setup_templates.sql`):
+
+```sql
+-- A named recipe: a list of device types + requirements between them.
+CREATE TABLE setup_templates (
+    id              INTEGER PRIMARY KEY,
+    name            TEXT NOT NULL UNIQUE,
+    description     TEXT NOT NULL DEFAULT '',
+    built_in        INTEGER NOT NULL DEFAULT 0,
+    created_at      TEXT NOT NULL DEFAULT (datetime('now')),
+    updated_at      TEXT NOT NULL DEFAULT (datetime('now'))
+);
+
+-- The devices a template stamps into a project. suggested_name is
+-- pre-filled into the apply-template form; m can override.
+CREATE TABLE setup_template_devices (
+    id              INTEGER PRIMARY KEY,
+    template_id     INTEGER NOT NULL REFERENCES setup_templates(id) ON DELETE CASCADE,
+    device_type_id  INTEGER NOT NULL REFERENCES device_types(id)    ON DELETE RESTRICT,
+    suggested_name  TEXT,                        -- "TV", "Bedroom TV", "Mac (work)"
+    sort_order      INTEGER NOT NULL DEFAULT 0
+);
+CREATE INDEX setup_template_devices_template_idx ON setup_template_devices(template_id);
+
+-- Requirements between devices in the template, addressed by
+-- `setup_template_devices.id` (not the runtime device id — they're
+-- resolved at apply time).
+CREATE TABLE setup_template_requirements (
+    id                       INTEGER PRIMARY KEY,
+    template_id              INTEGER NOT NULL REFERENCES setup_templates(id) ON DELETE CASCADE,
+    from_template_device_id  INTEGER NOT NULL REFERENCES setup_template_devices(id) ON DELETE CASCADE,
+    to_template_device_id    INTEGER NOT NULL REFERENCES setup_template_devices(id) ON DELETE CASCADE,
+    preferred_cable_type_id  INTEGER REFERENCES cable_types(id) ON DELETE SET NULL,
+    must_connect             INTEGER NOT NULL DEFAULT 1 CHECK (must_connect IN (0, 1)),
+    CHECK (from_template_device_id != to_template_device_id)
+);
+CREATE INDEX setup_template_reqs_template_idx ON setup_template_requirements(template_id);
+```
+
+API:
+
+```
+GET  /api/setup-templates                          → [SetupTemplate {id, name, description, built_in,
+                                                                     devices: [{id, device_type_id,
+                                                                                device_type: {…},
+                                                                                suggested_name, sort_order}],
+                                                                     requirements: [{id, from_template_device_id,
+                                                                                     to_template_device_id,
+                                                                                     preferred_cable_type_id,
+                                                                                     must_connect}]}, …]
+                                                     Read-only; built-ins are not editable via API in v4.1.
+
+POST /api/projects/:pid/apply-template             ← {
+                                                       template_id: <int>,
+                                                       name_overrides: { <template_device_id>: "<name>", … },
+                                                       skip_devices: [<template_device_id>, …]    # optional
+                                                     }
+                                                     → {
+                                                       devices_added: [Device, …],
+                                                       requirements_added: [ConnectionRequirement, …],
+                                                       skipped_devices: [{template_device_id, reason}, …]
+                                                     }
+                                                     Idempotency:
+                                                     - A name collision with an existing device in the
+                                                       project skips that template device (reason = "name
+                                                       already in use"). Caller can pass `name_overrides`
+                                                       to resolve.
+                                                     - Requirements whose endpoints both resolve fire;
+                                                       any whose endpoint was skipped are themselves
+                                                       skipped (logged in `requirements_skipped[]` — same
+                                                       shape).
+                                                     The whole call runs in a single transaction.
+```
+
+The seed migration creates the 3 built-ins + their template_devices and
+template_requirements rows referencing the 14 built-in `device_types` and
+the 5 built-in `cable_types`. No project_id anywhere — templates are
+global.
+
 **FK shape — why `project_id` on every project-scoped row, not just transitively:**
 
 The structural truth is `cable → port → device → frame → project`. But
@@ -328,8 +643,11 @@ PATCH  /api/projects/:pid/frames/:id
 DELETE /api/projects/:pid/frames/:id
 
 GET    /api/projects/:pid/devices
-POST   /api/projects/:pid/devices                   ← {name, frame_id?, x, y, width, height, color?}
-PATCH  /api/projects/:pid/devices/:id               (e.g. {x, y} on drag)
+POST   /api/projects/:pid/devices                   ← {name, type_id?, frame_id?, x, y, width, height, color?}
+                                                     v4: type_id (optional) seeds ports from the catalog;
+                                                     without it, a freeform device (no ports) is created.
+PATCH  /api/projects/:pid/devices/:id               (e.g. {x, y} on drag). type_id can be set or cleared;
+                                                     clearing does NOT delete existing ports (instance-owned).
 DELETE /api/projects/:pid/devices/:id
 
 GET    /api/projects/:pid/devices/:id/ports
@@ -354,12 +672,90 @@ GET    /api/projects/:pid/bundles/suggestions       → [{name, cable_ids}, …]
 PATCH  /api/projects/:pid/bundles/:id
 DELETE /api/projects/:pid/bundles/:id
 
+# v4 — Device-type catalog (mostly global, project-scoped writes for custom rows)
+GET    /api/device-types                            → built-in catalog (project_id NULL) — read-only listing
+GET    /api/projects/:pid/device-types              → built-ins + this project's custom types, merged
+POST   /api/projects/:pid/device-types              ← {name, kind?, icon?, description?, ports: [{cable_type_id, count, label_prefix?, edge?}]}
+                                                     Creates a project-custom row (built_in=0); inserts
+                                                     device_type_ports rows in the same transaction.
+PATCH  /api/projects/:pid/device-types/:id          ← partial. Only project-custom types are PATCHable;
+                                                     mutating a built-in row → 403 (UI hides edit affordance).
+                                                     Editing ports replaces the device_type_ports rows;
+                                                     existing devices' ports are NOT retroactively reseeded.
+DELETE /api/projects/:pid/device-types/:id          Only project-custom; built-ins → 403.
+                                                     ON DELETE SET NULL on devices.type_id so devices
+                                                     keep their already-seeded ports.
+
+# v4 — Connection requirements (the solver's input)
+GET    /api/projects/:pid/connection-requirements   → [ConnectionRequirement, …]
+POST   /api/projects/:pid/connection-requirements   ← {from_device_id, to_device_id,
+                                                       preferred_cable_type_id?, must_connect?, notes?}
+                                                     Server normalises (from, to) into (pair_lo, pair_hi)
+                                                     before insert; duplicate (project, pair_lo, pair_hi,
+                                                     preferred_cable_type_id) → 409 conflict.
+PATCH  /api/projects/:pid/connection-requirements/:id
+DELETE /api/projects/:pid/connection-requirements/:id
+
+# v4 — Solver
+POST   /api/projects/:pid/solve                     ← {} (or {?preview=1} to compute without applying)
+                                                     → {
+                                                       cables_added:    [Cable, …],
+                                                       cables_kept:     [int, …],   # ids preserved by the diff
+                                                       cables_removed:  [int, …],   # ids deleted (auto cables only)
+                                                       bundles_added:   [{Bundle, cable_ids: [int]}, …],
+                                                       bundles_removed: [int, …],
+                                                       unsatisfied:     [{requirement_id, reason}, …],
+                                                       warnings:        [string, …],
+                                                     }
+                                                     Default applies in a single transaction. ?preview=1
+                                                     returns the same shape without writing. User-created
+                                                     cables (auto=0 in the cables table; see §5.1) are
+                                                     never touched — the solver only adds/removes its own.
+
+# v4 — Solver quick-fix combo endpoint (powers the inspector's
+# "+ Add <type> port to <device> and re-solve" button — §5b.4).
+POST   /api/projects/:pid/devices/:id/ports-and-resolve
+                                                     ← {type_id: <int>,
+                                                       label?: <str>,
+                                                       x_offset?: <num>, y_offset?: <num>}
+                                                     → {port: Port, solve: <solve response>}
+                                                     Single tx: inserts the port + re-runs solve. Used by
+                                                     the quick-fix UI so the unmet badge resolves in one
+                                                     server round-trip.
+
+# v4.1 — Setup templates
+GET    /api/setup-templates                         → [SetupTemplate, …]
+                                                     Read-only listing of built-in (and any project-custom,
+                                                     post-v4.1) templates with their device/requirement
+                                                     shapes (see §2.4).
+POST   /api/projects/:pid/apply-template            ← {template_id: <int>,
+                                                       name_overrides?: { <template_device_id>: "<name>" },
+                                                       skip_devices?: [<template_device_id>, …]}
+                                                     → {devices_added: [Device, …],
+                                                       requirements_added: [ConnectionRequirement, …],
+                                                       skipped_devices: [{template_device_id, reason}, …],
+                                                       requirements_skipped: [{template_requirement_id, reason}, …]}
+                                                     Idempotent in spirit: name collisions surface in
+                                                     skipped_devices; m resolves with name_overrides on
+                                                     re-apply. Whole call is one transaction.
+
 # Sync — export only in MVP
 POST   /api/projects/:pid/sync/export               → writes the project's drawing to mExDraw
                                                      (overwrites previous version; mExDraw keeps
                                                      git-version-history sidecar)
 ```
 
+### 3.1 v4 wire-shape additions
+
+- `ConnectionRequirement` (response):
+  `{id, project_id, from_device_id, to_device_id, preferred_cable_type_id|null, must_connect: bool, notes, created_at, updated_at}`.
+- `DeviceType` (response):
+  `{id, project_id|null, name, kind, icon|null, description, built_in: bool, ports: [{cable_type_id, count, label_prefix, edge, sort_order}]}`.
+- `cables` gets an `auto: bool` field on the row (slice 5.5 migration adds
+  the column with default 0; the solver sets 1 on its own creations). The
+  v3 cable rows m hand-drew keep `auto=0`. `POST /api/.../cables`
+  continues to default `auto=0`; only the solver writes `auto=1`.
+
 No `POST /api/sync/import` in MVP. Import is post-MVP and only ever serves
 a one-shot migration use case (e.g. seeding LOFT from the legacy
 Cable-Management drawing if m later changes his mind).
@@ -447,6 +843,139 @@ they're ignored in v0 (open question §9).
 
 ---
 
+## 5b. v4 — Solver
+
+The solver is the headline addition in v4. m's product-vision sentence
+maps onto it directly:
+
+> "I say what devices we have, the app tells me how to bundle cables and
+> how the most efficient connection looks like"
+
+The solver reads a project's `devices` (with their `ports`) and
+`connection_requirements`, and writes a set of solver-owned `cables`
+(rows with `auto=1`) + `bundles`. m's hand-drawn cables (`auto=0`) are
+left strictly alone — the solver only adds and removes its own.
+
+### 5b.1 Objective: maximum bundling — schematic only
+
+mCables is a **schematic**, not a physical-routing tool. Cables are
+straight lines between endpoints; the solver has no model of walls,
+floors, cable trays, or path geometry. "Maximum bundling" therefore
+reduces to a single rule on the schematic:
+
+> When two or more cables share the same endpoint pair (device A ↔
+> device B), group them into one bundle.
+
+This is the v3 endpoint-pair rule, applied to the solver's output. m's
+"visually cleaner setups" benefit comes from the bundle being a single
+labelled set in the inspector + a single mixed-colour glyph in the
+render (slice 9+), rather than from any path optimisation. Anything
+about trunks, frame-edge corridors, or auto-routing is out of scope —
+filed for "post-v0 ambient" in §8.
+
+### 5b.2 Algorithm (v0)
+
+Pure function. No graph search; no LP; no path optimisation. Single
+pass with greedy port allocation.
+
+```
+solve(project) ⇒ {add, remove, bundles, unsatisfied}:
+  let auto_cables_before = SELECT * FROM cables WHERE project=p AND auto=1
+  let port_free := {port_id -> bool}  initialised TRUE for every port
+                  minus ports already used by manual cables (auto=0)
+
+  for each requirement r in order(must_connect DESC, id ASC):
+    let ct = r.preferred_cable_type_id
+          ?? auto_pick_cable_type(r.from_device, r.to_device)
+          ?? fail("ambiguous")
+    let pa = first_free_port(r.from_device, ct, port_free)
+    let pb = first_free_port(r.to_device,   ct, port_free)
+    if !pa or !pb:
+      if r.must_connect: unsatisfied.push({r.id, reason})
+      else:              skip
+      continue
+    port_free[pa] = port_free[pb] = false
+    add.push(cable{type=ct, from_port=pa, to_port=pb, auto=1})
+
+  // Bundle by endpoint-pair (v3 rule, applied only to auto cables).
+  for each (device_a, device_b) pair with ≥ 2 add-cables:
+    bundles_add.push({auto=1, cables: those add-cables})
+
+  // Diff against auto_cables_before to compute remove[] (any prior auto
+  // cable whose (from, to, type) doesn't appear in add[]).
+  remove = auto_cables_before - add
+  return {add, remove, bundles_add, unsatisfied}
+```
+
+`first_free_port(device, cable_type, free_map)` picks the lowest-id port
+on the device whose `type_id` matches and that is still free, returning
+NULL if none. The `lowest-id` tiebreak is deterministic so repeated
+solves produce the same plan.
+
+`auto_pick_cable_type(from, to)` (used when `preferred_cable_type_id` is
+NULL): find the set of cable types `T = ports(from).types ∩
+ports(to).types`. If `|T| == 1`, return it. If `|T| > 1`, fail
+("ambiguous; specify preferred_cable_type_id"). The UI surfaces this
+as a "specify type" inline edit on the requirement.
+
+### 5b.3 Solver-owned vs. user-owned cables
+
+`cables.auto` distinguishes them.
+
+| Operation | Effect on `auto=0` cables | Effect on `auto=1` cables |
+|---|---|---|
+| POST /api/.../cables (m draws by hand) | inserts auto=0 | n/a |
+| PATCH cables (m moves endpoint, relabels) | applies | applies (and the cable is "promoted" to auto=0 — m owns it now) |
+| DELETE cables | applies | applies |
+| POST /api/.../solve | left alone (their used ports are reserved before the solver runs) | replaced wholesale (remove[] + add[] in one tx) |
+
+This way a manual cable m doesn't want the solver to second-guess
+survives every solve. If m wants the solver to take it over, he deletes
+his hand-drawn cable and re-solves; the solver re-creates an equivalent
+auto cable.
+
+### 5b.4 When solver fails — quick-fix UX
+
+Three classes of failure surface in the response's `unsatisfied[]`:
+
+1. **No compatible cable type** — `T = ports(from).types ∩
+   ports(to).types` is empty (e.g. a Power-only device to an HDMI-only
+   device).
+2. **Ambiguous cable type** — `|T| > 1`, no preferred set on the
+   requirement.
+3. **No free port** — the cable type matches but every port on one side
+   is already used.
+
+The solver does **not** auto-add ports without m's consent. v4.1 ships
+an explicit one-click quick-fix per class of failure, surfaced as a red
+badge on the affected device in the inspector (§7) and as a button on
+each `unsatisfied[]` entry in the preview-diff modal:
+
+| Failure class | Quick-fix button | What it does |
+|---|---|---|
+| No compatible cable type | **"+ Add &lt;preferred_type&gt; port to &lt;device&gt; and re-solve"** | POST `/api/projects/:pid/devices/:id/ports` with `type_id=preferred_type` + sensible default offset, then immediately POST `/solve` again. The preferred_type is the requirement's `preferred_cable_type_id`. If the requirement has no preferred type, the button reads "Specify cable type" and opens an inline cable-type picker on the requirement instead. |
+| Ambiguous cable type | **"Specify cable type"** | Opens an inline picker on the requirement row with the candidates from `T` pre-listed. On select → PATCH the requirement → re-solve. |
+| No free port | **"+ Add &lt;type&gt; port to &lt;device&gt; and re-solve"** | Same as the no-compat case but the `type` is already determined (it's the requirement's preferred or auto-picked type). Adds a port on whichever side ran out (the response's `reason` carries `which_side`). |
+
+All three quick-fixes do their work in a single round-trip request from
+the UI perspective: the click fires a POST that either chains the port
+insert + the re-solve server-side, or fires both calls back-to-back from
+the client (server-side chaining is simpler — see §3.2 for the endpoint
+shape).
+
+The quick-fix never adds a port silently; the button text always names
+the device + cable type so m sees what's about to mutate.
+
+### 5b.5 Preview vs. apply
+
+`?preview=1` returns the same shape without writing. The UI shows a diff
+modal with `add[]`, `remove[]`, `unsatisfied[]`; m clicks Apply to fire
+the same endpoint without `preview=1`. Default (no flag) applies
+immediately. Live-solve (no Solve button — every requirement edit
+triggers a debounced re-solve) is parked at slice 9+ as an opt-in.
+
+---
+
 ## 6. Sync — export-only for v0
 
 ```
@@ -522,16 +1051,54 @@ the new project (which has 5 seeded cable types and no frames yet).
 The currently active project's id is kept in URL state
 (`/?project=LOFT`) so reload returns to the same project.
 
+### v4.1 — Flow: apply a setup template
+
+The New Project modal gains a **"or start from a template"** section
+under the description field. Each built-in template ('Living Room',
+'Home Office', 'Server Rack') is a clickable card listing its devices +
+the requirement edges between them. Selecting one expands an inline
+override form:
+
+- A pre-filled name for each template device (m can edit each, e.g.
+  rename `TV` to `Bedroom TV`).
+- Per-device "skip" checkbox.
+
+On Create, the server does `POST /api/projects` first; on success,
+immediately fires `POST /api/projects/:pid/apply-template` with the
+collected overrides. The response's `devices_added` + `requirements_added`
+are merged into the local snapshot and the project switches to it,
+already populated.
+
+For an already-existing empty project, the inspector's project header
+shows an **"Apply template"** action that opens the same override form
+without the project-create round-trip.
+
+Once the template has stamped its devices + requirements, hit **Solve**
+(§7 "Flow: run the solver") to produce the wired diagram.
+
 ### Flow: add a frame
 
 1. `+ Frm` in the left toolbar (or `F`).
 2. Click + drag on the canvas → rubber-band rectangle becomes a frame.
 3. Name prompt centered in the frame; Enter → `POST .../frames`.
 
-### Flow: add a device
+### Flow: add a device (v4 — type-aware)
 
-Unchanged from v1: `+ Dev` (or `D`) → click on canvas → rectangle placed
-(falls into whichever frame it lands in) → name → `POST .../devices`.
+1. `+ Dev` (or `D`) → click on canvas → device placeholder appears.
+2. **First field in the inline namer: type dropdown** (replaces the
+   v1 plain-name input). Options pulled from
+   `GET /api/projects/:pid/device-types` — built-ins listed first
+   grouped by `kind`, then project-custom rows, then `Custom (no type)`.
+   Typing in the dropdown filters by `name` (m types "n" → NAS jumps
+   to top). Below the dropdown: a name input pre-filled with the type
+   name + a digit if a same-named device already exists ("PC", "PC-2").
+3. Hit Enter → `POST .../devices` with `type_id` + name. The server
+   seeds the ports from `device_type_ports` in the same transaction
+   and returns the device with its `ports`.
+4. Picking `Custom (no type)` keeps the v3 behaviour: rectangle, no
+   ports, m adds ports manually via the inspector.
+5. The device renders with its ports already visible along the
+   configured edge.
 
 ### Flow: add a port
 
@@ -581,54 +1148,140 @@ In the inspector with nothing else selected, "Bundle suggestions" pulls
 on the diagram + an Accept button. Manual: shift-click multiple cables →
 "Group as bundle" → name it → save.
 
+### v4 — Flow: declare connection requirements
+
+The left sidebar gains a **Requirements** section under the legend:
+
+```
+Cable types
+  Power, USB, HDMI, DP, RJ45, + Type
+
+Requirements                       ← new in v4
+  NAS ↔ Switch       RJ45    must
+  PC  ↔ TV           HDMI    must
+  Mac ↔ Soundbar     HDMI    nice
+  + Requirement
+```
+
+Click `+ Requirement` → modal with two device pickers (autocomplete from
+the project's current devices), a cable-type picker (defaults to
+auto-resolve if the device pair has only one matching type), and a
+must/nice toggle. `POST .../connection-requirements`.
+
+Alternative gesture (no tool armed, no selection): **drag from device A
+to device B** to seed a requirement modal with the pair pre-filled. The
+solver-edge preview drags out from the source device's edge in a thin
+dashed line until release.
+
+m can also right-click a requirement row → edit / delete.
+
+### v4 — Flow: run the solver
+
+Header gains a **Solve** button next to **Export**.
+
+1. Click Solve (or `S`) → `POST /api/projects/:pid/solve?preview=1`.
+2. A diff modal opens listing `add[]`, `remove[]`, `unsatisfied[]` — the
+   canvas behind it dims and previews the new cables in a translucent
+   stroke + the to-be-removed cables in a strikethrough red.
+3. Buttons:
+   - **Apply** → fires `POST .../solve` (no `preview`), applies in one
+     transaction, closes the modal, re-renders canvas with the real
+     cables in place.
+   - **Cancel** → leaves everything as it was.
+4. Unsatisfied requirements get their own list at the bottom of the
+   modal, each with a quick-action button: "Specify type", "+ Add port
+   to device X", or "Drop requirement (set must=0)".
+
+If `unsatisfied[]` is non-empty, the Solve button stays in a
+soft-error state (yellow) until either every requirement is satisfiable
+or m explicitly accepts the partial plan.
+
+### v4 — Inspector states
+
+| Selection | Inspector shows |
+|---|---|
+| nothing | empty, with "Bundle suggestions" + "Project requirements" headlines |
+| project header | name, drawing_name, description (editable), device count, requirement count, Solve / Export buttons |
+| frame | name (editable), x/y/w/h, contained-device count, delete |
+| **device** | name + type + icon, ports grid (type / label / connected? / +Port), **unmet requirements list** with red badges. Each badge carries a single quick-fix button — "+ Add &lt;type&gt; port to &lt;device&gt; and re-solve" (no-compat-type / no-free-port cases) or "Specify cable type" (ambiguous case) per §5b.4. delete |
+| **port** | type, label, parent device, current cable (if any), delete |
+| **cable (auto=1)** | source/target, type, driving requirement (clickable → opens requirement edit), parent bundle (if any), label, "Promote to manual" (sets auto=0) |
+| cable (auto=0) | as v3 — type, source/target, label, delete |
+| bundle | name, member cables (clickable to focus), the endpoint pair (`Device A ↔ Device B`), auto-detected flag |
+
 ### Keyboard
 
-`P` switch project (opens picker), `F` add frame, `D` add device,
-`I` add IO marker, `T` start cable from selected port,
-`E` export current project, `Esc` cancel, `Backspace` delete selection,
-`?` show shortcuts.
+`P` switch project, `F` add frame, `D` add device, `I` add IO marker,
+`T` start cable from selected port, `R` add requirement,
+**`S` solve project (v4)**, `E` export, `Esc` cancel, `Backspace` delete
+selection, `?` show shortcuts.
 
 ---
 
-## 8. First slices
+## 8. First slices — v4 reshape
 
-Each slice ends with something m can click. The first coder shift takes
-slices 1–4 as the MVP; slice 5 (export) is the round-trip end.
+Slices 1 + 2 have shipped (see git history). v4 inserts new slices ahead
+of the original 3-5 because the solver depends on the catalog + the
+requirements model, not on manual cable drawing. The old "manual port +
+cable draw" slice is still in scope as a tweak path on the solver
+output, but it follows the solver instead of leading.
 
-| # | Slice | What's shipped |
-|---|---|---|
-| 1 | **Bootstrap + project CRUD** | `cmd/mcables` Go binary, SQLite migrations. Migration 001 seeds the 5 default cable types (Power/USB/HDMI/DP/RJ45) **globally, once**. `internal/db` store. `POST /api/projects` auto-fills `drawing_name = <name>.excalidraw` when omitted. `DELETE /api/projects/:pid?confirm=<name>` with name-match guardrail. `GET /api/projects` lists them. `GET /api/projects/:pid` returns a (mostly empty) snapshot. `GET /api/cable-types` returns the 5 seeded rows. Frontend `index.html` + `main.js` shows the project picker, a "+ New Project" modal, and an empty SVG canvas with the legend rendered from the global `cable_types` table. m can create LOFT, see it picked, see no devices. |
-| 2 | **Add frame, add device, drag-to-position** | `+ Frm` and `+ Dev` tools work. Devices and frames persist. Drag-to-position writes back to DB on `pointerup`. Reload returns to the same layout. m builds LOFT's `desk` and `rack` frames and drops in his first devices. |
-| 3 | **Add port, draw cable** | `+ Port` (with a device selected) places type-coloured ports on device edges with offsets. Click-port → click-port creates a cable. Cables auto-route as straight lines. Inspector shows the cable's type, endpoints, label. m wires up the first end-to-end cable. |
-| 4 | **IO markers + cable-type editing** | `+ IO` places a wall-outlet diamond. Cable-from-port → IO commits as `to_io_id`. Legend swatch is a colour picker; renaming a type updates the legend on the fly. `+ Type` adds new types. m can fully recreate LOFT's visual model from scratch. |
-| 5 | **Export to mxdrw.msbls.de** | `POST .../sync/export` generates a `.excalidraw` scene that reproduces the seed's visual grammar (ports as positional ellipses, IO as diamonds, legend as text in the top-left), writes it via mExDraw API, and stores the assigned `excalidraw_id`s for stability on re-export. m sees LOFT in Excalidraw and confirms the look matches the seed. |
+| # | Slice | Status | What's shipped |
+|---|---|---|---|
+| 1 | **Bootstrap + project CRUD + global cable_types** | ✅ shipped | See git: branch `mai/picasso/slice-1-bootstrap`. |
+| 2 | **Frames + devices + drag** | ✅ shipped | See git: branch `mai/picasso/slice-2-frames-devices`. |
+| **3 (was 4)** | **IO markers + cable-type editing** | pending | Unchanged scope. `+ IO` places a wall-outlet diamond. Legend swatch is a colour picker; renaming a type updates the legend on the fly. `+ Type` adds new global types. |
+| **4 (NEW)** | **Device-type catalog + type-aware device create** | pending | Migration 002: `device_types` + `device_type_ports`, seeded with the 11 built-ins (§2.2). Migration adds `devices.type_id`. API: `GET /api/device-types`, `GET /api/projects/:pid/device-types`. Frontend: the +Dev inline namer becomes a type dropdown + name input; choosing a built-in type seeds the device's ports on the backend. Picking `Custom (no type)` falls back to v3 freeform. m can create a typed NAS + see its Power + RJ45 ports appear on the canvas. |
+| **4.5 (NEW)** | **Manage device-type catalog (per project)** | pending | Modal: `POST/PATCH/DELETE /api/projects/:pid/device-types` for project-custom rows. Edit affordance hidden for built-ins. Lets m add an exotic device type without contributing to the built-in catalog. Validation: a custom type can't share a name with a built-in (already enforced by `UNIQUE(project_id, name)` + a separate code-level check against built-ins). |
+| **5 (NEW)** | **Connection requirements UI + CRUD** | pending | Migration 003: `connection_requirements`. API: full CRUD under `/api/projects/:pid/connection-requirements`. Frontend: left-sidebar "Requirements" section, `+ Requirement` modal (autocomplete from project's current devices, cable-type picker, must/nice toggle). Drag from device A to device B gestures the same modal pre-filled. Inspector for a selected device lists its requirements. |
+| **6 (v4.1 EXPANDED)** | **Solver MVP + Solve button + setup templates** | pending | `POST /api/projects/:pid/solve` with `?preview=1` support. v0 algorithm (§5b.2): pure-function, greedy port allocation, endpoint-pair bundling. Migration 003 adds `cables.auto`. Header gains a Solve button that opens the preview-diff modal. m clicks Solve → sees the cable plan + unmet requirements (each with its quick-fix button per §5b.4) → applies. **Folded in v4.1: setup templates.** Migration 004 adds `setup_templates` + `setup_template_devices` + `setup_template_requirements` and seeds 3 built-ins ('Living Room', 'Home Office', 'Server Rack'). API: `GET /api/setup-templates`, `POST /api/projects/:pid/apply-template`. UI: a "Templates" section in the New Project modal + an "Apply template" action on empty projects → seeds devices + requirements in one transaction → Solve produces the wired diagram. |
+| **7 (was 3, slimmed)** | **Manual port + manual cable draw** | pending | The v3 flow as a tweak path on solver output. `+ Port` on an instance-owned device; click-port → click-port creates a hand-drawn cable (`auto=0`). Used to override the solver's choices or to extend its plan. |
+| **8 (was 5)** | **Export to mxdrw.msbls.de** | pending | `POST .../sync/export` writes a `.excalidraw` scene per the visual grammar (§4). Bundles ignored on export in v0. |
 
-Slices 6+ (not promised for the first coder shift):
-bundle suggestions UI; bundle rendering (thick path with mixed-colour
-fan-out); cable type "warn on cross-type port-to-port"; cable inventory
-metadata (length/SKU) if m later wants it; dark mode.
+Slices 9+ (not promised for the first coder shift):
+- Live-solve mode: re-run solver on every device/requirement edit with a debounce + previewed-but-not-applied diff in a toast. Opt-in toggle in project settings.
+- Bundle rendering in the SVG (a single thick line with mixed-colour stops between the endpoint pair, plus a small badge with the cable count). Cables in a bundle still render as their individual lines underneath; the bundle is a visual overlay m can toggle.
+- "Re-seed from type" action on a device.
+- Custom setup templates (m authors them in-UI, not just the built-in three).
+- Cable inventory metadata (length/SKU) if m later wants it.
+- Dark mode.
+
+Out of scope, period (would change mCables's mental model): path
+routing, cable-tray polylines, frame-edge corridors, wall-axis bundling,
+3D, anything that treats a cable as more than a labelled endpoint pair.
 
 ---
 
-## 9. Open questions for m — all resolved in v3
+## 9. Open questions for m — all closed in v4.1
 
-All six v2 questions are now answered. Locked answers:
+The six v4 questions are now answered. Locked answers:
 
-1. **Drawing-name policy** → server-side default `<name>.excalidraw` on
-   POST when omitted; editable via PATCH. (§3)
-2. **Device-name uniqueness within a project** → `UNIQUE (project_id,
-   devices.name)` enforced at the schema level. (§2)
-3. **Non-Power IO markers** → no `type_id` on `io_markers` for v0.
-   Power-by-convention; UI soft-warns on non-Power cables to an IO. (§2, §7)
-4. **Bundle render in export v1** → bundles ignored on export until slice
-   6+. (§4, §5)
-5. **Cross-project cable types** → `cable_types` is fully **global**. One
-   shared legend; renaming/recolouring affects every project. (§2, §3, §7)
-6. **Project deletion guardrail** → `DELETE /api/projects/:pid?confirm=<name>`
-   required; server validates name match, returns 400 otherwise. (§3)
+1. **Where do paths come from?** → **Nowhere — mCables is a schematic.**
+   Cables are straight lines between endpoints. The solver does not
+   route, the renderer does not route, and "maximum bundling" reduces to
+   the endpoint-pair rule (§5b.1). Anything resembling a path, trunk,
+   cable tray, or frame-edge corridor is **out of scope, period**
+   (§8 "Out of scope, period").
+2. **Live solve or button-only?** → **Button-only for v0.** Live-solve
+   stays parked at slice 9+ as an opt-in.
+3. **No-compatible-port-pair UX.** → **Explicit quick-fix.** The
+   unsatisfied-requirement badge in the inspector carries a single
+   button — "+ Add &lt;type&gt; port to &lt;device&gt; and re-solve" —
+   that POSTs the port AND fires `/solve` in one UI action. The button
+   text always names the device + type, so m sees what's about to
+   mutate (§5b.4 + §7).
+4. **Setup templates.** → **Folded INTO v4.1, in slice 6.** Migration 004
+   adds `setup_templates` + child tables + 3 built-ins. `GET
+   /api/setup-templates` and `POST /api/projects/:pid/apply-template`
+   ship alongside the solver (§2.4 + §3 + slice 6 in §8). Custom
+   templates (m authors his own) parked at slice 9+.
+5. **Catalog distribution.** → **SQL seed in migration 002.** No
+   external file loader.
+6. **Promote to manual.** → **Explicit button** on the cable inspector
+   (§7 row "cable (auto=1)"). PATCHes that only update labels stay auto.
 
 No open design questions remain. The coder shift is gated on m's
-go/no-go for v3 — not on any unanswered design question from picasso.
+go/no-go for v4.1 — not on any unanswered design question from picasso.
 
 ---
 
@@ -777,4 +1430,4 @@ gitignored.
 
 ---
 
-DESIGN v3 READY — coder shift gated
+DESIGN v4.1 READY FOR REVIEW

internal/db/bundles.go

@@ -0,0 +1,222 @@
+package db
+
+import (
+	"database/sql"
+	"errors"
+	"fmt"
+	"strings"
+)
+
+// BundleCreate is the create-shape: a name + the cable IDs to include.
+// Auto=true means the solver created the bundle; user-created bundles
+// stay auto=0 and survive a re-solve.
+type BundleCreate struct {
+	Name     string
+	CableIDs []int64
+	Auto     bool
+}
+
+type BundleUpdate struct {
+	Name     *string
+	CableIDs *[]int64
+}
+
+// CreateBundle inserts a bundle + its cable_bundle rows in one tx.
+func (s *Store) CreateBundle(projectID int64, b BundleCreate) (*Bundle, error) {
+	return s.createBundle(s.db, projectID, b, true)
+}
+
+func (s *Store) createBundle(ex execer, projectID int64, b BundleCreate, ownTx bool) (*Bundle, error) {
+	name := strings.TrimSpace(b.Name)
+	if name == "" {
+		return nil, fmt.Errorf("%w: name is required", ErrInvalidInput)
+	}
+	// When the caller already holds a tx (ownTx=false), do all validation
+	// against `ex` (the tx executor) — calling Store methods that hit
+	// s.db would deadlock against the connection the tx is holding under
+	// MaxOpenConns(1).
+	for _, cid := range b.CableIDs {
+		if _, err := s.getCableTx(ex, projectID, cid); err != nil {
+			if errors.Is(err, ErrNotFound) {
+				return nil, fmt.Errorf("%w: cable_id %d not in project", ErrInvalidInput, cid)
+			}
+			return nil, err
+		}
+	}
+	autoInt := 0
+	if b.Auto {
+		autoInt = 1
+	}
+
+	var tx *sql.Tx
+	var err error
+	useEx := ex
+	if ownTx {
+		tx, err = s.db.Begin()
+		if err != nil {
+			return nil, err
+		}
+		defer tx.Rollback()
+		useEx = tx
+	}
+	res, err := useEx.Exec(
+		`INSERT INTO bundles (project_id, name, auto) VALUES (?, ?, ?)`,
+		projectID, name, autoInt,
+	)
+	if err != nil {
+		return nil, mapWriteErr(err)
+	}
+	id, _ := res.LastInsertId()
+	for _, cid := range b.CableIDs {
+		if _, err := useEx.Exec(
+			`INSERT INTO bundle_cables (bundle_id, cable_id) VALUES (?, ?)`, id, cid,
+		); err != nil {
+			return nil, mapWriteErr(err)
+		}
+	}
+	if ownTx {
+		if err := tx.Commit(); err != nil {
+			return nil, err
+		}
+		return s.GetBundle(projectID, id)
+	}
+	// In tx-inheriting mode, build the response struct locally — the
+	// caller will re-fetch via GetBundle after commit if it needs more.
+	out := &Bundle{
+		ID: id, ProjectID: projectID, Name: name, Auto: b.Auto, CableIDs: append([]int64(nil), b.CableIDs...),
+	}
+	return out, nil
+}
+
+func (s *Store) GetBundle(projectID, id int64) (*Bundle, error) {
+	var b Bundle
+	var autoInt int
+	err := s.db.QueryRow(
+		`SELECT id, project_id, name, auto, created_at, updated_at
+		 FROM bundles WHERE id = ? AND project_id = ?`, id, projectID,
+	).Scan(&b.ID, &b.ProjectID, &b.Name, &autoInt, &b.CreatedAt, &b.UpdatedAt)
+	if errors.Is(err, sql.ErrNoRows) {
+		return nil, ErrNotFound
+	}
+	if err != nil {
+		return nil, err
+	}
+	b.Auto = autoInt != 0
+	ids, err := s.bundleCableIDs(id)
+	if err != nil {
+		return nil, err
+	}
+	b.CableIDs = ids
+	return &b, nil
+}
+
+func (s *Store) bundleCableIDs(bundleID int64) ([]int64, error) {
+	rows, err := s.db.Query(
+		`SELECT cable_id FROM bundle_cables WHERE bundle_id = ? ORDER BY cable_id`, bundleID,
+	)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	out := []int64{}
+	for rows.Next() {
+		var v int64
+		if err := rows.Scan(&v); err != nil {
+			return nil, err
+		}
+		out = append(out, v)
+	}
+	return out, rows.Err()
+}
+
+// ListBundles returns every bundle in a project, ordered by id.
+func (s *Store) ListBundles(projectID int64) ([]Bundle, error) {
+	rows, err := s.db.Query(
+		`SELECT id, project_id, name, auto, created_at, updated_at
+		 FROM bundles WHERE project_id = ? ORDER BY id`, projectID,
+	)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	out := []Bundle{}
+	for rows.Next() {
+		var b Bundle
+		var autoInt int
+		if err := rows.Scan(&b.ID, &b.ProjectID, &b.Name, &autoInt,
+			&b.CreatedAt, &b.UpdatedAt); err != nil {
+			return nil, err
+		}
+		b.Auto = autoInt != 0
+		out = append(out, b)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	for i := range out {
+		ids, err := s.bundleCableIDs(out[i].ID)
+		if err != nil {
+			return nil, err
+		}
+		out[i].CableIDs = ids
+	}
+	return out, nil
+}
+
+// UpdateBundle: name + cable set are mutable. Replacing cables wipes
+// bundle_cables and re-inserts in one tx.
+func (s *Store) UpdateBundle(projectID, id int64, u BundleUpdate) (*Bundle, error) {
+	cur, err := s.GetBundle(projectID, id)
+	if err != nil {
+		return nil, err
+	}
+	if u.Name != nil {
+		v := strings.TrimSpace(*u.Name)
+		if v == "" {
+			return nil, fmt.Errorf("%w: name cannot be empty", ErrInvalidInput)
+		}
+		cur.Name = v
+	}
+	tx, err := s.db.Begin()
+	if err != nil {
+		return nil, err
+	}
+	defer tx.Rollback()
+	if _, err := tx.Exec(
+		`UPDATE bundles SET name = ?, updated_at = datetime('now') WHERE id = ?`,
+		cur.Name, id,
+	); err != nil {
+		return nil, mapWriteErr(err)
+	}
+	if u.CableIDs != nil {
+		if _, err := tx.Exec(`DELETE FROM bundle_cables WHERE bundle_id = ?`, id); err != nil {
+			return nil, err
+		}
+		for _, cid := range *u.CableIDs {
+			if _, err := s.getCableTx(tx, projectID, cid); err != nil {
+				return nil, fmt.Errorf("%w: cable_id %d not in project", ErrInvalidInput, cid)
+			}
+			if _, err := tx.Exec(
+				`INSERT INTO bundle_cables (bundle_id, cable_id) VALUES (?, ?)`, id, cid,
+			); err != nil {
+				return nil, mapWriteErr(err)
+			}
+		}
+	}
+	if err := tx.Commit(); err != nil {
+		return nil, err
+	}
+	return s.GetBundle(projectID, id)
+}
+
+func (s *Store) DeleteBundle(projectID, id int64) error {
+	if _, err := s.GetBundle(projectID, id); err != nil {
+		return err
+	}
+	if _, err := s.db.Exec(
+		`DELETE FROM bundles WHERE id = ? AND project_id = ?`, id, projectID,
+	); err != nil {
+		return err
+	}
+	return nil
+}

internal/db/cables.go

@@ -0,0 +1,371 @@
+package db
+
+import (
+	"database/sql"
+	"errors"
+	"fmt"
+	"strings"
+)
+
+// CableEndpoint identifies one side of a cable. Exactly one of PortID /
+// DeviceID / IOID must be non-nil; the store enforces this.
+type CableEndpoint struct {
+	PortID   *int64
+	DeviceID *int64
+	IOID     *int64
+}
+
+// CableCreate is the create-shape for /api/projects/:pid/cables.
+// auto=false (default) marks the cable as m-drawn; the solver writes
+// auto=true when it places its rows.
+type CableCreate struct {
+	TypeID int64
+	Label  string
+	From   CableEndpoint
+	To     CableEndpoint
+	Auto   bool
+}
+
+// CableUpdate is a partial update. PATCHing endpoint or type on an
+// auto=1 cable should promote it to manual; handler logic does that
+// (see slice 6 §5b.3).
+type CableUpdate struct {
+	TypeID *int64
+	Label  *string
+	From   *CableEndpoint
+	To     *CableEndpoint
+	Auto   *bool
+}
+
+// CreateCable inserts a cable. Validates that the endpoints exist in
+// the same project, that exactly one of (port/device/io) is set per side,
+// and that the cable type is real.
+func (s *Store) CreateCable(projectID int64, c CableCreate) (*Cable, error) {
+	return s.createCable(s.db, projectID, c)
+}
+
+// createCable on a TX-or-DB executor; solver uses the tx form.
+func (s *Store) createCable(ex execer, projectID int64, c CableCreate) (*Cable, error) {
+	if err := s.validateEndpointEx(ex, projectID, "from", c.From); err != nil {
+		return nil, err
+	}
+	if err := s.validateEndpointEx(ex, projectID, "to", c.To); err != nil {
+		return nil, err
+	}
+	if err := s.assertCableTypeEx(ex, c.TypeID); err != nil {
+		return nil, err
+	}
+	autoInt := 0
+	if c.Auto {
+		autoInt = 1
+	}
+	res, err := ex.Exec(
+		`INSERT INTO cables
+		   (project_id, type_id, label,
+		    from_port_id, from_device_id, from_io_id,
+		    to_port_id, to_device_id, to_io_id,
+		    auto)
+		 VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?)`,
+		projectID, c.TypeID, nullableString(c.Label),
+		nullableInt64(c.From.PortID), nullableInt64(c.From.DeviceID), nullableInt64(c.From.IOID),
+		nullableInt64(c.To.PortID), nullableInt64(c.To.DeviceID), nullableInt64(c.To.IOID),
+		autoInt,
+	)
+	if err != nil {
+		return nil, mapWriteErr(err)
+	}
+	id, _ := res.LastInsertId()
+	return s.getCableTx(ex, projectID, id)
+}
+
+// validateEndpoint is the s.db variant for public CRUD callers.
+func (s *Store) validateEndpoint(projectID int64, label string, e CableEndpoint) error {
+	return s.validateEndpointEx(s.db, projectID, label, e)
+}
+
+// validateEndpointEx runs the same checks against any executor so the
+// solver can call createCable inside its tx without deadlocking on the
+// MaxOpenConns(1) connection that the tx holds.
+func (s *Store) validateEndpointEx(ex execer, projectID int64, label string, e CableEndpoint) error {
+	count := 0
+	if e.PortID != nil {
+		count++
+	}
+	if e.DeviceID != nil {
+		count++
+	}
+	if e.IOID != nil {
+		count++
+	}
+	if count != 1 {
+		return fmt.Errorf("%w: %s must specify exactly one of port/device/io", ErrInvalidInput, label)
+	}
+	if e.PortID != nil {
+		var pid int64
+		err := ex.QueryRow(`SELECT project_id FROM ports WHERE id = ?`, *e.PortID).Scan(&pid)
+		if errors.Is(err, sql.ErrNoRows) {
+			return fmt.Errorf("%w: %s port_id %d not found", ErrInvalidInput, label, *e.PortID)
+		}
+		if err != nil {
+			return err
+		}
+		if pid != projectID {
+			return fmt.Errorf("%w: %s port_id %d is in another project", ErrInvalidInput, label, *e.PortID)
+		}
+	}
+	if e.DeviceID != nil {
+		var pid int64
+		err := ex.QueryRow(`SELECT project_id FROM devices WHERE id = ?`, *e.DeviceID).Scan(&pid)
+		if errors.Is(err, sql.ErrNoRows) || (err == nil && pid != projectID) {
+			return fmt.Errorf("%w: %s device_id %d not in project", ErrInvalidInput, label, *e.DeviceID)
+		}
+		if err != nil {
+			return err
+		}
+	}
+	if e.IOID != nil {
+		var pid int64
+		err := ex.QueryRow(`SELECT project_id FROM io_markers WHERE id = ?`, *e.IOID).Scan(&pid)
+		if errors.Is(err, sql.ErrNoRows) || (err == nil && pid != projectID) {
+			return fmt.Errorf("%w: %s io_id %d not in project", ErrInvalidInput, label, *e.IOID)
+		}
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// assertCableTypeEx is a lightweight existence check against any executor.
+func (s *Store) assertCableTypeEx(ex execer, id int64) error {
+	var dummy int64
+	err := ex.QueryRow(`SELECT id FROM cable_types WHERE id = ?`, id).Scan(&dummy)
+	if errors.Is(err, sql.ErrNoRows) {
+		return fmt.Errorf("%w: cable type %d not found", ErrInvalidInput, id)
+	}
+	return err
+}
+
+func (s *Store) GetCable(projectID, id int64) (*Cable, error) {
+	return s.getCableTx(s.db, projectID, id)
+}
+
+func (s *Store) getCableTx(ex execer, projectID, id int64) (*Cable, error) {
+	var c Cable
+	var fp, fd, fio, tp, td, tio sql.NullInt64
+	var label, ex2 sql.NullString
+	var autoInt int
+	err := ex.QueryRow(
+		`SELECT id, project_id, type_id, label,
+		        from_port_id, from_device_id, from_io_id,
+		        to_port_id, to_device_id, to_io_id,
+		        auto, excalidraw_id, created_at, updated_at
+		 FROM cables WHERE id = ? AND project_id = ?`, id, projectID,
+	).Scan(&c.ID, &c.ProjectID, &c.TypeID, &label,
+		&fp, &fd, &fio, &tp, &td, &tio,
+		&autoInt, &ex2, &c.CreatedAt, &c.UpdatedAt)
+	if errors.Is(err, sql.ErrNoRows) {
+		return nil, ErrNotFound
+	}
+	if err != nil {
+		return nil, err
+	}
+	if label.Valid {
+		v := label.String
+		c.Label = &v
+	}
+	if fp.Valid {
+		v := fp.Int64
+		c.FromPortID = &v
+	}
+	if fd.Valid {
+		v := fd.Int64
+		c.FromDeviceID = &v
+	}
+	if fio.Valid {
+		v := fio.Int64
+		c.FromIOID = &v
+	}
+	if tp.Valid {
+		v := tp.Int64
+		c.ToPortID = &v
+	}
+	if td.Valid {
+		v := td.Int64
+		c.ToDeviceID = &v
+	}
+	if tio.Valid {
+		v := tio.Int64
+		c.ToIOID = &v
+	}
+	c.Auto = autoInt != 0
+	if ex2.Valid {
+		c.ExcalidrawID = &ex2.String
+	}
+	return &c, nil
+}
+
+// ListCables returns every cable in a project.
+func (s *Store) ListCables(projectID int64) ([]Cable, error) {
+	return s.listCablesTx(s.db, projectID)
+}
+
+func (s *Store) listCablesTx(ex execer, projectID int64) ([]Cable, error) {
+	rows, err := ex.Query(
+		`SELECT id, project_id, type_id, label,
+		        from_port_id, from_device_id, from_io_id,
+		        to_port_id, to_device_id, to_io_id,
+		        auto, excalidraw_id, created_at, updated_at
+		 FROM cables WHERE project_id = ? ORDER BY id`, projectID,
+	)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	out := []Cable{}
+	for rows.Next() {
+		var c Cable
+		var fp, fd, fio, tp, td, tio sql.NullInt64
+		var label, ex2 sql.NullString
+		var autoInt int
+		if err := rows.Scan(&c.ID, &c.ProjectID, &c.TypeID, &label,
+			&fp, &fd, &fio, &tp, &td, &tio,
+			&autoInt, &ex2, &c.CreatedAt, &c.UpdatedAt); err != nil {
+			return nil, err
+		}
+		if label.Valid {
+			v := label.String
+			c.Label = &v
+		}
+		if fp.Valid {
+			v := fp.Int64
+			c.FromPortID = &v
+		}
+		if fd.Valid {
+			v := fd.Int64
+			c.FromDeviceID = &v
+		}
+		if fio.Valid {
+			v := fio.Int64
+			c.FromIOID = &v
+		}
+		if tp.Valid {
+			v := tp.Int64
+			c.ToPortID = &v
+		}
+		if td.Valid {
+			v := td.Int64
+			c.ToDeviceID = &v
+		}
+		if tio.Valid {
+			v := tio.Int64
+			c.ToIOID = &v
+		}
+		c.Auto = autoInt != 0
+		if ex2.Valid {
+			c.ExcalidrawID = &ex2.String
+		}
+		out = append(out, c)
+	}
+	return out, rows.Err()
+}
+
+// UpdateCable applies a partial update. Caller-controlled — promote-to-
+// manual semantics live at the handler level (§5b.3: any PATCH touching
+// type/endpoint promotes auto→0).
+func (s *Store) UpdateCable(projectID, id int64, u CableUpdate) (*Cable, error) {
+	cur, err := s.GetCable(projectID, id)
+	if err != nil {
+		return nil, err
+	}
+	if u.TypeID != nil {
+		if _, err := s.GetCableType(*u.TypeID); err != nil {
+			if errors.Is(err, ErrNotFound) {
+				return nil, fmt.Errorf("%w: cable type %d not found", ErrInvalidInput, *u.TypeID)
+			}
+			return nil, err
+		}
+		cur.TypeID = *u.TypeID
+	}
+	if u.Label != nil {
+		v := strings.TrimSpace(*u.Label)
+		if v == "" {
+			cur.Label = nil
+		} else {
+			cur.Label = &v
+		}
+	}
+	if u.From != nil {
+		if err := s.validateEndpoint(projectID, "from", *u.From); err != nil {
+			return nil, err
+		}
+		cur.FromPortID = u.From.PortID
+		cur.FromDeviceID = u.From.DeviceID
+		cur.FromIOID = u.From.IOID
+	}
+	if u.To != nil {
+		if err := s.validateEndpoint(projectID, "to", *u.To); err != nil {
+			return nil, err
+		}
+		cur.ToPortID = u.To.PortID
+		cur.ToDeviceID = u.To.DeviceID
+		cur.ToIOID = u.To.IOID
+	}
+	if u.Auto != nil {
+		cur.Auto = *u.Auto
+	}
+	autoInt := 0
+	if cur.Auto {
+		autoInt = 1
+	}
+	if _, err := s.db.Exec(
+		`UPDATE cables
+		 SET type_id = ?, label = ?,
+		     from_port_id = ?, from_device_id = ?, from_io_id = ?,
+		     to_port_id = ?, to_device_id = ?, to_io_id = ?,
+		     auto = ?, updated_at = datetime('now')
+		 WHERE id = ? AND project_id = ?`,
+		cur.TypeID, nullableStringPtr(cur.Label),
+		nullableInt64(cur.FromPortID), nullableInt64(cur.FromDeviceID), nullableInt64(cur.FromIOID),
+		nullableInt64(cur.ToPortID), nullableInt64(cur.ToDeviceID), nullableInt64(cur.ToIOID),
+		autoInt, id, projectID,
+	); err != nil {
+		return nil, mapWriteErr(err)
+	}
+	return s.GetCable(projectID, id)
+}
+
+// DeleteCable removes a cable from a project.
+func (s *Store) DeleteCable(projectID, id int64) error {
+	if _, err := s.GetCable(projectID, id); err != nil {
+		return err
+	}
+	if _, err := s.db.Exec(
+		`DELETE FROM cables WHERE id = ? AND project_id = ?`, id, projectID,
+	); err != nil {
+		return err
+	}
+	return nil
+}
+
+// nullableString → for label-style strings: "" → SQL NULL.
+func nullableString(s string) any {
+	if s == "" {
+		return nil
+	}
+	return s
+}
+func nullableStringPtr(p *string) any {
+	if p == nil {
+		return nil
+	}
+	return *p
+}
+
+// execer abstracts *sql.DB and *sql.Tx for store helpers used by both
+// the public API and inside transactions (e.g. the solver).
+type execer interface {
+	Exec(query string, args ...any) (sql.Result, error)
+	Query(query string, args ...any) (*sql.Rows, error)
+	QueryRow(query string, args ...any) *sql.Row
+}

internal/db/connection_requirements.go

@@ -0,0 +1,192 @@
+package db
+
+import (
+	"database/sql"
+	"errors"
+	"fmt"
+)
+
+// ConnectionRequirementCreate is the create-shape. Server normalises
+// from/to into (pair_lo, pair_hi) so (A,B,T) and (B,A,T) collide.
+type ConnectionRequirementCreate struct {
+	FromDeviceID         int64
+	ToDeviceID           int64
+	PreferredCableTypeID *int64
+	MustConnect          *bool // pointer so "absent" defaults to true
+	Notes                string
+}
+
+// ConnectionRequirementUpdate is the partial-update shape. project_id +
+// the device pair are immutable post-create (changing either is best
+// modelled as delete-then-create — keeps pair_lo/pair_hi semantics simple).
+type ConnectionRequirementUpdate struct {
+	PreferredCableTypeID FrameRef // tri-state: leave / set / clear
+	MustConnect          *bool
+	Notes                *string
+}
+
+// CreateConnectionRequirement inserts a new requirement. Validates that
+// both devices live in projectID, that from != to, and that the
+// (project, pair_lo, pair_hi, preferred_cable_type_id) tuple is unique.
+func (s *Store) CreateConnectionRequirement(projectID int64, r ConnectionRequirementCreate) (*ConnectionRequirement, error) {
+	if r.FromDeviceID == r.ToDeviceID {
+		return nil, fmt.Errorf("%w: from_device_id and to_device_id must differ", ErrInvalidInput)
+	}
+	if _, err := s.GetProject(projectID); err != nil {
+		return nil, err
+	}
+	if _, err := s.GetDevice(projectID, r.FromDeviceID); err != nil {
+		if errors.Is(err, ErrNotFound) {
+			return nil, fmt.Errorf("%w: from_device_id %d not in project %d", ErrInvalidInput, r.FromDeviceID, projectID)
+		}
+		return nil, err
+	}
+	if _, err := s.GetDevice(projectID, r.ToDeviceID); err != nil {
+		if errors.Is(err, ErrNotFound) {
+			return nil, fmt.Errorf("%w: to_device_id %d not in project %d", ErrInvalidInput, r.ToDeviceID, projectID)
+		}
+		return nil, err
+	}
+	if r.PreferredCableTypeID != nil {
+		if _, err := s.GetCableType(*r.PreferredCableTypeID); err != nil {
+			if errors.Is(err, ErrNotFound) {
+				return nil, fmt.Errorf("%w: preferred_cable_type_id %d not found", ErrInvalidInput, *r.PreferredCableTypeID)
+			}
+			return nil, err
+		}
+	}
+	must := true
+	if r.MustConnect != nil {
+		must = *r.MustConnect
+	}
+	mustInt := 0
+	if must {
+		mustInt = 1
+	}
+	lo, hi := r.FromDeviceID, r.ToDeviceID
+	if lo > hi {
+		lo, hi = hi, lo
+	}
+	res, err := s.db.Exec(
+		`INSERT INTO connection_requirements
+		   (project_id, from_device_id, to_device_id, preferred_cable_type_id,
+		    must_connect, notes, pair_lo, pair_hi)
+		 VALUES (?, ?, ?, ?, ?, ?, ?, ?)`,
+		projectID, r.FromDeviceID, r.ToDeviceID, nullableInt64(r.PreferredCableTypeID),
+		mustInt, r.Notes, lo, hi,
+	)
+	if err != nil {
+		return nil, mapWriteErr(err)
+	}
+	id, _ := res.LastInsertId()
+	return s.GetConnectionRequirement(projectID, id)
+}
+
+// GetConnectionRequirement loads one by id, project-scoped.
+func (s *Store) GetConnectionRequirement(projectID, id int64) (*ConnectionRequirement, error) {
+	var r ConnectionRequirement
+	var ct sql.NullInt64
+	var must int
+	err := s.db.QueryRow(
+		`SELECT id, project_id, from_device_id, to_device_id, preferred_cable_type_id,
+		        must_connect, notes, created_at, updated_at
+		 FROM connection_requirements WHERE id = ? AND project_id = ?`, id, projectID,
+	).Scan(&r.ID, &r.ProjectID, &r.FromDeviceID, &r.ToDeviceID, &ct,
+		&must, &r.Notes, &r.CreatedAt, &r.UpdatedAt)
+	if errors.Is(err, sql.ErrNoRows) {
+		return nil, ErrNotFound
+	}
+	if err != nil {
+		return nil, err
+	}
+	if ct.Valid {
+		v := ct.Int64
+		r.PreferredCableTypeID = &v
+	}
+	r.MustConnect = must != 0
+	return &r, nil
+}
+
+// ListConnectionRequirements returns every requirement in a project,
+// ordered by id (insertion order).
+func (s *Store) ListConnectionRequirements(projectID int64) ([]ConnectionRequirement, error) {
+	rows, err := s.db.Query(
+		`SELECT id, project_id, from_device_id, to_device_id, preferred_cable_type_id,
+		        must_connect, notes, created_at, updated_at
+		 FROM connection_requirements WHERE project_id = ? ORDER BY id`, projectID,
+	)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	out := []ConnectionRequirement{}
+	for rows.Next() {
+		var r ConnectionRequirement
+		var ct sql.NullInt64
+		var must int
+		if err := rows.Scan(&r.ID, &r.ProjectID, &r.FromDeviceID, &r.ToDeviceID, &ct,
+			&must, &r.Notes, &r.CreatedAt, &r.UpdatedAt); err != nil {
+			return nil, err
+		}
+		if ct.Valid {
+			v := ct.Int64
+			r.PreferredCableTypeID = &v
+		}
+		r.MustConnect = must != 0
+		out = append(out, r)
+	}
+	return out, rows.Err()
+}
+
+// UpdateConnectionRequirement applies a partial update. preferred_cable_type_id
+// uses the FrameRef tri-state; must_connect + notes are plain pointers.
+// The (from, to) pair is immutable on PATCH — delete + recreate to change.
+func (s *Store) UpdateConnectionRequirement(projectID, id int64, u ConnectionRequirementUpdate) (*ConnectionRequirement, error) {
+	cur, err := s.GetConnectionRequirement(projectID, id)
+	if err != nil {
+		return nil, err
+	}
+	if u.PreferredCableTypeID.Set {
+		if u.PreferredCableTypeID.ID != nil {
+			if _, err := s.GetCableType(*u.PreferredCableTypeID.ID); err != nil {
+				if errors.Is(err, ErrNotFound) {
+					return nil, fmt.Errorf("%w: preferred_cable_type_id %d not found", ErrInvalidInput, *u.PreferredCableTypeID.ID)
+				}
+				return nil, err
+			}
+		}
+		cur.PreferredCableTypeID = u.PreferredCableTypeID.ID
+	}
+	if u.MustConnect != nil {
+		cur.MustConnect = *u.MustConnect
+	}
+	if u.Notes != nil {
+		cur.Notes = *u.Notes
+	}
+	mustInt := 0
+	if cur.MustConnect {
+		mustInt = 1
+	}
+	if _, err := s.db.Exec(
+		`UPDATE connection_requirements
+		 SET preferred_cable_type_id = ?, must_connect = ?, notes = ?, updated_at = datetime('now')
+		 WHERE id = ? AND project_id = ?`,
+		nullableInt64(cur.PreferredCableTypeID), mustInt, cur.Notes, id, projectID,
+	); err != nil {
+		return nil, mapWriteErr(err)
+	}
+	return s.GetConnectionRequirement(projectID, id)
+}
+
+// DeleteConnectionRequirement removes a requirement by id, project-scoped.
+func (s *Store) DeleteConnectionRequirement(projectID, id int64) error {
+	if _, err := s.GetConnectionRequirement(projectID, id); err != nil {
+		return err
+	}
+	if _, err := s.db.Exec(
+		`DELETE FROM connection_requirements WHERE id = ? AND project_id = ?`, id, projectID,
+	); err != nil {
+		return err
+	}
+	return nil
+}

internal/db/connection_requirements_test.go

@@ -0,0 +1,181 @@
+package db
+
+import (
+	"errors"
+	"testing"
+)
+
+func setupTwoDevices(t *testing.T, s *Store) (int64, int64, int64) {
+	t.Helper()
+	p, _ := s.CreateProject("LOFT", "", "")
+	a, _ := s.CreateDevice(p.ID, DeviceCreate{Name: "NAS", X: 0, Y: 0, Width: 100, Height: 35})
+	b, _ := s.CreateDevice(p.ID, DeviceCreate{Name: "Switch", X: 200, Y: 0, Width: 100, Height: 35})
+	return p.ID, a.ID, b.ID
+}
+
+func TestCreateConnReq_Basic(t *testing.T) {
+	s := newTestStore(t)
+	pid, a, b := setupTwoDevices(t, s)
+	rj45 := int64(5)
+	r, err := s.CreateConnectionRequirement(pid, ConnectionRequirementCreate{
+		FromDeviceID: a, ToDeviceID: b, PreferredCableTypeID: &rj45,
+	})
+	if err != nil {
+		t.Fatalf("create: %v", err)
+	}
+	if !r.MustConnect {
+		t.Errorf("must_connect default should be true")
+	}
+	if r.PreferredCableTypeID == nil || *r.PreferredCableTypeID != rj45 {
+		t.Errorf("preferred_cable_type_id wrong: %+v", r.PreferredCableTypeID)
+	}
+}
+
+func TestCreateConnReq_PairNormalisationRejectsReverse(t *testing.T) {
+	s := newTestStore(t)
+	pid, a, b := setupTwoDevices(t, s)
+	rj45 := int64(5)
+	if _, err := s.CreateConnectionRequirement(pid, ConnectionRequirementCreate{
+		FromDeviceID: a, ToDeviceID: b, PreferredCableTypeID: &rj45,
+	}); err != nil {
+		t.Fatalf("first: %v", err)
+	}
+	// (B, A, RJ45) should collide on UNIQUE (pair_lo, pair_hi, type).
+	_, err := s.CreateConnectionRequirement(pid, ConnectionRequirementCreate{
+		FromDeviceID: b, ToDeviceID: a, PreferredCableTypeID: &rj45,
+	})
+	if !errors.Is(err, ErrConflict) {
+		t.Errorf("reverse pair err = %v, want ErrConflict", err)
+	}
+}
+
+func TestCreateConnReq_DifferentCableTypesCoexist(t *testing.T) {
+	s := newTestStore(t)
+	pid, a, b := setupTwoDevices(t, s)
+	rj45, power := int64(5), int64(1)
+	if _, err := s.CreateConnectionRequirement(pid, ConnectionRequirementCreate{
+		FromDeviceID: a, ToDeviceID: b, PreferredCableTypeID: &rj45,
+	}); err != nil {
+		t.Fatalf("rj45: %v", err)
+	}
+	if _, err := s.CreateConnectionRequirement(pid, ConnectionRequirementCreate{
+		FromDeviceID: a, ToDeviceID: b, PreferredCableTypeID: &power,
+	}); err != nil {
+		t.Errorf("power on same pair should be allowed: %v", err)
+	}
+}
+
+func TestCreateConnReq_SelfLoopRejected(t *testing.T) {
+	s := newTestStore(t)
+	pid, a, _ := setupTwoDevices(t, s)
+	_, err := s.CreateConnectionRequirement(pid, ConnectionRequirementCreate{
+		FromDeviceID: a, ToDeviceID: a,
+	})
+	if !errors.Is(err, ErrInvalidInput) {
+		t.Errorf("self-loop err = %v, want ErrInvalidInput", err)
+	}
+}
+
+func TestCreateConnReq_CrossProjectDeviceRejected(t *testing.T) {
+	s := newTestStore(t)
+	pid, a, _ := setupTwoDevices(t, s)
+	p2, _ := s.CreateProject("OFFICE", "", "")
+	b2, _ := s.CreateDevice(p2.ID, DeviceCreate{Name: "X", X: 0, Y: 0, Width: 100, Height: 35})
+	_, err := s.CreateConnectionRequirement(pid, ConnectionRequirementCreate{
+		FromDeviceID: a, ToDeviceID: b2.ID,
+	})
+	if !errors.Is(err, ErrInvalidInput) {
+		t.Errorf("cross-project to-device err = %v, want ErrInvalidInput", err)
+	}
+}
+
+func TestCreateConnReq_NullCableTypeUniqueByPair(t *testing.T) {
+	// Two NULL-cable-type reqs on the same pair are NOT a conflict in
+	// SQLite (NULL != NULL in UNIQUE comparisons). This is fine — they
+	// represent "solver picks" both times; the second wins when solving.
+	s := newTestStore(t)
+	pid, a, b := setupTwoDevices(t, s)
+	if _, err := s.CreateConnectionRequirement(pid, ConnectionRequirementCreate{
+		FromDeviceID: a, ToDeviceID: b,
+	}); err != nil {
+		t.Fatalf("first: %v", err)
+	}
+	if _, err := s.CreateConnectionRequirement(pid, ConnectionRequirementCreate{
+		FromDeviceID: a, ToDeviceID: b,
+	}); err != nil {
+		t.Errorf("second NULL-type req should be allowed (SQLite NULL != NULL): %v", err)
+	}
+}
+
+func TestUpdateConnReq_PartialFields(t *testing.T) {
+	s := newTestStore(t)
+	pid, a, b := setupTwoDevices(t, s)
+	rj45, power := int64(5), int64(1)
+	r, _ := s.CreateConnectionRequirement(pid, ConnectionRequirementCreate{
+		FromDeviceID: a, ToDeviceID: b, PreferredCableTypeID: &rj45,
+	})
+	notes := "important"
+	must := false
+	updated, err := s.UpdateConnectionRequirement(pid, r.ID, ConnectionRequirementUpdate{
+		PreferredCableTypeID: FrameRef{Set: true, ID: &power},
+		MustConnect:          &must,
+		Notes:                &notes,
+	})
+	if err != nil {
+		t.Fatalf("update: %v", err)
+	}
+	if updated.PreferredCableTypeID == nil || *updated.PreferredCableTypeID != power {
+		t.Errorf("cable type not switched: %+v", updated.PreferredCableTypeID)
+	}
+	if updated.MustConnect {
+		t.Errorf("must_connect should be false")
+	}
+	if updated.Notes != "important" {
+		t.Errorf("notes = %q", updated.Notes)
+	}
+
+	// Clear the cable type.
+	cleared, _ := s.UpdateConnectionRequirement(pid, r.ID, ConnectionRequirementUpdate{
+		PreferredCableTypeID: FrameRef{Set: true, ID: nil},
+	})
+	if cleared.PreferredCableTypeID != nil {
+		t.Errorf("preferred_cable_type_id should be nil after clear; got %v", *cleared.PreferredCableTypeID)
+	}
+}
+
+func TestDeleteConnReq_CascadesOnDeviceDelete(t *testing.T) {
+	s := newTestStore(t)
+	pid, a, b := setupTwoDevices(t, s)
+	r, _ := s.CreateConnectionRequirement(pid, ConnectionRequirementCreate{
+		FromDeviceID: a, ToDeviceID: b,
+	})
+	if err := s.DeleteDevice(pid, a); err != nil {
+		t.Fatalf("delete device a: %v", err)
+	}
+	if _, err := s.GetConnectionRequirement(pid, r.ID); !errors.Is(err, ErrNotFound) {
+		t.Errorf("requirement should be gone after device delete; got %v", err)
+	}
+}
+
+func TestSnapshot_IncludesConnectionRequirements(t *testing.T) {
+	s := newTestStore(t)
+	pid, a, b := setupTwoDevices(t, s)
+	_, _ = s.CreateConnectionRequirement(pid, ConnectionRequirementCreate{
+		FromDeviceID: a, ToDeviceID: b,
+	})
+	snap, err := s.Snapshot(pid)
+	if err != nil {
+		t.Fatalf("snapshot: %v", err)
+	}
+	if len(snap.ConnectionRequirements) != 1 {
+		t.Errorf("snapshot.connection_requirements = %d, want 1", len(snap.ConnectionRequirements))
+	}
+}
+
+func TestDeleteConnReq_NotFound(t *testing.T) {
+	s := newTestStore(t)
+	p, _ := s.CreateProject("LOFT", "", "")
+	if err := s.DeleteConnectionRequirement(p.ID, 999); !errors.Is(err, ErrNotFound) {
+		t.Errorf("got %v, want ErrNotFound", err)
+	}
+}

internal/db/device_types.go

@@ -0,0 +1,351 @@
+package db
+
+import (
+	"database/sql"
+	"errors"
+	"fmt"
+	"strings"
+)
+
+// ErrForbidden is the sentinel for "you can't mutate this row" — used by
+// PATCH/DELETE on built-in device_types.
+var ErrForbidden = errors.New("forbidden")
+
+// -----------------------------------------------------------------------------
+// device_types
+// -----------------------------------------------------------------------------
+
+// DeviceTypeCreate is the shape POSTed under /api/projects/:pid/device-types.
+// project_id is the URL :pid; the caller never passes it in the body.
+type DeviceTypeCreate struct {
+	Name        string
+	Kind        string
+	Icon        string
+	Description string
+	Ports       []DeviceTypePortCreate
+}
+
+// DeviceTypePortCreate is one row in the type's port profile.
+type DeviceTypePortCreate struct {
+	CableTypeID int64
+	LabelPrefix string
+	Count       int
+	Edge        string
+	SortOrder   int
+}
+
+// DeviceTypeUpdate is the partial-update shape. Built-in types reject
+// any PATCH at the store level.
+type DeviceTypeUpdate struct {
+	Name        *string
+	Kind        *string
+	Icon        *string
+	Description *string
+	// Ports != nil means "replace the port profile with this set".
+	Ports *[]DeviceTypePortCreate
+}
+
+// CreateDeviceType inserts a project-custom row + its port profile in
+// one transaction. projectID must be non-zero (built-ins are seed-only).
+func (s *Store) CreateDeviceType(projectID int64, dt DeviceTypeCreate) (*DeviceType, error) {
+	name := strings.TrimSpace(dt.Name)
+	if name == "" {
+		return nil, fmt.Errorf("%w: name is required", ErrInvalidInput)
+	}
+	if projectID == 0 {
+		return nil, fmt.Errorf("%w: project_id is required (built-ins are seed-only)", ErrInvalidInput)
+	}
+	if _, err := s.GetProject(projectID); err != nil {
+		return nil, err
+	}
+	// Forbid name-collisions with built-ins (UNIQUE(project_id,name)
+	// only enforces inside the project; built-ins have project_id IS
+	// NULL so the constraint doesn't catch them).
+	var builtinClash int
+	if err := s.db.QueryRow(
+		`SELECT COUNT(*) FROM device_types WHERE project_id IS NULL AND name = ?`, name,
+	).Scan(&builtinClash); err != nil {
+		return nil, err
+	}
+	if builtinClash > 0 {
+		return nil, fmt.Errorf("%w: name %q clashes with a built-in device type", ErrConflict, name)
+	}
+
+	kind := strings.TrimSpace(dt.Kind)
+	if kind == "" {
+		kind = "generic"
+	}
+	desc := dt.Description
+	var iconPtr any
+	if icon := strings.TrimSpace(dt.Icon); icon != "" {
+		iconPtr = icon
+	}
+
+	tx, err := s.db.Begin()
+	if err != nil {
+		return nil, err
+	}
+	defer tx.Rollback()
+
+	res, err := tx.Exec(
+		`INSERT INTO device_types (project_id, name, kind, icon, description, built_in)
+		 VALUES (?, ?, ?, ?, ?, 0)`,
+		projectID, name, kind, iconPtr, desc,
+	)
+	if err != nil {
+		return nil, mapWriteErr(err)
+	}
+	id, _ := res.LastInsertId()
+
+	for _, p := range dt.Ports {
+		if err := insertDeviceTypePort(tx, id, p); err != nil {
+			return nil, err
+		}
+	}
+	if err := tx.Commit(); err != nil {
+		return nil, err
+	}
+	return s.GetDeviceType(id)
+}
+
+func insertDeviceTypePort(tx *sql.Tx, deviceTypeID int64, p DeviceTypePortCreate) error {
+	if p.CableTypeID <= 0 {
+		return fmt.Errorf("%w: cable_type_id is required on each port row", ErrInvalidInput)
+	}
+	if p.Count <= 0 {
+		p.Count = 1
+	}
+	edge := strings.TrimSpace(p.Edge)
+	if edge == "" {
+		edge = "bottom"
+	}
+	if edge != "top" && edge != "bottom" && edge != "left" && edge != "right" {
+		return fmt.Errorf("%w: edge must be top/bottom/left/right", ErrInvalidInput)
+	}
+	_, err := tx.Exec(
+		`INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+		 VALUES (?, ?, ?, ?, ?, ?)`,
+		deviceTypeID, p.CableTypeID, p.LabelPrefix, p.Count, edge, p.SortOrder,
+	)
+	if err != nil {
+		return mapWriteErr(err)
+	}
+	return nil
+}
+
+// GetDeviceType loads a single type row (built-in OR project-custom)
+// with its port profile.
+func (s *Store) GetDeviceType(id int64) (*DeviceType, error) {
+	dt, err := scanDeviceTypeByID(s.db, id)
+	if err != nil {
+		return nil, err
+	}
+	ports, err := s.listDeviceTypePorts(id)
+	if err != nil {
+		return nil, err
+	}
+	dt.Ports = ports
+	return dt, nil
+}
+
+func scanDeviceTypeByID(d *sql.DB, id int64) (*DeviceType, error) {
+	var dt DeviceType
+	var proj sql.NullInt64
+	var icon sql.NullString
+	var built int
+	err := d.QueryRow(
+		`SELECT id, project_id, name, kind, icon, description, built_in, created_at, updated_at
+		 FROM device_types WHERE id = ?`, id,
+	).Scan(&dt.ID, &proj, &dt.Name, &dt.Kind, &icon, &dt.Description, &built,
+		&dt.CreatedAt, &dt.UpdatedAt)
+	if errors.Is(err, sql.ErrNoRows) {
+		return nil, ErrNotFound
+	}
+	if err != nil {
+		return nil, err
+	}
+	if proj.Valid {
+		v := proj.Int64
+		dt.ProjectID = &v
+	}
+	if icon.Valid {
+		dt.Icon = &icon.String
+	}
+	dt.BuiltIn = built != 0
+	return &dt, nil
+}
+
+// ListBuiltInDeviceTypes returns every built-in type (project_id IS NULL).
+func (s *Store) ListBuiltInDeviceTypes() ([]DeviceType, error) {
+	return s.listDeviceTypesWhere(`project_id IS NULL`, nil)
+}
+
+// ListDeviceTypesForProject returns built-ins + the project's custom
+// types, merged. Built-ins come first (insertion order), then custom by
+// id.
+func (s *Store) ListDeviceTypesForProject(projectID int64) ([]DeviceType, error) {
+	return s.listDeviceTypesWhere(
+		`project_id IS NULL OR project_id = ?`, []any{projectID},
+	)
+}
+
+func (s *Store) listDeviceTypesWhere(where string, args []any) ([]DeviceType, error) {
+	q := `SELECT id, project_id, name, kind, icon, description, built_in, created_at, updated_at
+	      FROM device_types WHERE ` + where +
+		` ORDER BY (project_id IS NOT NULL), id`
+	rows, err := s.db.Query(q, args...)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	out := []DeviceType{}
+	for rows.Next() {
+		var dt DeviceType
+		var proj sql.NullInt64
+		var icon sql.NullString
+		var built int
+		if err := rows.Scan(&dt.ID, &proj, &dt.Name, &dt.Kind, &icon, &dt.Description, &built,
+			&dt.CreatedAt, &dt.UpdatedAt); err != nil {
+			return nil, err
+		}
+		if proj.Valid {
+			v := proj.Int64
+			dt.ProjectID = &v
+		}
+		if icon.Valid {
+			dt.Icon = &icon.String
+		}
+		dt.BuiltIn = built != 0
+		out = append(out, dt)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	// Hydrate ports per row. Two queries per request is fine for the
+	// catalog size; switch to a single JOIN-and-group if it becomes hot.
+	for i := range out {
+		ps, err := s.listDeviceTypePorts(out[i].ID)
+		if err != nil {
+			return nil, err
+		}
+		out[i].Ports = ps
+	}
+	return out, nil
+}
+
+func (s *Store) listDeviceTypePorts(deviceTypeID int64) ([]DeviceTypePort, error) {
+	rows, err := s.db.Query(
+		`SELECT id, device_type_id, cable_type_id, label_prefix, count, edge, sort_order
+		 FROM device_type_ports WHERE device_type_id = ? ORDER BY sort_order, id`,
+		deviceTypeID,
+	)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	out := []DeviceTypePort{}
+	for rows.Next() {
+		var p DeviceTypePort
+		if err := rows.Scan(&p.ID, &p.DeviceTypeID, &p.CableTypeID,
+			&p.LabelPrefix, &p.Count, &p.Edge, &p.SortOrder); err != nil {
+			return nil, err
+		}
+		out = append(out, p)
+	}
+	return out, rows.Err()
+}
+
+// UpdateDeviceType applies a partial update. Built-in rows are rejected
+// with ErrForbidden. Cross-project rows are rejected with ErrNotFound.
+// Replacing the port profile (Ports != nil) wipes and re-inserts.
+func (s *Store) UpdateDeviceType(projectID, id int64, u DeviceTypeUpdate) (*DeviceType, error) {
+	cur, err := s.GetDeviceType(id)
+	if err != nil {
+		return nil, err
+	}
+	if cur.BuiltIn {
+		return nil, fmt.Errorf("%w: built-in device types are read-only", ErrForbidden)
+	}
+	if cur.ProjectID == nil || *cur.ProjectID != projectID {
+		return nil, ErrNotFound
+	}
+
+	if u.Name != nil {
+		v := strings.TrimSpace(*u.Name)
+		if v == "" {
+			return nil, fmt.Errorf("%w: name cannot be empty", ErrInvalidInput)
+		}
+		cur.Name = v
+	}
+	if u.Kind != nil {
+		v := strings.TrimSpace(*u.Kind)
+		if v == "" {
+			v = "generic"
+		}
+		cur.Kind = v
+	}
+	if u.Icon != nil {
+		v := strings.TrimSpace(*u.Icon)
+		if v == "" {
+			cur.Icon = nil
+		} else {
+			cur.Icon = &v
+		}
+	}
+	if u.Description != nil {
+		cur.Description = *u.Description
+	}
+
+	tx, err := s.db.Begin()
+	if err != nil {
+		return nil, err
+	}
+	defer tx.Rollback()
+
+	var iconArg any
+	if cur.Icon != nil {
+		iconArg = *cur.Icon
+	}
+	if _, err := tx.Exec(
+		`UPDATE device_types
+		 SET name = ?, kind = ?, icon = ?, description = ?, updated_at = datetime('now')
+		 WHERE id = ?`,
+		cur.Name, cur.Kind, iconArg, cur.Description, id,
+	); err != nil {
+		return nil, mapWriteErr(err)
+	}
+	if u.Ports != nil {
+		if _, err := tx.Exec(`DELETE FROM device_type_ports WHERE device_type_id = ?`, id); err != nil {
+			return nil, err
+		}
+		for _, p := range *u.Ports {
+			if err := insertDeviceTypePort(tx, id, p); err != nil {
+				return nil, err
+			}
+		}
+	}
+	if err := tx.Commit(); err != nil {
+		return nil, err
+	}
+	return s.GetDeviceType(id)
+}
+
+// DeleteDeviceType removes a project-custom row. Built-ins → ErrForbidden.
+// Cross-project → ErrNotFound. Cascades to device_type_ports (FK CASCADE)
+// and SET-NULLs the type_id on any device referencing it.
+func (s *Store) DeleteDeviceType(projectID, id int64) error {
+	cur, err := s.GetDeviceType(id)
+	if err != nil {
+		return err
+	}
+	if cur.BuiltIn {
+		return fmt.Errorf("%w: built-in device types are read-only", ErrForbidden)
+	}
+	if cur.ProjectID == nil || *cur.ProjectID != projectID {
+		return ErrNotFound
+	}
+	if _, err := s.db.Exec(`DELETE FROM device_types WHERE id = ?`, id); err != nil {
+		return err
+	}
+	return nil
+}

internal/db/device_types_test.go

@@ -0,0 +1,283 @@
+package db
+
+import (
+	"errors"
+	"testing"
+)
+
+// -------------------------------------------------------- catalog (seeded)
+
+func TestSeed_BuiltInDeviceTypes(t *testing.T) {
+	s := newTestStore(t)
+	got, err := s.ListBuiltInDeviceTypes()
+	if err != nil {
+		t.Fatalf("list: %v", err)
+	}
+	want := []string{
+		"NAS", "PC", "Mac", "Notebook", "TV", "Soundbar", "Switch", "fritz",
+		"ChromeCast", "SteamLink", "IOx-3", "IOx-6", "IOx-8",
+		"Screen", "Keyboard", "Mouse",
+	}
+	if len(got) != len(want) {
+		t.Fatalf("built-in count = %d, want %d", len(got), len(want))
+	}
+	for i, w := range want {
+		if got[i].Name != w {
+			t.Errorf("[%d] = %q, want %q", i, got[i].Name, w)
+		}
+		if !got[i].BuiltIn {
+			t.Errorf("[%d] %q should be built_in", i, got[i].Name)
+		}
+		if got[i].ProjectID != nil {
+			t.Errorf("[%d] %q should have project_id=nil", i, got[i].Name)
+		}
+	}
+}
+
+func TestSeed_PortProfiles(t *testing.T) {
+	s := newTestStore(t)
+	all, _ := s.ListBuiltInDeviceTypes()
+	byName := map[string]DeviceType{}
+	for _, d := range all {
+		byName[d.Name] = d
+	}
+	cases := map[string]struct {
+		totalPorts int // sum of count across profile rows
+	}{
+		"NAS":        {2},  // Power 1 + RJ45 1
+		"PC":         {5},  // Power 1 + RJ45 1 + HDMI 1 + USB 2
+		"Mac":        {4},  // Power 1 + HDMI 1 + USB 2
+		"Notebook":   {3},  // Power 1 + USB 2
+		"TV":         {3},  // Power 1 + HDMI 2
+		"Soundbar":   {2},  // Power 1 + HDMI 1
+		"Switch":     {6},  // Power 1 + RJ45 5
+		"fritz":      {5},  // Power 1 + RJ45 4
+		"ChromeCast": {2},  // Power 1 + HDMI 1
+		"SteamLink":  {4},  // Power 1 + HDMI 1 + USB 2
+		"IOx-3":      {4},  // Power 1 + USB 3
+		"IOx-6":      {7},  // Power 1 + USB 6
+		"IOx-8":      {9},  // Power 1 + USB 8
+		"Screen":     {2},  // Power 1 + HDMI 1
+		"Keyboard":   {1},  // USB 1
+		"Mouse":      {1},  // USB 1
+	}
+	for name, want := range cases {
+		dt, ok := byName[name]
+		if !ok {
+			t.Errorf("missing built-in %q", name)
+			continue
+		}
+		total := 0
+		for _, p := range dt.Ports {
+			total += p.Count
+		}
+		if total != want.totalPorts {
+			t.Errorf("%s: total ports = %d, want %d", name, total, want.totalPorts)
+		}
+	}
+}
+
+// -------------------------------------------------------- CRUD (custom rows)
+
+func TestCreateDeviceType_CustomBasic(t *testing.T) {
+	s := newTestStore(t)
+	p, _ := s.CreateProject("LOFT", "", "")
+	dt, err := s.CreateDeviceType(p.ID, DeviceTypeCreate{
+		Name: "DigitalCam", Kind: "accessory",
+		Description: "A camera with HDMI out",
+		Ports: []DeviceTypePortCreate{
+			{CableTypeID: 1, LabelPrefix: "Power", Count: 1},
+			{CableTypeID: 3, LabelPrefix: "HDMI", Count: 1, SortOrder: 1},
+		},
+	})
+	if err != nil {
+		t.Fatalf("create: %v", err)
+	}
+	if dt.BuiltIn {
+		t.Errorf("built_in should be false")
+	}
+	if dt.ProjectID == nil || *dt.ProjectID != p.ID {
+		t.Errorf("project_id mismatch: %+v", dt.ProjectID)
+	}
+	if len(dt.Ports) != 2 {
+		t.Errorf("port profile rows = %d, want 2", len(dt.Ports))
+	}
+}
+
+func TestCreateDeviceType_NameClashWithBuiltIn(t *testing.T) {
+	s := newTestStore(t)
+	p, _ := s.CreateProject("LOFT", "", "")
+	_, err := s.CreateDeviceType(p.ID, DeviceTypeCreate{Name: "NAS"})
+	if !errors.Is(err, ErrConflict) {
+		t.Errorf("err = %v, want ErrConflict (NAS is built-in)", err)
+	}
+}
+
+func TestCreateDeviceType_PerProjectUnique(t *testing.T) {
+	s := newTestStore(t)
+	p, _ := s.CreateProject("LOFT", "", "")
+	if _, err := s.CreateDeviceType(p.ID, DeviceTypeCreate{Name: "Foo"}); err != nil {
+		t.Fatalf("first: %v", err)
+	}
+	if _, err := s.CreateDeviceType(p.ID, DeviceTypeCreate{Name: "Foo"}); !errors.Is(err, ErrConflict) {
+		t.Errorf("dup err = %v, want ErrConflict", err)
+	}
+}
+
+func TestUpdateDeviceType_BuiltInForbidden(t *testing.T) {
+	s := newTestStore(t)
+	p, _ := s.CreateProject("LOFT", "", "")
+	all, _ := s.ListBuiltInDeviceTypes()
+	nas := all[0]
+	newName := "renamed"
+	_, err := s.UpdateDeviceType(p.ID, nas.ID, DeviceTypeUpdate{Name: &newName})
+	if !errors.Is(err, ErrForbidden) {
+		t.Errorf("err = %v, want ErrForbidden", err)
+	}
+}
+
+func TestDeleteDeviceType_BuiltInForbidden(t *testing.T) {
+	s := newTestStore(t)
+	p, _ := s.CreateProject("LOFT", "", "")
+	all, _ := s.ListBuiltInDeviceTypes()
+	if err := s.DeleteDeviceType(p.ID, all[0].ID); !errors.Is(err, ErrForbidden) {
+		t.Errorf("err = %v, want ErrForbidden", err)
+	}
+}
+
+func TestUpdateDeviceType_CrossProjectIsNotFound(t *testing.T) {
+	s := newTestStore(t)
+	p1, _ := s.CreateProject("LOFT", "", "")
+	p2, _ := s.CreateProject("OFFICE", "", "")
+	dt, _ := s.CreateDeviceType(p1.ID, DeviceTypeCreate{Name: "Foo"})
+	newName := "bar"
+	if _, err := s.UpdateDeviceType(p2.ID, dt.ID, DeviceTypeUpdate{Name: &newName}); !errors.Is(err, ErrNotFound) {
+		t.Errorf("err = %v, want ErrNotFound", err)
+	}
+}
+
+// -------------------------------------------------------- device + ports seed
+
+func TestCreateDevice_SeedsPortsFromBuiltInType(t *testing.T) {
+	s := newTestStore(t)
+	p, _ := s.CreateProject("LOFT", "", "")
+	all, _ := s.ListBuiltInDeviceTypes()
+	var nasID int64
+	for _, dt := range all {
+		if dt.Name == "NAS" {
+			nasID = dt.ID
+			break
+		}
+	}
+	if nasID == 0 {
+		t.Fatal("NAS not in catalog")
+	}
+	d, err := s.CreateDevice(p.ID, DeviceCreate{
+		Name: "NAS-Loft", TypeID: &nasID,
+		X: 100, Y: 100, Width: 100, Height: 35,
+	})
+	if err != nil {
+		t.Fatalf("create: %v", err)
+	}
+	if d.TypeID == nil || *d.TypeID != nasID {
+		t.Errorf("type_id wrong: %+v", d.TypeID)
+	}
+	ports, _ := s.ListPortsForProject(p.ID)
+	if len(ports) != 2 {
+		t.Fatalf("port count = %d, want 2 (Power + RJ45)", len(ports))
+	}
+	for _, prt := range ports {
+		if prt.YOffset != 35 {
+			t.Errorf("port y_offset = %v, want 35 (bottom edge)", prt.YOffset)
+		}
+		if prt.XOffset <= 0 || prt.XOffset >= 100 {
+			t.Errorf("port x_offset = %v, want between 0 and 100", prt.XOffset)
+		}
+		if prt.Label == nil {
+			t.Errorf("port label = nil, want non-nil (label_prefix is set)")
+		}
+	}
+}
+
+func TestCreateDevice_SeedsPortsForPC_FourGroupsFiveTotal(t *testing.T) {
+	s := newTestStore(t)
+	p, _ := s.CreateProject("LOFT", "", "")
+	all, _ := s.ListBuiltInDeviceTypes()
+	var pcID int64
+	for _, dt := range all {
+		if dt.Name == "PC" {
+			pcID = dt.ID
+			break
+		}
+	}
+	if pcID == 0 {
+		t.Fatal("PC not in catalog")
+	}
+	if _, err := s.CreateDevice(p.ID, DeviceCreate{
+		Name: "Workstation", TypeID: &pcID,
+		X: 0, Y: 0, Width: 100, Height: 35,
+	}); err != nil {
+		t.Fatalf("create: %v", err)
+	}
+	ports, _ := s.ListPortsForProject(p.ID)
+	if len(ports) != 5 {
+		t.Errorf("port count = %d, want 5 (Power+RJ45+HDMI+USB×2)", len(ports))
+	}
+	// USB×2 must produce two labels "USB 1" and "USB 2".
+	usbLabels := map[string]bool{}
+	for _, prt := range ports {
+		if prt.Label != nil && (*prt.Label == "USB 1" || *prt.Label == "USB 2") {
+			usbLabels[*prt.Label] = true
+		}
+	}
+	if !usbLabels["USB 1"] || !usbLabels["USB 2"] {
+		t.Errorf("USB labels missing: got %v", usbLabels)
+	}
+}
+
+func TestCreateDevice_NoTypeID_NoPorts(t *testing.T) {
+	s := newTestStore(t)
+	p, _ := s.CreateProject("LOFT", "", "")
+	if _, err := s.CreateDevice(p.ID, DeviceCreate{
+		Name: "Freeform", X: 0, Y: 0, Width: 100, Height: 35,
+	}); err != nil {
+		t.Fatalf("create: %v", err)
+	}
+	ports, _ := s.ListPortsForProject(p.ID)
+	if len(ports) != 0 {
+		t.Errorf("freeform device should have 0 ports, got %d", len(ports))
+	}
+}
+
+func TestCreateDevice_CrossProjectCustomTypeRejected(t *testing.T) {
+	s := newTestStore(t)
+	p1, _ := s.CreateProject("LOFT", "", "")
+	p2, _ := s.CreateProject("OFFICE", "", "")
+	custom, _ := s.CreateDeviceType(p1.ID, DeviceTypeCreate{Name: "Exotic"})
+	_, err := s.CreateDevice(p2.ID, DeviceCreate{
+		Name: "Wrong", TypeID: &custom.ID,
+		X: 0, Y: 0, Width: 100, Height: 35,
+	})
+	if !errors.Is(err, ErrInvalidInput) {
+		t.Errorf("err = %v, want ErrInvalidInput (cross-project custom type)", err)
+	}
+}
+
+func TestSnapshot_IncludesPorts(t *testing.T) {
+	s := newTestStore(t)
+	p, _ := s.CreateProject("LOFT", "", "")
+	all, _ := s.ListBuiltInDeviceTypes()
+	for _, dt := range all {
+		if dt.Name == "Mac" {
+			_, _ = s.CreateDevice(p.ID, DeviceCreate{
+				Name: "M1", TypeID: &dt.ID,
+				X: 0, Y: 0, Width: 100, Height: 35,
+			})
+			break
+		}
+	}
+	snap, _ := s.Snapshot(p.ID)
+	if len(snap.Ports) != 4 {
+		t.Errorf("snapshot.Ports = %d, want 4 (Mac: Power+HDMI+USB×2)", len(snap.Ports))
+	}
+}

internal/db/frames_devices.go

@@ -166,9 +166,14 @@ func (s *Store) DeleteFrame(projectID, id int64) error {
 // -----------------------------------------------------------------------------
 
 // DeviceCreate is the create-shape. FrameID may be nil ("outside any frame").
+// TypeID may be nil for a freeform device (no auto-seeded ports). If set,
+// the type must be either built-in or a project-custom type belonging to
+// the same project — and CreateDevice seeds the device's ports from the
+// type's port profile in the same transaction.
 type DeviceCreate struct {
 	Name    string
 	FrameID *int64
+	TypeID  *int64
 	Color   string
 	X       float64
 	Y       float64
@@ -179,10 +184,11 @@ type DeviceCreate struct {
 // DeviceUpdate is the partial-update shape. project_id deliberately not
 // settable. FrameID is *(*int64) so callers can distinguish "leave as-is"
 // (nil) from "set to NULL" (&nil) — Go syntax: pass a *(*int64) where the
-// inner pointer is nil to clear.
+// inner pointer is nil to clear. TypeID uses the same FrameRef tri-state.
 type DeviceUpdate struct {
 	Name      *string
 	FrameID   FrameRef // see FrameRef below
+	TypeID    FrameRef // tri-state for type_id: same shape as FrameRef
 	Color     *string
 	X         *float64
 	Y         *float64
@@ -201,7 +207,11 @@ type FrameRef struct {
 }
 
 // CreateDevice inserts a new device. FrameID, if provided, must reference
-// a frame in the same project.
+// a frame in the same project. TypeID, if provided, must reference a
+// built-in or a project-custom device_type in the same project — the
+// store seeds the device's ports from that type's profile in the same
+// transaction so a half-created device (row inserted, ports missing)
+// can never exist.
 func (s *Store) CreateDevice(projectID int64, d DeviceCreate) (*Device, error) {
 	name := strings.TrimSpace(d.Name)
 	if name == "" {
@@ -221,32 +231,62 @@ func (s *Store) CreateDevice(projectID int64, d DeviceCreate) (*Device, error) {
 			return nil, err
 		}
 	}
+	if d.TypeID != nil {
+		dt, err := s.GetDeviceType(*d.TypeID)
+		if err != nil {
+			if errors.Is(err, ErrNotFound) {
+				return nil, fmt.Errorf("%w: device type %d not found", ErrInvalidInput, *d.TypeID)
+			}
+			return nil, err
+		}
+		// Project-custom types must match the device's project. Built-ins
+		// (project_id NULL) are available to every project.
+		if dt.ProjectID != nil && *dt.ProjectID != projectID {
+			return nil, fmt.Errorf("%w: device type %d is custom to another project", ErrInvalidInput, *d.TypeID)
+		}
+	}
 	color := strings.TrimSpace(d.Color)
 	if color == "" {
 		color = "#1e1e1e"
 	}
 
-	res, err := s.db.Exec(
-		`INSERT INTO devices (project_id, frame_id, name, color, x, y, width, height)
-		 VALUES (?, ?, ?, ?, ?, ?, ?, ?)`,
-		projectID, nullableInt64(d.FrameID), name, color, d.X, d.Y, d.Width, d.Height,
+	tx, err := s.db.Begin()
+	if err != nil {
+		return nil, err
+	}
+	defer tx.Rollback()
+
+	res, err := tx.Exec(
+		`INSERT INTO devices (project_id, frame_id, type_id, name, color, x, y, width, height)
+		 VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?)`,
+		projectID, nullableInt64(d.FrameID), nullableInt64(d.TypeID),
+		name, color, d.X, d.Y, d.Width, d.Height,
 	)
 	if err != nil {
 		return nil, mapWriteErr(err)
 	}
-	id, _ := res.LastInsertId()
-	return s.GetDevice(projectID, id)
+	deviceID, _ := res.LastInsertId()
+
+	if d.TypeID != nil {
+		if err := s.seedPortsFromType(tx, projectID, deviceID, *d.TypeID, d.Width, d.Height); err != nil {
+			return nil, err
+		}
+	}
+	if err := tx.Commit(); err != nil {
+		return nil, err
+	}
+	return s.GetDevice(projectID, deviceID)
 }
 
 // GetDevice loads a device, project-scoped.
 func (s *Store) GetDevice(projectID, id int64) (*Device, error) {
 	var d Device
-	var frame sql.NullInt64
+	var frame, typeID sql.NullInt64
 	var ex sql.NullString
 	err := s.db.QueryRow(
-		`SELECT id, project_id, frame_id, name, color, x, y, width, height, excalidraw_id, created_at, updated_at
+		`SELECT id, project_id, frame_id, type_id, name, color, x, y, width, height, excalidraw_id, created_at, updated_at
 		 FROM devices WHERE id = ? AND project_id = ?`, id, projectID,
-	).Scan(&d.ID, &d.ProjectID, &frame, &d.Name, &d.Color, &d.X, &d.Y, &d.Width, &d.Height,
+	).Scan(&d.ID, &d.ProjectID, &frame, &typeID, &d.Name, &d.Color, &d.X, &d.Y, &d.Width, &d.Height,
 		&ex, &d.CreatedAt, &d.UpdatedAt)
 	if errors.Is(err, sql.ErrNoRows) {
 		return nil, ErrNotFound
@@ -258,6 +298,10 @@ func (s *Store) GetDevice(projectID, id int64) (*Device, error) {
 		v := frame.Int64
 		d.FrameID = &v
 	}
+	if typeID.Valid {
+		v := typeID.Int64
+		d.TypeID = &v
+	}
 	if ex.Valid {
 		d.ExcalidrawID = &ex.String
 	}
@@ -277,13 +321,13 @@ func (s *Store) ListDevices(projectID int64, frameID *int64) ([]Device, error) {
 	)
 	if frameID != nil {
 		rows, err = s.db.Query(
-			`SELECT id, project_id, frame_id, name, color, x, y, width, height, excalidraw_id, created_at, updated_at
+			`SELECT id, project_id, frame_id, type_id, name, color, x, y, width, height, excalidraw_id, created_at, updated_at
 			 FROM devices WHERE project_id = ? AND frame_id = ? ORDER BY created_at, id`,
 			projectID, *frameID,
 		)
 	} else {
 		rows, err = s.db.Query(
-			`SELECT id, project_id, frame_id, name, color, x, y, width, height, excalidraw_id, created_at, updated_at
+			`SELECT id, project_id, frame_id, type_id, name, color, x, y, width, height, excalidraw_id, created_at, updated_at
 			 FROM devices WHERE project_id = ? ORDER BY created_at, id`,
 			projectID,
 		)
@@ -295,9 +339,9 @@ func (s *Store) ListDevices(projectID int64, frameID *int64) ([]Device, error) {
 	out := []Device{}
 	for rows.Next() {
 		var d Device
-		var frame sql.NullInt64
+		var frame, typeID sql.NullInt64
 		var ex sql.NullString
-		if err := rows.Scan(&d.ID, &d.ProjectID, &frame, &d.Name, &d.Color, &d.X, &d.Y, &d.Width, &d.Height,
+		if err := rows.Scan(&d.ID, &d.ProjectID, &frame, &typeID, &d.Name, &d.Color, &d.X, &d.Y, &d.Width, &d.Height,
 			&ex, &d.CreatedAt, &d.UpdatedAt); err != nil {
 			return nil, err
 		}
@@ -305,6 +349,10 @@ func (s *Store) ListDevices(projectID int64, frameID *int64) ([]Device, error) {
 			v := frame.Int64
 			d.FrameID = &v
 		}
+		if typeID.Valid {
+			v := typeID.Int64
+			d.TypeID = &v
+		}
 		if ex.Valid {
 			d.ExcalidrawID = &ex.String
 		}
@@ -363,11 +411,27 @@ func (s *Store) UpdateDevice(projectID, id int64, u DeviceUpdate) (*Device, erro
 		}
 		cur.FrameID = u.FrameID.ID
 	}
+	if u.TypeID.Set {
+		if u.TypeID.ID != nil {
+			dt, err := s.GetDeviceType(*u.TypeID.ID)
+			if err != nil {
+				if errors.Is(err, ErrNotFound) {
+					return nil, fmt.Errorf("%w: device type %d not found", ErrInvalidInput, *u.TypeID.ID)
+				}
+				return nil, err
+			}
+			if dt.ProjectID != nil && *dt.ProjectID != projectID {
+				return nil, fmt.Errorf("%w: device type %d is custom to another project", ErrInvalidInput, *u.TypeID.ID)
+			}
+		}
+		cur.TypeID = u.TypeID.ID
+	}
 	if _, err := s.db.Exec(
 		`UPDATE devices
-		 SET frame_id = ?, name = ?, color = ?, x = ?, y = ?, width = ?, height = ?, updated_at = datetime('now')
+		 SET frame_id = ?, type_id = ?, name = ?, color = ?, x = ?, y = ?, width = ?, height = ?, updated_at = datetime('now')
 		 WHERE id = ? AND project_id = ?`,
-		nullableInt64(cur.FrameID), cur.Name, cur.Color, cur.X, cur.Y, cur.Width, cur.Height, id, projectID,
+		nullableInt64(cur.FrameID), nullableInt64(cur.TypeID),
+		cur.Name, cur.Color, cur.X, cur.Y, cur.Width, cur.Height, id, projectID,
 	); err != nil {
 		return nil, mapWriteErr(err)
 	}

internal/db/io_markers.go

@@ -0,0 +1,180 @@
+package db
+
+import (
+	"database/sql"
+	"errors"
+	"fmt"
+	"strings"
+)
+
+// IOMarker is a wall-outlet terminator inside a project. Mostly Power
+// by convention; the schema doesn't enforce it.
+type IOMarker struct {
+	ID            int64   `json:"id"`
+	ProjectID     int64   `json:"project_id"`
+	FrameID       *int64  `json:"frame_id"`
+	Label         string  `json:"label"`
+	X             float64 `json:"x"`
+	Y             float64 `json:"y"`
+	ExcalidrawID  *string `json:"excalidraw_id,omitempty"`
+	CreatedAt     string  `json:"created_at"`
+	UpdatedAt     string  `json:"updated_at"`
+}
+
+// IOMarkerCreate is the create-shape.
+type IOMarkerCreate struct {
+	FrameID *int64
+	Label   string
+	X       float64
+	Y       float64
+}
+
+// IOMarkerUpdate is the partial-update shape. project_id deliberately not
+// settable; frame_id uses the same tri-state shape as DeviceUpdate.FrameID.
+type IOMarkerUpdate struct {
+	Label   *string
+	FrameID FrameRef
+	X       *float64
+	Y       *float64
+}
+
+// CreateIOMarker inserts a new IO marker. If frame_id is set, it must
+// reference a frame in the same project.
+func (s *Store) CreateIOMarker(projectID int64, m IOMarkerCreate) (*IOMarker, error) {
+	label := strings.TrimSpace(m.Label)
+	if label == "" {
+		label = "IO"
+	}
+	if _, err := s.GetProject(projectID); err != nil {
+		return nil, err
+	}
+	if m.FrameID != nil {
+		if _, err := s.GetFrame(projectID, *m.FrameID); err != nil {
+			if errors.Is(err, ErrNotFound) {
+				return nil, fmt.Errorf("%w: frame_id %d not in project %d", ErrInvalidInput, *m.FrameID, projectID)
+			}
+			return nil, err
+		}
+	}
+	res, err := s.db.Exec(
+		`INSERT INTO io_markers (project_id, frame_id, label, x, y)
+		 VALUES (?, ?, ?, ?, ?)`,
+		projectID, nullableInt64(m.FrameID), label, m.X, m.Y,
+	)
+	if err != nil {
+		return nil, mapWriteErr(err)
+	}
+	id, _ := res.LastInsertId()
+	return s.GetIOMarker(projectID, id)
+}
+
+// GetIOMarker loads an IO marker, project-scoped.
+func (s *Store) GetIOMarker(projectID, id int64) (*IOMarker, error) {
+	var m IOMarker
+	var frame sql.NullInt64
+	var ex sql.NullString
+	err := s.db.QueryRow(
+		`SELECT id, project_id, frame_id, label, x, y, excalidraw_id, created_at, updated_at
+		 FROM io_markers WHERE id = ? AND project_id = ?`, id, projectID,
+	).Scan(&m.ID, &m.ProjectID, &frame, &m.Label, &m.X, &m.Y, &ex, &m.CreatedAt, &m.UpdatedAt)
+	if errors.Is(err, sql.ErrNoRows) {
+		return nil, ErrNotFound
+	}
+	if err != nil {
+		return nil, err
+	}
+	if frame.Valid {
+		v := frame.Int64
+		m.FrameID = &v
+	}
+	if ex.Valid {
+		m.ExcalidrawID = &ex.String
+	}
+	return &m, nil
+}
+
+// ListIOMarkers returns every IO marker in a project, ordered by creation.
+func (s *Store) ListIOMarkers(projectID int64) ([]IOMarker, error) {
+	rows, err := s.db.Query(
+		`SELECT id, project_id, frame_id, label, x, y, excalidraw_id, created_at, updated_at
+		 FROM io_markers WHERE project_id = ? ORDER BY created_at, id`, projectID,
+	)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	out := []IOMarker{}
+	for rows.Next() {
+		var m IOMarker
+		var frame sql.NullInt64
+		var ex sql.NullString
+		if err := rows.Scan(&m.ID, &m.ProjectID, &frame, &m.Label, &m.X, &m.Y,
+			&ex, &m.CreatedAt, &m.UpdatedAt); err != nil {
+			return nil, err
+		}
+		if frame.Valid {
+			v := frame.Int64
+			m.FrameID = &v
+		}
+		if ex.Valid {
+			m.ExcalidrawID = &ex.String
+		}
+		out = append(out, m)
+	}
+	return out, rows.Err()
+}
+
+// UpdateIOMarker applies a partial update. project_id is locked; frame_id
+// tri-state mirrors DeviceUpdate.FrameID.
+func (s *Store) UpdateIOMarker(projectID, id int64, u IOMarkerUpdate) (*IOMarker, error) {
+	cur, err := s.GetIOMarker(projectID, id)
+	if err != nil {
+		return nil, err
+	}
+	if u.Label != nil {
+		v := strings.TrimSpace(*u.Label)
+		if v == "" {
+			return nil, fmt.Errorf("%w: label cannot be empty", ErrInvalidInput)
+		}
+		cur.Label = v
+	}
+	if u.X != nil {
+		cur.X = *u.X
+	}
+	if u.Y != nil {
+		cur.Y = *u.Y
+	}
+	if u.FrameID.Set {
+		if u.FrameID.ID != nil {
+			if _, err := s.GetFrame(projectID, *u.FrameID.ID); err != nil {
+				if errors.Is(err, ErrNotFound) {
+					return nil, fmt.Errorf("%w: frame_id %d not in project %d", ErrInvalidInput, *u.FrameID.ID, projectID)
+				}
+				return nil, err
+			}
+		}
+		cur.FrameID = u.FrameID.ID
+	}
+	if _, err := s.db.Exec(
+		`UPDATE io_markers
+		 SET frame_id = ?, label = ?, x = ?, y = ?, updated_at = datetime('now')
+		 WHERE id = ? AND project_id = ?`,
+		nullableInt64(cur.FrameID), cur.Label, cur.X, cur.Y, id, projectID,
+	); err != nil {
+		return nil, mapWriteErr(err)
+	}
+	return s.GetIOMarker(projectID, id)
+}
+
+// DeleteIOMarker removes an IO marker from a project.
+func (s *Store) DeleteIOMarker(projectID, id int64) error {
+	if _, err := s.GetIOMarker(projectID, id); err != nil {
+		return err
+	}
+	if _, err := s.db.Exec(
+		`DELETE FROM io_markers WHERE id = ? AND project_id = ?`, id, projectID,
+	); err != nil {
+		return err
+	}
+	return nil
+}

internal/db/io_markers_test.go

@@ -0,0 +1,113 @@
+package db
+
+import (
+	"errors"
+	"testing"
+)
+
+func TestCreateIOMarker_DefaultsLabel(t *testing.T) {
+	s := newTestStore(t)
+	p, _ := s.CreateProject("LOFT", "", "")
+	m, err := s.CreateIOMarker(p.ID, IOMarkerCreate{X: 10, Y: 20})
+	if err != nil {
+		t.Fatalf("create: %v", err)
+	}
+	if m.Label != "IO" {
+		t.Errorf("default label = %q, want IO", m.Label)
+	}
+	if m.FrameID != nil {
+		t.Errorf("frame_id = %v, want nil", m.FrameID)
+	}
+}
+
+func TestCreateIOMarker_CustomLabel(t *testing.T) {
+	s := newTestStore(t)
+	p, _ := s.CreateProject("LOFT", "", "")
+	m, err := s.CreateIOMarker(p.ID, IOMarkerCreate{Label: "Wall A", X: 0, Y: 0})
+	if err != nil {
+		t.Fatalf("create: %v", err)
+	}
+	if m.Label != "Wall A" {
+		t.Errorf("label = %q, want Wall A", m.Label)
+	}
+}
+
+func TestCreateIOMarker_CrossProjectFrameRejected(t *testing.T) {
+	s := newTestStore(t)
+	p1, _ := s.CreateProject("LOFT", "", "")
+	p2, _ := s.CreateProject("OFFICE", "", "")
+	f2, _ := s.CreateFrame(p2.ID, FrameCreate{Name: "desk", Width: 100, Height: 50})
+	_, err := s.CreateIOMarker(p1.ID, IOMarkerCreate{FrameID: &f2.ID, X: 0, Y: 0})
+	if !errors.Is(err, ErrInvalidInput) {
+		t.Errorf("cross-project frame_id should ErrInvalidInput; got %v", err)
+	}
+}
+
+func TestGetIOMarker_WrongProjectIsNotFound(t *testing.T) {
+	s := newTestStore(t)
+	p1, _ := s.CreateProject("LOFT", "", "")
+	p2, _ := s.CreateProject("OFFICE", "", "")
+	m, _ := s.CreateIOMarker(p1.ID, IOMarkerCreate{X: 0, Y: 0})
+	if _, err := s.GetIOMarker(p2.ID, m.ID); !errors.Is(err, ErrNotFound) {
+		t.Errorf("cross-project GetIOMarker should be ErrNotFound; got %v", err)
+	}
+}
+
+func TestUpdateIOMarker_FrameIDTriState(t *testing.T) {
+	s := newTestStore(t)
+	p, _ := s.CreateProject("LOFT", "", "")
+	f, _ := s.CreateFrame(p.ID, FrameCreate{Name: "desk", Width: 100, Height: 50})
+	m, _ := s.CreateIOMarker(p.ID, IOMarkerCreate{FrameID: &f.ID, X: 0, Y: 0})
+
+	// Leave alone — passing a different X must not clear frame_id.
+	nx := 99.0
+	u1, _ := s.UpdateIOMarker(p.ID, m.ID, IOMarkerUpdate{X: &nx})
+	if u1.FrameID == nil || *u1.FrameID != f.ID {
+		t.Errorf("frame_id should still be set (Set=false); got %v", u1.FrameID)
+	}
+
+	// Clear.
+	u2, _ := s.UpdateIOMarker(p.ID, m.ID, IOMarkerUpdate{FrameID: FrameRef{Set: true, ID: nil}})
+	if u2.FrameID != nil {
+		t.Errorf("frame_id should be nil after clear; got %v", *u2.FrameID)
+	}
+}
+
+func TestDeleteFrame_SetsIOMarkerFrameIDToNull(t *testing.T) {
+	s := newTestStore(t)
+	p, _ := s.CreateProject("LOFT", "", "")
+	f, _ := s.CreateFrame(p.ID, FrameCreate{Name: "desk", Width: 800, Height: 600})
+	m, _ := s.CreateIOMarker(p.ID, IOMarkerCreate{FrameID: &f.ID, X: 10, Y: 20})
+	if m.FrameID == nil {
+		t.Fatalf("pre-condition: io marker should have frame_id")
+	}
+	if err := s.DeleteFrame(p.ID, f.ID); err != nil {
+		t.Fatalf("delete frame: %v", err)
+	}
+	m2, _ := s.GetIOMarker(p.ID, m.ID)
+	if m2.FrameID != nil {
+		t.Errorf("io marker frame_id post-delete = %v, want nil (SET NULL)", m2.FrameID)
+	}
+}
+
+func TestSnapshot_PopulatesIOMarkers(t *testing.T) {
+	s := newTestStore(t)
+	p, _ := s.CreateProject("LOFT", "", "")
+	_, _ = s.CreateIOMarker(p.ID, IOMarkerCreate{Label: "Wall A", X: 10, Y: 20})
+	_, _ = s.CreateIOMarker(p.ID, IOMarkerCreate{Label: "UPS rear", X: 100, Y: 200})
+	snap, err := s.Snapshot(p.ID)
+	if err != nil {
+		t.Fatalf("snapshot: %v", err)
+	}
+	if len(snap.IOMarkers) != 2 {
+		t.Errorf("io_markers len = %d, want 2", len(snap.IOMarkers))
+	}
+}
+
+func TestDeleteIOMarker_NotFound(t *testing.T) {
+	s := newTestStore(t)
+	p, _ := s.CreateProject("LOFT", "", "")
+	if err := s.DeleteIOMarker(p.ID, 999); !errors.Is(err, ErrNotFound) {
+		t.Errorf("got %v, want ErrNotFound", err)
+	}
+}

internal/db/migrations/002_device_catalog.sql

@@ -0,0 +1,167 @@
+-- mCables v4 device-type catalog. See docs/design.md §2.1 + §2.2.
+
+-- v4 — device-type catalog. Built-in types live globally (project_id NULL).
+-- Per-project custom types use project_id = X.
+CREATE TABLE device_types (
+    id              INTEGER PRIMARY KEY,
+    project_id      INTEGER REFERENCES projects(id) ON DELETE CASCADE,
+    name            TEXT NOT NULL,
+    kind            TEXT NOT NULL DEFAULT 'generic',
+    icon            TEXT,
+    description     TEXT NOT NULL DEFAULT '',
+    built_in        INTEGER NOT NULL DEFAULT 0,
+    created_at      TEXT NOT NULL DEFAULT (datetime('now')),
+    updated_at      TEXT NOT NULL DEFAULT (datetime('now')),
+    UNIQUE (project_id, name)
+);
+CREATE INDEX device_types_project_idx ON device_types(project_id);
+
+-- v4 — port profile per device type. Used to seed ports when a device
+-- of that type is created.
+CREATE TABLE device_type_ports (
+    id              INTEGER PRIMARY KEY,
+    device_type_id  INTEGER NOT NULL REFERENCES device_types(id) ON DELETE CASCADE,
+    cable_type_id   INTEGER NOT NULL REFERENCES cable_types(id)  ON DELETE RESTRICT,
+    label_prefix    TEXT NOT NULL DEFAULT '',
+    count           INTEGER NOT NULL DEFAULT 1 CHECK (count >= 1),
+    edge            TEXT NOT NULL DEFAULT 'bottom' CHECK (edge IN ('top','bottom','left','right')),
+    sort_order      INTEGER NOT NULL DEFAULT 0
+);
+CREATE INDEX device_type_ports_type_idx ON device_type_ports(device_type_id);
+
+-- v4 — devices gain a nullable type_id. SET NULL on type-delete so we
+-- never cascade-delete a device the user still wants.
+ALTER TABLE devices ADD COLUMN type_id INTEGER
+    REFERENCES device_types(id) ON DELETE SET NULL;
+CREATE INDEX devices_type_idx ON devices(type_id);
+
+-- Seed the 14 built-in device types.
+-- project_id stays NULL → built-in. The trio Screen / Keyboard / Mouse
+-- was added in v4.1 to support the Home Office setup template (slice 6).
+INSERT INTO device_types (name, kind, built_in, description) VALUES
+    ('NAS',        'storage',   1, 'Network-attached storage'),
+    ('PC',         'compute',   1, 'Desktop PC / workstation'),
+    ('Mac',        'compute',   1, 'Mac (mini / studio / desktop)'),
+    ('Notebook',   'compute',   1, 'Laptop / notebook'),
+    ('TV',         'display',   1, 'Television'),
+    ('Soundbar',   'audio',     1, 'Soundbar / AV receiver'),
+    ('Switch',     'network',   1, 'Ethernet switch'),
+    ('fritz',      'network',   1, 'AVM Fritz!Box router'),
+    ('ChromeCast', 'display',   1, 'ChromeCast / streaming stick'),
+    ('SteamLink',  'compute',   1, 'Steam Link / dedicated streaming box'),
+    ('IOx-3',      'hub',       1, 'USB hub with 3 downstream ports'),
+    ('IOx-6',      'hub',       1, 'USB hub with 6 downstream ports'),
+    ('IOx-8',      'hub',       1, 'USB hub with 8 downstream ports'),
+    ('Screen',     'display',   1, 'External monitor / display'),
+    ('Keyboard',   'accessory', 1, 'Keyboard'),
+    ('Mouse',      'accessory', 1, 'Mouse / pointing device');
+
+-- Now seed device_type_ports. Each row references its device_type by
+-- (SELECT id FROM device_types WHERE name = ? AND project_id IS NULL).
+--
+-- cable_types ids come from the 001 seed in fixed order:
+--   1=Power, 2=USB, 3=HDMI, 4=DP, 5=RJ45
+--
+-- label_prefix is what the seeder appends a 1..N suffix to when count>1.
+-- Default edge is 'bottom'; sort_order positions the port-types from
+-- left to right along that edge.
+
+-- NAS: Power × 1, RJ45 × 1
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 1, 'Power', 1, 'bottom', 0 FROM device_types WHERE name='NAS' AND project_id IS NULL;
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 5, 'RJ45',  1, 'bottom', 1 FROM device_types WHERE name='NAS' AND project_id IS NULL;
+
+-- PC: Power × 1, RJ45 × 1, HDMI × 1, USB × 2
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 1, 'Power', 1, 'bottom', 0 FROM device_types WHERE name='PC' AND project_id IS NULL;
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 5, 'RJ45',  1, 'bottom', 1 FROM device_types WHERE name='PC' AND project_id IS NULL;
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 3, 'HDMI',  1, 'bottom', 2 FROM device_types WHERE name='PC' AND project_id IS NULL;
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 2, 'USB',   2, 'bottom', 3 FROM device_types WHERE name='PC' AND project_id IS NULL;
+
+-- Mac: Power × 1, HDMI × 1, USB × 2
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 1, 'Power', 1, 'bottom', 0 FROM device_types WHERE name='Mac' AND project_id IS NULL;
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 3, 'HDMI',  1, 'bottom', 1 FROM device_types WHERE name='Mac' AND project_id IS NULL;
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 2, 'USB',   2, 'bottom', 2 FROM device_types WHERE name='Mac' AND project_id IS NULL;
+
+-- Notebook: Power × 1, USB × 2
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 1, 'Power', 1, 'bottom', 0 FROM device_types WHERE name='Notebook' AND project_id IS NULL;
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 2, 'USB',   2, 'bottom', 1 FROM device_types WHERE name='Notebook' AND project_id IS NULL;
+
+-- TV: Power × 1, HDMI × 2
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 1, 'Power', 1, 'bottom', 0 FROM device_types WHERE name='TV' AND project_id IS NULL;
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 3, 'HDMI',  2, 'bottom', 1 FROM device_types WHERE name='TV' AND project_id IS NULL;
+
+-- Soundbar: Power × 1, HDMI × 1
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 1, 'Power', 1, 'bottom', 0 FROM device_types WHERE name='Soundbar' AND project_id IS NULL;
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 3, 'HDMI',  1, 'bottom', 1 FROM device_types WHERE name='Soundbar' AND project_id IS NULL;
+
+-- Switch: Power × 1, RJ45 × 5
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 1, 'Power', 1, 'bottom', 0 FROM device_types WHERE name='Switch' AND project_id IS NULL;
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 5, 'RJ45',  5, 'bottom', 1 FROM device_types WHERE name='Switch' AND project_id IS NULL;
+
+-- fritz: Power × 1, RJ45 × 4
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 1, 'Power', 1, 'bottom', 0 FROM device_types WHERE name='fritz' AND project_id IS NULL;
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 5, 'RJ45',  4, 'bottom', 1 FROM device_types WHERE name='fritz' AND project_id IS NULL;
+
+-- ChromeCast: Power × 1, HDMI × 1
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 1, 'Power', 1, 'bottom', 0 FROM device_types WHERE name='ChromeCast' AND project_id IS NULL;
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 3, 'HDMI',  1, 'bottom', 1 FROM device_types WHERE name='ChromeCast' AND project_id IS NULL;
+
+-- SteamLink: Power × 1, HDMI × 1, USB × 2
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 1, 'Power', 1, 'bottom', 0 FROM device_types WHERE name='SteamLink' AND project_id IS NULL;
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 3, 'HDMI',  1, 'bottom', 1 FROM device_types WHERE name='SteamLink' AND project_id IS NULL;
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 2, 'USB',   2, 'bottom', 2 FROM device_types WHERE name='SteamLink' AND project_id IS NULL;
+
+-- IOx-3: Power × 1, USB × 3
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 1, 'Power', 1, 'bottom', 0 FROM device_types WHERE name='IOx-3' AND project_id IS NULL;
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 2, 'USB',   3, 'bottom', 1 FROM device_types WHERE name='IOx-3' AND project_id IS NULL;
+
+-- IOx-6: Power × 1, USB × 6
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 1, 'Power', 1, 'bottom', 0 FROM device_types WHERE name='IOx-6' AND project_id IS NULL;
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 2, 'USB',   6, 'bottom', 1 FROM device_types WHERE name='IOx-6' AND project_id IS NULL;
+
+-- IOx-8: Power × 1, USB × 8
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 1, 'Power', 1, 'bottom', 0 FROM device_types WHERE name='IOx-8' AND project_id IS NULL;
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 2, 'USB',   8, 'bottom', 1 FROM device_types WHERE name='IOx-8' AND project_id IS NULL;
+
+-- Screen: Power × 1, HDMI × 1 (v4.1)
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 1, 'Power', 1, 'bottom', 0 FROM device_types WHERE name='Screen' AND project_id IS NULL;
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 3, 'HDMI',  1, 'bottom', 1 FROM device_types WHERE name='Screen' AND project_id IS NULL;
+
+-- Keyboard: USB × 1 (v4.1)
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 2, 'USB',   1, 'bottom', 0 FROM device_types WHERE name='Keyboard' AND project_id IS NULL;
+
+-- Mouse: USB × 1 (v4.1)
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 2, 'USB',   1, 'bottom', 0 FROM device_types WHERE name='Mouse' AND project_id IS NULL;

internal/db/migrations/003_connection_requirements.sql

@@ -0,0 +1,34 @@
+-- mCables v4.1 connection requirements + solver-owned cable flag.
+-- See docs/design.md §2.1 + §2 connection_requirements + §5b.3.
+
+-- The solver's input: "device A must connect to device B via cable type T".
+-- Many per device. (from, to) is normalised on insert as
+-- (pair_lo, pair_hi) = (MIN(from, to), MAX(from, to)) so (A,B,T) and (B,A,T)
+-- can't coexist (UNIQUE enforces it).
+CREATE TABLE connection_requirements (
+    id                       INTEGER PRIMARY KEY,
+    project_id               INTEGER NOT NULL REFERENCES projects(id) ON DELETE CASCADE,
+    from_device_id           INTEGER NOT NULL REFERENCES devices(id) ON DELETE CASCADE,
+    to_device_id             INTEGER NOT NULL REFERENCES devices(id) ON DELETE CASCADE,
+    preferred_cable_type_id  INTEGER REFERENCES cable_types(id) ON DELETE SET NULL,
+    must_connect             INTEGER NOT NULL DEFAULT 1 CHECK (must_connect IN (0, 1)),
+    notes                    TEXT NOT NULL DEFAULT '',
+    pair_lo                  INTEGER NOT NULL,
+    pair_hi                  INTEGER NOT NULL,
+    created_at               TEXT NOT NULL DEFAULT (datetime('now')),
+    updated_at               TEXT NOT NULL DEFAULT (datetime('now')),
+    CHECK (from_device_id != to_device_id),
+    UNIQUE (project_id, pair_lo, pair_hi, preferred_cable_type_id)
+);
+CREATE INDEX conn_reqs_project_idx ON connection_requirements(project_id);
+CREATE INDEX conn_reqs_pair_idx    ON connection_requirements(project_id, pair_lo, pair_hi);
+CREATE INDEX conn_reqs_from_idx    ON connection_requirements(from_device_id);
+CREATE INDEX conn_reqs_to_idx      ON connection_requirements(to_device_id);
+
+-- Solver-owned cable flag (§5b.3): 1 = the solver placed this cable,
+-- replaceable on re-solve. 0 = m hand-drew it, left alone by the solver.
+-- Slice 6 ships the solver that writes auto=1; slice 7 ships hand-drawn
+-- cable creation that writes auto=0.
+ALTER TABLE cables ADD COLUMN auto INTEGER NOT NULL DEFAULT 0
+    CHECK (auto IN (0, 1));
+CREATE INDEX cables_auto_idx ON cables(auto);

internal/db/migrations/004_setup_templates.sql

@@ -0,0 +1,157 @@
+-- mCables v4.1 setup templates. See docs/design.md §2.4.
+--
+-- A template is a named recipe of (device_types + requirements) that
+-- bootstraps a project from blank to solver-ready in one apply call.
+
+CREATE TABLE setup_templates (
+    id              INTEGER PRIMARY KEY,
+    name            TEXT NOT NULL UNIQUE,
+    description     TEXT NOT NULL DEFAULT '',
+    built_in        INTEGER NOT NULL DEFAULT 0,
+    created_at      TEXT NOT NULL DEFAULT (datetime('now')),
+    updated_at      TEXT NOT NULL DEFAULT (datetime('now'))
+);
+
+CREATE TABLE setup_template_devices (
+    id              INTEGER PRIMARY KEY,
+    template_id     INTEGER NOT NULL REFERENCES setup_templates(id) ON DELETE CASCADE,
+    device_type_id  INTEGER NOT NULL REFERENCES device_types(id)    ON DELETE RESTRICT,
+    suggested_name  TEXT,
+    sort_order      INTEGER NOT NULL DEFAULT 0
+);
+CREATE INDEX setup_template_devices_template_idx ON setup_template_devices(template_id);
+
+CREATE TABLE setup_template_requirements (
+    id                       INTEGER PRIMARY KEY,
+    template_id              INTEGER NOT NULL REFERENCES setup_templates(id) ON DELETE CASCADE,
+    from_template_device_id  INTEGER NOT NULL REFERENCES setup_template_devices(id) ON DELETE CASCADE,
+    to_template_device_id    INTEGER NOT NULL REFERENCES setup_template_devices(id) ON DELETE CASCADE,
+    preferred_cable_type_id  INTEGER REFERENCES cable_types(id) ON DELETE SET NULL,
+    must_connect             INTEGER NOT NULL DEFAULT 1 CHECK (must_connect IN (0, 1)),
+    CHECK (from_template_device_id != to_template_device_id)
+);
+CREATE INDEX setup_template_reqs_template_idx ON setup_template_requirements(template_id);
+
+-- ---------------------------------------------------------------- Living Room
+INSERT INTO setup_templates (name, description, built_in)
+    VALUES ('Living Room', 'TV + Soundbar + ChromeCast, HDMI between them.', 1);
+
+INSERT INTO setup_template_devices (template_id, device_type_id, suggested_name, sort_order)
+    SELECT
+        (SELECT id FROM setup_templates WHERE name='Living Room'),
+        (SELECT id FROM device_types WHERE name='TV' AND project_id IS NULL),
+        'TV', 0;
+INSERT INTO setup_template_devices (template_id, device_type_id, suggested_name, sort_order)
+    SELECT
+        (SELECT id FROM setup_templates WHERE name='Living Room'),
+        (SELECT id FROM device_types WHERE name='Soundbar' AND project_id IS NULL),
+        'Soundbar', 1;
+INSERT INTO setup_template_devices (template_id, device_type_id, suggested_name, sort_order)
+    SELECT
+        (SELECT id FROM setup_templates WHERE name='Living Room'),
+        (SELECT id FROM device_types WHERE name='ChromeCast' AND project_id IS NULL),
+        'ChromeCast', 2;
+
+-- TV ↔ Soundbar (HDMI, must)
+INSERT INTO setup_template_requirements
+    (template_id, from_template_device_id, to_template_device_id, preferred_cable_type_id, must_connect)
+    SELECT
+        (SELECT id FROM setup_templates WHERE name='Living Room'),
+        (SELECT id FROM setup_template_devices WHERE template_id = (SELECT id FROM setup_templates WHERE name='Living Room') AND suggested_name='TV'),
+        (SELECT id FROM setup_template_devices WHERE template_id = (SELECT id FROM setup_templates WHERE name='Living Room') AND suggested_name='Soundbar'),
+        3, 1;
+-- TV ↔ ChromeCast (HDMI, must)
+INSERT INTO setup_template_requirements
+    (template_id, from_template_device_id, to_template_device_id, preferred_cable_type_id, must_connect)
+    SELECT
+        (SELECT id FROM setup_templates WHERE name='Living Room'),
+        (SELECT id FROM setup_template_devices WHERE template_id = (SELECT id FROM setup_templates WHERE name='Living Room') AND suggested_name='TV'),
+        (SELECT id FROM setup_template_devices WHERE template_id = (SELECT id FROM setup_templates WHERE name='Living Room') AND suggested_name='ChromeCast'),
+        3, 1;
+
+-- ---------------------------------------------------------------- Home Office
+INSERT INTO setup_templates (name, description, built_in)
+    VALUES ('Home Office', 'PC + Screen + Keyboard + Mouse. HDMI + USB.', 1);
+
+INSERT INTO setup_template_devices (template_id, device_type_id, suggested_name, sort_order)
+    SELECT
+        (SELECT id FROM setup_templates WHERE name='Home Office'),
+        (SELECT id FROM device_types WHERE name='PC' AND project_id IS NULL),
+        'PC', 0;
+INSERT INTO setup_template_devices (template_id, device_type_id, suggested_name, sort_order)
+    SELECT
+        (SELECT id FROM setup_templates WHERE name='Home Office'),
+        (SELECT id FROM device_types WHERE name='Screen' AND project_id IS NULL),
+        'Screen', 1;
+INSERT INTO setup_template_devices (template_id, device_type_id, suggested_name, sort_order)
+    SELECT
+        (SELECT id FROM setup_templates WHERE name='Home Office'),
+        (SELECT id FROM device_types WHERE name='Keyboard' AND project_id IS NULL),
+        'Keyboard', 2;
+INSERT INTO setup_template_devices (template_id, device_type_id, suggested_name, sort_order)
+    SELECT
+        (SELECT id FROM setup_templates WHERE name='Home Office'),
+        (SELECT id FROM device_types WHERE name='Mouse' AND project_id IS NULL),
+        'Mouse', 3;
+
+-- PC ↔ Screen (HDMI, must)
+INSERT INTO setup_template_requirements
+    (template_id, from_template_device_id, to_template_device_id, preferred_cable_type_id, must_connect)
+    SELECT
+        (SELECT id FROM setup_templates WHERE name='Home Office'),
+        (SELECT id FROM setup_template_devices WHERE template_id = (SELECT id FROM setup_templates WHERE name='Home Office') AND suggested_name='PC'),
+        (SELECT id FROM setup_template_devices WHERE template_id = (SELECT id FROM setup_templates WHERE name='Home Office') AND suggested_name='Screen'),
+        3, 1;
+-- PC ↔ Keyboard (USB, must)
+INSERT INTO setup_template_requirements
+    (template_id, from_template_device_id, to_template_device_id, preferred_cable_type_id, must_connect)
+    SELECT
+        (SELECT id FROM setup_templates WHERE name='Home Office'),
+        (SELECT id FROM setup_template_devices WHERE template_id = (SELECT id FROM setup_templates WHERE name='Home Office') AND suggested_name='PC'),
+        (SELECT id FROM setup_template_devices WHERE template_id = (SELECT id FROM setup_templates WHERE name='Home Office') AND suggested_name='Keyboard'),
+        2, 1;
+-- PC ↔ Mouse (USB, must)
+INSERT INTO setup_template_requirements
+    (template_id, from_template_device_id, to_template_device_id, preferred_cable_type_id, must_connect)
+    SELECT
+        (SELECT id FROM setup_templates WHERE name='Home Office'),
+        (SELECT id FROM setup_template_devices WHERE template_id = (SELECT id FROM setup_templates WHERE name='Home Office') AND suggested_name='PC'),
+        (SELECT id FROM setup_template_devices WHERE template_id = (SELECT id FROM setup_templates WHERE name='Home Office') AND suggested_name='Mouse'),
+        2, 1;
+
+-- ---------------------------------------------------------------- Server Rack
+INSERT INTO setup_templates (name, description, built_in)
+    VALUES ('Server Rack', 'NAS + Switch + fritz. Ethernet trunk + power.', 1);
+
+INSERT INTO setup_template_devices (template_id, device_type_id, suggested_name, sort_order)
+    SELECT
+        (SELECT id FROM setup_templates WHERE name='Server Rack'),
+        (SELECT id FROM device_types WHERE name='NAS' AND project_id IS NULL),
+        'NAS', 0;
+INSERT INTO setup_template_devices (template_id, device_type_id, suggested_name, sort_order)
+    SELECT
+        (SELECT id FROM setup_templates WHERE name='Server Rack'),
+        (SELECT id FROM device_types WHERE name='Switch' AND project_id IS NULL),
+        'Switch', 1;
+INSERT INTO setup_template_devices (template_id, device_type_id, suggested_name, sort_order)
+    SELECT
+        (SELECT id FROM setup_templates WHERE name='Server Rack'),
+        (SELECT id FROM device_types WHERE name='fritz' AND project_id IS NULL),
+        'fritz', 2;
+
+-- NAS ↔ Switch (RJ45, must)
+INSERT INTO setup_template_requirements
+    (template_id, from_template_device_id, to_template_device_id, preferred_cable_type_id, must_connect)
+    SELECT
+        (SELECT id FROM setup_templates WHERE name='Server Rack'),
+        (SELECT id FROM setup_template_devices WHERE template_id = (SELECT id FROM setup_templates WHERE name='Server Rack') AND suggested_name='NAS'),
+        (SELECT id FROM setup_template_devices WHERE template_id = (SELECT id FROM setup_templates WHERE name='Server Rack') AND suggested_name='Switch'),
+        5, 1;
+-- Switch ↔ fritz (RJ45, must)
+INSERT INTO setup_template_requirements
+    (template_id, from_template_device_id, to_template_device_id, preferred_cable_type_id, must_connect)
+    SELECT
+        (SELECT id FROM setup_templates WHERE name='Server Rack'),
+        (SELECT id FROM setup_template_devices WHERE template_id = (SELECT id FROM setup_templates WHERE name='Server Rack') AND suggested_name='Switch'),
+        (SELECT id FROM setup_template_devices WHERE template_id = (SELECT id FROM setup_templates WHERE name='Server Rack') AND suggested_name='fritz'),
+        5, 1;

internal/db/models.go

@@ -34,10 +34,13 @@ type Frame struct {
 }
 
 // Device is a hardware item inside a project, optionally inside a frame.
+// v4: type_id (nullable) lets a device inherit its port profile from a
+// device_types catalog row.
 type Device struct {
 	ID            int64   `json:"id"`
 	ProjectID     int64   `json:"project_id"`
 	FrameID       *int64  `json:"frame_id"`           // nullable: device "outside" any frame
+	TypeID        *int64  `json:"type_id"`            // nullable: freeform device when null
 	Name          string  `json:"name"`
 	Color         string  `json:"color"`
 	X             float64 `json:"x"`
@@ -49,16 +52,171 @@ type Device struct {
 	UpdatedAt     string  `json:"updated_at"`
 }
 
+// DeviceType is a catalog row. Built-in rows have ProjectID nil and
+// BuiltIn true. Project-custom rows have ProjectID set.
+type DeviceType struct {
+	ID          int64             `json:"id"`
+	ProjectID   *int64            `json:"project_id"`
+	Name        string            `json:"name"`
+	Kind        string            `json:"kind"`
+	Icon        *string           `json:"icon,omitempty"`
+	Description string            `json:"description"`
+	BuiltIn     bool              `json:"built_in"`
+	Ports       []DeviceTypePort  `json:"ports"`
+	CreatedAt   string            `json:"created_at"`
+	UpdatedAt   string            `json:"updated_at"`
+}
+
+// DeviceTypePort is a row of a type's port profile. The seeder uses
+// (cable_type_id, count, label_prefix, edge, sort_order) to lay out
+// concrete ports on a freshly-created device.
+type DeviceTypePort struct {
+	ID            int64  `json:"id"`
+	DeviceTypeID  int64  `json:"device_type_id"`
+	CableTypeID   int64  `json:"cable_type_id"`
+	LabelPrefix   string `json:"label_prefix"`
+	Count         int    `json:"count"`
+	Edge          string `json:"edge"`
+	SortOrder     int    `json:"sort_order"`
+}
+
+// Port is a connector on a device. cable_type colour drives the visual
+// rendering; ports are instance-owned even when seeded from a type.
+type Port struct {
+	ID            int64   `json:"id"`
+	ProjectID     int64   `json:"project_id"`
+	DeviceID      int64   `json:"device_id"`
+	TypeID        int64   `json:"type_id"`         // cable type
+	Label         *string `json:"label"`
+	XOffset       float64 `json:"x_offset"`
+	YOffset       float64 `json:"y_offset"`
+	ExcalidrawID  *string `json:"excalidraw_id,omitempty"`
+	CreatedAt     string  `json:"created_at"`
+	UpdatedAt     string  `json:"updated_at"`
+}
+
+// ConnectionRequirement is the solver's per-project input.
+// pair_lo/pair_hi are the ordered (MIN,MAX) of (from, to) so the
+// UNIQUE on (project_id, pair_lo, pair_hi, preferred_cable_type_id)
+// prevents (A,B,T) AND (B,A,T) from coexisting.
+type ConnectionRequirement struct {
+	ID                    int64  `json:"id"`
+	ProjectID             int64  `json:"project_id"`
+	FromDeviceID          int64  `json:"from_device_id"`
+	ToDeviceID            int64  `json:"to_device_id"`
+	PreferredCableTypeID  *int64 `json:"preferred_cable_type_id"`
+	MustConnect           bool   `json:"must_connect"`
+	Notes                 string `json:"notes"`
+	CreatedAt             string `json:"created_at"`
+	UpdatedAt             string `json:"updated_at"`
+}
+
+// Cable is a typed connection. Each endpoint is exactly one of
+// (port, device, io-marker). Auto=true means the solver placed it.
+type Cable struct {
+	ID            int64   `json:"id"`
+	ProjectID     int64   `json:"project_id"`
+	TypeID        int64   `json:"type_id"`
+	Label         *string `json:"label"`
+	FromPortID    *int64  `json:"from_port_id"`
+	FromDeviceID  *int64  `json:"from_device_id"`
+	FromIOID      *int64  `json:"from_io_id"`
+	ToPortID      *int64  `json:"to_port_id"`
+	ToDeviceID    *int64  `json:"to_device_id"`
+	ToIOID        *int64  `json:"to_io_id"`
+	Auto          bool    `json:"auto"`
+	ExcalidrawID  *string `json:"excalidraw_id,omitempty"`
+	CreatedAt     string  `json:"created_at"`
+	UpdatedAt     string  `json:"updated_at"`
+}
+
+// Bundle is a named group of cables that physically run together.
+type Bundle struct {
+	ID         int64   `json:"id"`
+	ProjectID  int64   `json:"project_id"`
+	Name       string  `json:"name"`
+	Auto       bool    `json:"auto"`
+	CableIDs   []int64 `json:"cable_ids"`
+	CreatedAt  string  `json:"created_at"`
+	UpdatedAt  string  `json:"updated_at"`
+}
+
+// SetupTemplate is a named recipe of device-types + requirements.
+type SetupTemplate struct {
+	ID           int64                       `json:"id"`
+	Name         string                      `json:"name"`
+	Description  string                      `json:"description"`
+	BuiltIn      bool                        `json:"built_in"`
+	Devices      []SetupTemplateDevice       `json:"devices"`
+	Requirements []SetupTemplateRequirement  `json:"requirements"`
+	CreatedAt    string                      `json:"created_at"`
+	UpdatedAt    string                      `json:"updated_at"`
+}
+
+type SetupTemplateDevice struct {
+	ID             int64       `json:"id"`
+	TemplateID     int64       `json:"template_id"`
+	DeviceTypeID   int64       `json:"device_type_id"`
+	DeviceType     *DeviceType `json:"device_type,omitempty"`
+	SuggestedName  *string     `json:"suggested_name"`
+	SortOrder      int         `json:"sort_order"`
+}
+
+type SetupTemplateRequirement struct {
+	ID                      int64  `json:"id"`
+	TemplateID              int64  `json:"template_id"`
+	FromTemplateDeviceID    int64  `json:"from_template_device_id"`
+	ToTemplateDeviceID      int64  `json:"to_template_device_id"`
+	PreferredCableTypeID    *int64 `json:"preferred_cable_type_id"`
+	MustConnect             bool   `json:"must_connect"`
+}
+
+// SolveResult is the response shape from POST /api/projects/:pid/solve.
+type SolveResult struct {
+	CablesAdded     []Cable                `json:"cables_added"`
+	CablesKept      []int64                `json:"cables_kept"`
+	CablesRemoved   []int64                `json:"cables_removed"`
+	BundlesAdded    []Bundle               `json:"bundles_added"`
+	BundlesRemoved  []int64                `json:"bundles_removed"`
+	Unsatisfied     []UnsatisfiedReq       `json:"unsatisfied"`
+	Warnings        []string               `json:"warnings"`
+}
+
+type UnsatisfiedReq struct {
+	RequirementID int64  `json:"requirement_id"`
+	Reason        string `json:"reason"`
+	WhichSide     string `json:"which_side,omitempty"` // "from" | "to" | "" when both/neither
+	CableType     string `json:"cable_type,omitempty"`  // when known
+}
+
+// ApplyTemplateResult is the response from POST /apply-template.
+type ApplyTemplateResult struct {
+	DevicesAdded         []Device                `json:"devices_added"`
+	RequirementsAdded    []ConnectionRequirement `json:"requirements_added"`
+	SkippedDevices       []SkippedTemplateDevice `json:"skipped_devices"`
+	RequirementsSkipped  []SkippedTemplateReq    `json:"requirements_skipped"`
+}
+
+type SkippedTemplateDevice struct {
+	TemplateDeviceID int64  `json:"template_device_id"`
+	Reason           string `json:"reason"`
+}
+type SkippedTemplateReq struct {
+	TemplateRequirementID int64  `json:"template_requirement_id"`
+	Reason                string `json:"reason"`
+}
+
 // Snapshot is the editor's one-shot loader payload for a single project.
 // Arrays for collections still gated by future slices stay non-nil [] so
 // JSON encodes as [] not null.
 type Snapshot struct {
-	Project    Project     `json:"project"`
-	Frames     []Frame     `json:"frames"`
-	Devices    []Device    `json:"devices"`
-	Ports      []any       `json:"ports"`
-	Cables     []any       `json:"cables"`
-	IOMarkers  []any       `json:"io_markers"`
-	Bundles    []any       `json:"bundles"`
-	CableTypes []CableType `json:"cable_types"`
+	Project                Project                 `json:"project"`
+	Frames                 []Frame                 `json:"frames"`
+	Devices                []Device                `json:"devices"`
+	Ports                  []Port                  `json:"ports"`
+	Cables                 []Cable                 `json:"cables"`
+	IOMarkers              []IOMarker              `json:"io_markers"`
+	Bundles                []Bundle                `json:"bundles"`
+	CableTypes             []CableType             `json:"cable_types"`
+	ConnectionRequirements []ConnectionRequirement `json:"connection_requirements"`
 }

internal/db/ports.go

@@ -0,0 +1,359 @@
+package db
+
+import (
+	"database/sql"
+	"errors"
+	"fmt"
+	"strings"
+)
+
+// PortCreate is the create-shape for POST /api/projects/:pid/devices/:id/ports.
+type PortCreate struct {
+	TypeID  int64
+	Label   string
+	XOffset float64
+	YOffset float64
+}
+
+// PortUpdate is the partial-update shape.
+type PortUpdate struct {
+	TypeID  *int64
+	Label   *string
+	XOffset *float64
+	YOffset *float64
+}
+
+// CreatePort inserts a port on a device. The device must exist in the
+// project; the cable type must exist globally.
+func (s *Store) CreatePort(projectID, deviceID int64, p PortCreate) (*Port, error) {
+	if _, err := s.GetDevice(projectID, deviceID); err != nil {
+		return nil, err
+	}
+	if _, err := s.GetCableType(p.TypeID); err != nil {
+		if errors.Is(err, ErrNotFound) {
+			return nil, fmt.Errorf("%w: cable type %d not found", ErrInvalidInput, p.TypeID)
+		}
+		return nil, err
+	}
+	label := strings.TrimSpace(p.Label)
+	var labelArg any
+	if label != "" {
+		labelArg = label
+	}
+	res, err := s.db.Exec(
+		`INSERT INTO ports (project_id, device_id, type_id, label, x_offset, y_offset)
+		 VALUES (?, ?, ?, ?, ?, ?)`,
+		projectID, deviceID, p.TypeID, labelArg, p.XOffset, p.YOffset,
+	)
+	if err != nil {
+		return nil, mapWriteErr(err)
+	}
+	id, _ := res.LastInsertId()
+	return s.GetPort(projectID, id)
+}
+
+// GetPort loads a port by id, project-scoped.
+func (s *Store) GetPort(projectID, id int64) (*Port, error) {
+	var p Port
+	var label, ex sql.NullString
+	err := s.db.QueryRow(
+		`SELECT id, project_id, device_id, type_id, label, x_offset, y_offset,
+		        excalidraw_id, created_at, updated_at
+		 FROM ports WHERE id = ? AND project_id = ?`, id, projectID,
+	).Scan(&p.ID, &p.ProjectID, &p.DeviceID, &p.TypeID, &label,
+		&p.XOffset, &p.YOffset, &ex, &p.CreatedAt, &p.UpdatedAt)
+	if errors.Is(err, sql.ErrNoRows) {
+		return nil, ErrNotFound
+	}
+	if err != nil {
+		return nil, err
+	}
+	if label.Valid {
+		v := label.String
+		p.Label = &v
+	}
+	if ex.Valid {
+		p.ExcalidrawID = &ex.String
+	}
+	return &p, nil
+}
+
+// UpdatePort applies a partial update.
+func (s *Store) UpdatePort(projectID, id int64, u PortUpdate) (*Port, error) {
+	cur, err := s.GetPort(projectID, id)
+	if err != nil {
+		return nil, err
+	}
+	if u.TypeID != nil {
+		if _, err := s.GetCableType(*u.TypeID); err != nil {
+			if errors.Is(err, ErrNotFound) {
+				return nil, fmt.Errorf("%w: cable type %d not found", ErrInvalidInput, *u.TypeID)
+			}
+			return nil, err
+		}
+		cur.TypeID = *u.TypeID
+	}
+	if u.Label != nil {
+		v := strings.TrimSpace(*u.Label)
+		if v == "" {
+			cur.Label = nil
+		} else {
+			cur.Label = &v
+		}
+	}
+	if u.XOffset != nil {
+		cur.XOffset = *u.XOffset
+	}
+	if u.YOffset != nil {
+		cur.YOffset = *u.YOffset
+	}
+	var labelArg any
+	if cur.Label != nil {
+		labelArg = *cur.Label
+	}
+	if _, err := s.db.Exec(
+		`UPDATE ports
+		 SET type_id = ?, label = ?, x_offset = ?, y_offset = ?, updated_at = datetime('now')
+		 WHERE id = ? AND project_id = ?`,
+		cur.TypeID, labelArg, cur.XOffset, cur.YOffset, id, projectID,
+	); err != nil {
+		return nil, mapWriteErr(err)
+	}
+	return s.GetPort(projectID, id)
+}
+
+// DeletePort removes a port from a device. The schema's
+// ON DELETE SET NULL on cables.from_port_id / to_port_id collides with
+// the cable's CHECK ((from_port|from_device|from_io) = 1 non-null), so
+// we instead cascade-delete any cables that referenced the port on
+// either side — same effect from m's POV: the cable is gone, m can
+// re-draw if he still wants it.
+func (s *Store) DeletePort(projectID, id int64) error {
+	if _, err := s.GetPort(projectID, id); err != nil {
+		return err
+	}
+	tx, err := s.db.Begin()
+	if err != nil {
+		return err
+	}
+	defer tx.Rollback()
+	if _, err := tx.Exec(
+		`DELETE FROM cables WHERE project_id = ? AND (from_port_id = ? OR to_port_id = ?)`,
+		projectID, id, id,
+	); err != nil {
+		return err
+	}
+	if _, err := tx.Exec(
+		`DELETE FROM ports WHERE id = ? AND project_id = ?`, id, projectID,
+	); err != nil {
+		return err
+	}
+	return tx.Commit()
+}
+
+// ListPortsForDevice returns every port on one device, project-scoped.
+func (s *Store) ListPortsForDevice(projectID, deviceID int64) ([]Port, error) {
+	rows, err := s.db.Query(
+		`SELECT id, project_id, device_id, type_id, label, x_offset, y_offset,
+		        excalidraw_id, created_at, updated_at
+		 FROM ports WHERE project_id = ? AND device_id = ? ORDER BY id`,
+		projectID, deviceID,
+	)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	out := []Port{}
+	for rows.Next() {
+		var p Port
+		var label, ex sql.NullString
+		if err := rows.Scan(&p.ID, &p.ProjectID, &p.DeviceID, &p.TypeID, &label,
+			&p.XOffset, &p.YOffset, &ex, &p.CreatedAt, &p.UpdatedAt); err != nil {
+			return nil, err
+		}
+		if label.Valid {
+			v := label.String
+			p.Label = &v
+		}
+		if ex.Valid {
+			p.ExcalidrawID = &ex.String
+		}
+		out = append(out, p)
+	}
+	return out, rows.Err()
+}
+
+// ListPortsForProject returns every port in a project, ordered by
+// device_id + id so callers can group cheaply.
+func (s *Store) ListPortsForProject(projectID int64) ([]Port, error) {
+	rows, err := s.db.Query(
+		`SELECT id, project_id, device_id, type_id, label, x_offset, y_offset,
+		        excalidraw_id, created_at, updated_at
+		 FROM ports WHERE project_id = ? ORDER BY device_id, id`, projectID,
+	)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	out := []Port{}
+	for rows.Next() {
+		var p Port
+		var label, ex sql.NullString
+		if err := rows.Scan(&p.ID, &p.ProjectID, &p.DeviceID, &p.TypeID,
+			&label, &p.XOffset, &p.YOffset, &ex, &p.CreatedAt, &p.UpdatedAt); err != nil {
+			return nil, err
+		}
+		if label.Valid {
+			v := label.String
+			p.Label = &v
+		}
+		if ex.Valid {
+			p.ExcalidrawID = &ex.String
+		}
+		out = append(out, p)
+	}
+	return out, rows.Err()
+}
+
+// seedPortsFromType inserts the ports for a freshly-created device using
+// the type's `device_type_ports` profile. Port positions are computed by
+// laying out cable-type groups evenly along the configured edge of the
+// device, ordered by sort_order. Within a multi-count group the per-port
+// spacing is also even. Runs inside the same transaction as the device
+// insert so a failure rolls everything back.
+//
+// Layout strategy (v0):
+//   - All ports for a given type sit on the type's configured edge.
+//   - For each edge, compute total port count N (sum of count across
+//     entries on that edge) and distribute as t_i = (i + 1)/(N+1) along
+//     the edge length, so ports don't touch the corners.
+//   - For top/bottom: x_offset = w * t, y_offset = 0 (top) or h (bottom).
+//   - For left/right: x_offset = 0 (left) or w (right), y_offset = h * t.
+//   - Labels: '<prefix>' if count==1, '<prefix> N' (1-indexed) if count>1.
+//     Empty prefix → NULL label.
+func (s *Store) seedPortsFromType(tx *sql.Tx, projectID, deviceID, typeID int64, width, height float64) error {
+	rows, err := tx.Query(
+		`SELECT cable_type_id, label_prefix, count, edge, sort_order
+		 FROM device_type_ports
+		 WHERE device_type_id = ?
+		 ORDER BY edge, sort_order, id`, typeID,
+	)
+	if err != nil {
+		return err
+	}
+	type pendingPort struct {
+		cableTypeID int64
+		label       *string
+		xOff        float64
+		yOff        float64
+	}
+	// Group rows by edge first; emit per-port y-or-x slots inside each edge.
+	type groupRow struct {
+		cableTypeID int64
+		labelPrefix string
+		count       int
+	}
+	byEdge := map[string][]groupRow{}
+	for rows.Next() {
+		var g groupRow
+		var edge string
+		var sortOrder int
+		if err := rows.Scan(&g.cableTypeID, &g.labelPrefix, &g.count, &edge, &sortOrder); err != nil {
+			rows.Close()
+			return err
+		}
+		byEdge[edge] = append(byEdge[edge], g)
+	}
+	if err := rows.Close(); err != nil {
+		return err
+	}
+	if err := rows.Err(); err != nil {
+		return err
+	}
+
+	var pending []pendingPort
+	for _, edge := range []string{"top", "bottom", "left", "right"} {
+		groups := byEdge[edge]
+		if len(groups) == 0 {
+			continue
+		}
+		total := 0
+		for _, g := range groups {
+			total += g.count
+		}
+		if total == 0 {
+			continue
+		}
+		// Emit ports in group + within-group order.
+		idx := 0
+		for _, g := range groups {
+			for k := 0; k < g.count; k++ {
+				t := float64(idx+1) / float64(total+1)
+				var xOff, yOff float64
+				switch edge {
+				case "top":
+					xOff, yOff = width*t, 0
+				case "bottom":
+					xOff, yOff = width*t, height
+				case "left":
+					xOff, yOff = 0, height*t
+				case "right":
+					xOff, yOff = width, height*t
+				}
+				var labelPtr *string
+				if g.labelPrefix != "" {
+					var lbl string
+					if g.count == 1 {
+						lbl = g.labelPrefix
+					} else {
+						lbl = g.labelPrefix + " " + itoa(k+1)
+					}
+					labelPtr = &lbl
+				}
+				pending = append(pending, pendingPort{
+					cableTypeID: g.cableTypeID, label: labelPtr,
+					xOff: xOff, yOff: yOff,
+				})
+				idx++
+			}
+		}
+	}
+
+	for _, p := range pending {
+		var labelArg any
+		if p.label != nil {
+			labelArg = *p.label
+		}
+		if _, err := tx.Exec(
+			`INSERT INTO ports (project_id, device_id, type_id, label, x_offset, y_offset)
+			 VALUES (?, ?, ?, ?, ?, ?)`,
+			projectID, deviceID, p.cableTypeID, labelArg, p.xOff, p.yOff,
+		); err != nil {
+			return mapWriteErr(err)
+		}
+	}
+	return nil
+}
+
+// itoa is a tiny non-allocating int-to-string for port labels.
+func itoa(i int) string {
+	if i == 0 {
+		return "0"
+	}
+	buf := [20]byte{}
+	pos := len(buf)
+	neg := i < 0
+	if neg {
+		i = -i
+	}
+	for i > 0 {
+		pos--
+		buf[pos] = byte('0' + i%10)
+		i /= 10
+	}
+	if neg {
+		pos--
+		buf[pos] = '-'
+	}
+	return string(buf[pos:])
+}

internal/db/setup_templates.go

@@ -0,0 +1,367 @@
+package db
+
+import (
+	"database/sql"
+	"errors"
+	"fmt"
+	"strings"
+)
+
+// ListSetupTemplates returns every template with its devices +
+// requirements hydrated.
+func (s *Store) ListSetupTemplates() ([]SetupTemplate, error) {
+	rows, err := s.db.Query(
+		`SELECT id, name, description, built_in, created_at, updated_at
+		 FROM setup_templates ORDER BY id`,
+	)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	out := []SetupTemplate{}
+	for rows.Next() {
+		var t SetupTemplate
+		var built int
+		if err := rows.Scan(&t.ID, &t.Name, &t.Description, &built,
+			&t.CreatedAt, &t.UpdatedAt); err != nil {
+			return nil, err
+		}
+		t.BuiltIn = built != 0
+		out = append(out, t)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	for i := range out {
+		devs, err := s.listTemplateDevices(out[i].ID)
+		if err != nil {
+			return nil, err
+		}
+		out[i].Devices = devs
+		reqs, err := s.listTemplateRequirements(out[i].ID)
+		if err != nil {
+			return nil, err
+		}
+		out[i].Requirements = reqs
+	}
+	return out, nil
+}
+
+// GetSetupTemplate is a one-template variant of List.
+func (s *Store) GetSetupTemplate(id int64) (*SetupTemplate, error) {
+	var t SetupTemplate
+	var built int
+	err := s.db.QueryRow(
+		`SELECT id, name, description, built_in, created_at, updated_at
+		 FROM setup_templates WHERE id = ?`, id,
+	).Scan(&t.ID, &t.Name, &t.Description, &built, &t.CreatedAt, &t.UpdatedAt)
+	if errors.Is(err, sql.ErrNoRows) {
+		return nil, ErrNotFound
+	}
+	if err != nil {
+		return nil, err
+	}
+	t.BuiltIn = built != 0
+	t.Devices, err = s.listTemplateDevices(t.ID)
+	if err != nil {
+		return nil, err
+	}
+	t.Requirements, err = s.listTemplateRequirements(t.ID)
+	if err != nil {
+		return nil, err
+	}
+	return &t, nil
+}
+
+func (s *Store) listTemplateDevices(templateID int64) ([]SetupTemplateDevice, error) {
+	rows, err := s.db.Query(
+		`SELECT id, template_id, device_type_id, suggested_name, sort_order
+		 FROM setup_template_devices WHERE template_id = ? ORDER BY sort_order, id`,
+		templateID,
+	)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	out := []SetupTemplateDevice{}
+	for rows.Next() {
+		var d SetupTemplateDevice
+		var sn sql.NullString
+		if err := rows.Scan(&d.ID, &d.TemplateID, &d.DeviceTypeID, &sn, &d.SortOrder); err != nil {
+			return nil, err
+		}
+		if sn.Valid {
+			v := sn.String
+			d.SuggestedName = &v
+		}
+		out = append(out, d)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	// Hydrate the device_type for the UI's optgroup labels.
+	for i := range out {
+		dt, err := s.GetDeviceType(out[i].DeviceTypeID)
+		if err == nil {
+			out[i].DeviceType = dt
+		}
+	}
+	return out, nil
+}
+
+func (s *Store) listTemplateRequirements(templateID int64) ([]SetupTemplateRequirement, error) {
+	rows, err := s.db.Query(
+		`SELECT id, template_id, from_template_device_id, to_template_device_id,
+		        preferred_cable_type_id, must_connect
+		 FROM setup_template_requirements WHERE template_id = ? ORDER BY id`,
+		templateID,
+	)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	out := []SetupTemplateRequirement{}
+	for rows.Next() {
+		var r SetupTemplateRequirement
+		var pct sql.NullInt64
+		var must int
+		if err := rows.Scan(&r.ID, &r.TemplateID, &r.FromTemplateDeviceID, &r.ToTemplateDeviceID,
+			&pct, &must); err != nil {
+			return nil, err
+		}
+		if pct.Valid {
+			v := pct.Int64
+			r.PreferredCableTypeID = &v
+		}
+		r.MustConnect = must != 0
+		out = append(out, r)
+	}
+	return out, rows.Err()
+}
+
+// ApplyTemplateOptions controls per-device name overrides + opt-outs.
+type ApplyTemplateOptions struct {
+	NameOverrides map[int64]string // template_device_id → custom name
+	SkipDevices   map[int64]bool   // template_device_id → skip
+	// Layout: where to place the first device in the cluster on the canvas.
+	OriginX, OriginY float64
+}
+
+// ApplyTemplate seeds devices + requirements from the template into
+// projectID in a single transaction. Name collisions skip the device
+// (recorded in skipped_devices); requirements whose endpoints both fail
+// to land are also skipped.
+func (s *Store) ApplyTemplate(projectID, templateID int64, opts ApplyTemplateOptions) (*ApplyTemplateResult, error) {
+	tmpl, err := s.GetSetupTemplate(templateID)
+	if err != nil {
+		return nil, err
+	}
+	if _, err := s.GetProject(projectID); err != nil {
+		return nil, err
+	}
+
+	out := &ApplyTemplateResult{
+		DevicesAdded:        []Device{},
+		RequirementsAdded:   []ConnectionRequirement{},
+		SkippedDevices:      []SkippedTemplateDevice{},
+		RequirementsSkipped: []SkippedTemplateReq{},
+	}
+
+	if opts.OriginX == 0 && opts.OriginY == 0 {
+		opts.OriginX, opts.OriginY = 200, 200
+	}
+
+	// Pull existing device names in the project so we can pre-check
+	// collisions without aborting the whole transaction.
+	existing, err := s.ListDevices(projectID, nil)
+	if err != nil {
+		return nil, err
+	}
+	nameTaken := map[string]bool{}
+	for _, d := range existing {
+		nameTaken[d.Name] = true
+	}
+
+	tx, err := s.db.Begin()
+	if err != nil {
+		return nil, err
+	}
+	defer tx.Rollback()
+
+	// Map: template_device_id → newly-created device_id (or 0 if skipped).
+	tmplToDevice := map[int64]int64{}
+
+	for i, td := range tmpl.Devices {
+		if opts.SkipDevices[td.ID] {
+			out.SkippedDevices = append(out.SkippedDevices, SkippedTemplateDevice{
+				TemplateDeviceID: td.ID, Reason: "skip requested",
+			})
+			tmplToDevice[td.ID] = 0
+			continue
+		}
+		name := opts.NameOverrides[td.ID]
+		if name == "" && td.SuggestedName != nil {
+			name = *td.SuggestedName
+		}
+		if name == "" {
+			name = fmt.Sprintf("Device %d", td.ID)
+		}
+		name = strings.TrimSpace(name)
+		if nameTaken[name] {
+			out.SkippedDevices = append(out.SkippedDevices, SkippedTemplateDevice{
+				TemplateDeviceID: td.ID,
+				Reason:           fmt.Sprintf("name %q already used in project", name),
+			})
+			tmplToDevice[td.ID] = 0
+			continue
+		}
+		// Lay out devices in a horizontal row near the origin, 150 px apart.
+		x := opts.OriginX + float64(i)*150
+		y := opts.OriginY
+		// Use createDeviceTx so the port-seeding share the same transaction.
+		d, err := s.createDeviceTx(tx, projectID, DeviceCreate{
+			Name:    name,
+			TypeID:  &td.DeviceTypeID,
+			X:       x,
+			Y:       y,
+			Width:   100,
+			Height:  35,
+		})
+		if err != nil {
+			return nil, fmt.Errorf("seed %s: %w", name, err)
+		}
+		nameTaken[name] = true
+		tmplToDevice[td.ID] = d.ID
+		out.DevicesAdded = append(out.DevicesAdded, *d)
+	}
+
+	for _, tr := range tmpl.Requirements {
+		fromID := tmplToDevice[tr.FromTemplateDeviceID]
+		toID := tmplToDevice[tr.ToTemplateDeviceID]
+		if fromID == 0 || toID == 0 {
+			out.RequirementsSkipped = append(out.RequirementsSkipped, SkippedTemplateReq{
+				TemplateRequirementID: tr.ID,
+				Reason:                "one or both endpoint devices were skipped",
+			})
+			continue
+		}
+		// Normalise pair_lo/pair_hi, mirror what CreateConnectionRequirement does.
+		lo, hi := fromID, toID
+		if lo > hi {
+			lo, hi = hi, lo
+		}
+		must := 0
+		if tr.MustConnect {
+			must = 1
+		}
+		var ctArg any
+		if tr.PreferredCableTypeID != nil {
+			ctArg = *tr.PreferredCableTypeID
+		}
+		res, err := tx.Exec(
+			`INSERT INTO connection_requirements
+			   (project_id, from_device_id, to_device_id, preferred_cable_type_id,
+			    must_connect, notes, pair_lo, pair_hi)
+			 VALUES (?, ?, ?, ?, ?, '', ?, ?)`,
+			projectID, fromID, toID, ctArg, must, lo, hi,
+		)
+		if err != nil {
+			// A UNIQUE collision (project already has the same requirement)
+			// is non-fatal — record as skipped, continue.
+			if strings.Contains(err.Error(), "UNIQUE constraint failed") {
+				out.RequirementsSkipped = append(out.RequirementsSkipped, SkippedTemplateReq{
+					TemplateRequirementID: tr.ID,
+					Reason:                "requirement already exists in project",
+				})
+				continue
+			}
+			return nil, err
+		}
+		rid, _ := res.LastInsertId()
+		out.RequirementsAdded = append(out.RequirementsAdded, ConnectionRequirement{
+			ID:                   rid,
+			ProjectID:            projectID,
+			FromDeviceID:         fromID,
+			ToDeviceID:           toID,
+			PreferredCableTypeID: tr.PreferredCableTypeID,
+			MustConnect:          tr.MustConnect,
+		})
+	}
+
+	if err := tx.Commit(); err != nil {
+		return nil, err
+	}
+	return out, nil
+}
+
+// createDeviceTx is a tx-aware variant of CreateDevice used by
+// ApplyTemplate so seeding the template's devices + their ports stays
+// inside one atomic apply.
+//
+// Validation is intentionally lighter than CreateDevice: callers (only
+// ApplyTemplate today) hold a tx on the single SQLite connection, so
+// any "validate by reading from s.db" call would deadlock. The template's
+// device_type_id + frame_id come from already-validated template rows,
+// and SQLite FK constraints catch any genuine corruption on INSERT
+// (mapped to ErrInvalidInput by mapWriteErr).
+func (s *Store) createDeviceTx(tx *sql.Tx, projectID int64, d DeviceCreate) (*Device, error) {
+	name := strings.TrimSpace(d.Name)
+	if name == "" {
+		return nil, fmt.Errorf("%w: name is required", ErrInvalidInput)
+	}
+	if d.Width <= 0 || d.Height <= 0 {
+		return nil, fmt.Errorf("%w: width and height must be positive", ErrInvalidInput)
+	}
+	color := strings.TrimSpace(d.Color)
+	if color == "" {
+		color = "#1e1e1e"
+	}
+	res, err := tx.Exec(
+		`INSERT INTO devices (project_id, frame_id, type_id, name, color, x, y, width, height)
+		 VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?)`,
+		projectID, nullableInt64(d.FrameID), nullableInt64(d.TypeID),
+		name, color, d.X, d.Y, d.Width, d.Height,
+	)
+	if err != nil {
+		return nil, mapWriteErr(err)
+	}
+	deviceID, _ := res.LastInsertId()
+	if d.TypeID != nil {
+		if err := s.seedPortsFromType(tx, projectID, deviceID, *d.TypeID, d.Width, d.Height); err != nil {
+			return nil, err
+		}
+	}
+	// Read back via the public store path is fine — the row exists in
+	// the in-flight tx and SQLite sees its own writes within the tx.
+	// Use a sub-helper that takes the tx executor for clean isolation.
+	return s.readDeviceTx(tx, projectID, deviceID)
+}
+
+func (s *Store) readDeviceTx(ex execer, projectID, id int64) (*Device, error) {
+	var d Device
+	var frame, typeID sql.NullInt64
+	var ex2 sql.NullString
+	err := ex.QueryRow(
+		`SELECT id, project_id, frame_id, type_id, name, color, x, y, width, height, excalidraw_id, created_at, updated_at
+		 FROM devices WHERE id = ? AND project_id = ?`, id, projectID,
+	).Scan(&d.ID, &d.ProjectID, &frame, &typeID, &d.Name, &d.Color, &d.X, &d.Y, &d.Width, &d.Height,
+		&ex2, &d.CreatedAt, &d.UpdatedAt)
+	if errors.Is(err, sql.ErrNoRows) {
+		return nil, ErrNotFound
+	}
+	if err != nil {
+		return nil, err
+	}
+	if frame.Valid {
+		v := frame.Int64
+		d.FrameID = &v
+	}
+	if typeID.Valid {
+		v := typeID.Int64
+		d.TypeID = &v
+	}
+	if ex2.Valid {
+		d.ExcalidrawID = &ex2.String
+	}
+	return &d, nil
+}

internal/db/solver.go

@@ -0,0 +1,509 @@
+package db
+
+import (
+	"database/sql"
+	"fmt"
+	"sort"
+)
+
+// Solve runs the v0 algorithm (design v4.1 §5b.2) against the project.
+// If preview is true, no DB writes happen — the function returns the
+// diff it WOULD apply. If preview is false, the diff is applied in a
+// single transaction.
+//
+// Algorithm:
+//   1. Read all auto cables, manual cables, ports, requirements.
+//   2. Reserve ports used by manual cables (auto=0) so the solver
+//      doesn't reuse them.
+//   3. For each requirement (must_connect DESC, id ASC):
+//        - Resolve cable type: preferred, or T = port-types(from) ∩
+//          port-types(to). |T|==1 → that. |T|>1 → unsatisfied (ambiguous).
+//          |T|==0 → unsatisfied (no compat type).
+//        - Find lowest-id free port on each side. None → unsatisfied
+//          (no free port). Reserve both.
+//        - Stage an "add cable {from_port, to_port, type, auto=1}".
+//   4. Endpoint-pair bundle: any pair of device endpoints with ≥ 2
+//      staged cables becomes an auto bundle.
+//   5. Diff against existing auto cables/bundles: removed = existing
+//      auto rows not in the staged set; kept = those that match by
+//      (from_port, to_port, type); add = remaining staged rows.
+func (s *Store) Solve(projectID int64, preview bool) (*SolveResult, error) {
+	res := &SolveResult{
+		CablesAdded:    []Cable{},
+		CablesKept:     []int64{},
+		CablesRemoved:  []int64{},
+		BundlesAdded:   []Bundle{},
+		BundlesRemoved: []int64{},
+		Unsatisfied:    []UnsatisfiedReq{},
+		Warnings:       []string{},
+	}
+
+	if _, err := s.GetProject(projectID); err != nil {
+		return nil, err
+	}
+	devices, err := s.ListDevices(projectID, nil)
+	if err != nil {
+		return nil, err
+	}
+	ports, err := s.ListPortsForProject(projectID)
+	if err != nil {
+		return nil, err
+	}
+	cables, err := s.ListCables(projectID)
+	if err != nil {
+		return nil, err
+	}
+	reqs, err := s.ListConnectionRequirements(projectID)
+	if err != nil {
+		return nil, err
+	}
+	bundles, err := s.ListBundles(projectID)
+	if err != nil {
+		return nil, err
+	}
+
+	// Index ports by (device_id, type_id), sorted by id (deterministic).
+	portsByDevice := map[int64][]Port{}
+	for _, p := range ports {
+		portsByDevice[p.DeviceID] = append(portsByDevice[p.DeviceID], p)
+	}
+	for did := range portsByDevice {
+		sort.SliceStable(portsByDevice[did], func(i, j int) bool {
+			return portsByDevice[did][i].ID < portsByDevice[did][j].ID
+		})
+	}
+	deviceByID := map[int64]Device{}
+	for _, d := range devices {
+		deviceByID[d.ID] = d
+	}
+
+	// Reserve ports used by manual cables.
+	usedPorts := map[int64]bool{}
+	autoCablesByID := map[int64]Cable{}
+	for _, c := range cables {
+		if c.Auto {
+			autoCablesByID[c.ID] = c
+			continue
+		}
+		if c.FromPortID != nil {
+			usedPorts[*c.FromPortID] = true
+		}
+		if c.ToPortID != nil {
+			usedPorts[*c.ToPortID] = true
+		}
+	}
+
+	// Sort requirements: must_connect DESC, id ASC.
+	rs := append([]ConnectionRequirement{}, reqs...)
+	sort.SliceStable(rs, func(i, j int) bool {
+		if rs[i].MustConnect != rs[j].MustConnect {
+			return rs[i].MustConnect
+		}
+		return rs[i].ID < rs[j].ID
+	})
+
+	type staged struct {
+		typeID       int64
+		fromPortID   int64
+		toPortID     int64
+		fromDeviceID int64
+		toDeviceID   int64
+	}
+	var staging []staged
+
+	for _, r := range rs {
+		_, fromOK := deviceByID[r.FromDeviceID]
+		_, toOK := deviceByID[r.ToDeviceID]
+		if !fromOK || !toOK {
+			// Shouldn't happen (FK CASCADE removes the row when a device
+			// goes), but be defensive.
+			continue
+		}
+
+		// Resolve cable type.
+		var typeID int64
+		if r.PreferredCableTypeID != nil {
+			typeID = *r.PreferredCableTypeID
+		} else {
+			fromTypes := map[int64]bool{}
+			for _, p := range portsByDevice[r.FromDeviceID] {
+				fromTypes[p.TypeID] = true
+			}
+			candidates := []int64{}
+			for _, p := range portsByDevice[r.ToDeviceID] {
+				if fromTypes[p.TypeID] {
+					// Add unique.
+					already := false
+					for _, c := range candidates {
+						if c == p.TypeID {
+							already = true
+							break
+						}
+					}
+					if !already {
+						candidates = append(candidates, p.TypeID)
+					}
+				}
+			}
+			if len(candidates) == 0 {
+				if r.MustConnect {
+					res.Unsatisfied = append(res.Unsatisfied, UnsatisfiedReq{
+						RequirementID: r.ID,
+						Reason:        "no compatible cable type — devices share no port-type",
+					})
+				}
+				continue
+			}
+			if len(candidates) > 1 {
+				if r.MustConnect {
+					res.Unsatisfied = append(res.Unsatisfied, UnsatisfiedReq{
+						RequirementID: r.ID,
+						Reason:        "ambiguous cable type — specify preferred_cable_type_id",
+					})
+				}
+				continue
+			}
+			typeID = candidates[0]
+		}
+
+		// Pick lowest-id free port of `typeID` on each side.
+		pickFree := func(deviceID, t int64) *int64 {
+			for _, p := range portsByDevice[deviceID] {
+				if p.TypeID != t {
+					continue
+				}
+				if usedPorts[p.ID] {
+					continue
+				}
+				return &p.ID
+			}
+			return nil
+		}
+		fromPort := pickFree(r.FromDeviceID, typeID)
+		toPort := pickFree(r.ToDeviceID, typeID)
+		if fromPort == nil || toPort == nil {
+			if r.MustConnect {
+				side := ""
+				if fromPort == nil && toPort == nil {
+					side = ""
+				} else if fromPort == nil {
+					side = "from"
+				} else {
+					side = "to"
+				}
+				typeName := ""
+				if ct, err := s.GetCableType(typeID); err == nil {
+					typeName = ct.Name
+				}
+				res.Unsatisfied = append(res.Unsatisfied, UnsatisfiedReq{
+					RequirementID: r.ID,
+					Reason:        fmt.Sprintf("no free %s port", typeName),
+					WhichSide:     side,
+					CableType:     typeName,
+				})
+			}
+			continue
+		}
+		usedPorts[*fromPort] = true
+		usedPorts[*toPort] = true
+		staging = append(staging, staged{
+			typeID: typeID, fromPortID: *fromPort, toPortID: *toPort,
+			fromDeviceID: r.FromDeviceID, toDeviceID: r.ToDeviceID,
+		})
+	}
+
+	// Match staged → existing auto cables by (typeID, fromPortID, toPortID)
+	// or its reverse. Anything matched is "kept"; the rest of auto cables
+	// is "removed". Unmatched staged entries become "added".
+	type sigKey struct{ typeID, a, b int64 }
+	matched := map[int64]bool{} // existing auto cable IDs that match
+	sigToAuto := map[sigKey]int64{}
+	for id, c := range autoCablesByID {
+		if c.FromPortID == nil || c.ToPortID == nil {
+			continue
+		}
+		a, b := *c.FromPortID, *c.ToPortID
+		if a > b {
+			a, b = b, a
+		}
+		sigToAuto[sigKey{c.TypeID, a, b}] = id
+	}
+	var toAdd []staged
+	for _, st := range staging {
+		a, b := st.fromPortID, st.toPortID
+		if a > b {
+			a, b = b, a
+		}
+		if existingID, ok := sigToAuto[sigKey{st.typeID, a, b}]; ok {
+			matched[existingID] = true
+			res.CablesKept = append(res.CablesKept, existingID)
+			continue
+		}
+		toAdd = append(toAdd, st)
+	}
+	for id := range autoCablesByID {
+		if !matched[id] {
+			res.CablesRemoved = append(res.CablesRemoved, id)
+		}
+	}
+	sort.Slice(res.CablesKept, func(i, j int) bool { return res.CablesKept[i] < res.CablesKept[j] })
+	sort.Slice(res.CablesRemoved, func(i, j int) bool { return res.CablesRemoved[i] < res.CablesRemoved[j] })
+
+	// Endpoint-pair bundling for the final set of auto cables (kept + added).
+	// Group by unordered (deviceA, deviceB). Build the map of port_id → device_id
+	// for fast lookup.
+	portToDevice := map[int64]int64{}
+	for _, p := range ports {
+		portToDevice[p.ID] = p.DeviceID
+	}
+	type pairKey struct{ a, b int64 }
+	pairGroup := map[pairKey][]string{} // staged-or-kept tags (we just count)
+	pairOrder := []pairKey{}            // first-seen order
+
+	// We'll need the final list of cables-after-apply (with their IDs) to
+	// build bundles. For preview, kept IDs are real, added IDs are zero;
+	// for apply, we'll re-bundle after inserts.
+
+	if preview {
+		// In preview mode, "kept" IDs are real cables; "added" are
+		// staged. We still compute bundles_added so the UI can show
+		// which cable groups will be bundled. Bundles_added carry
+		// `CableIDs: []` for the staged entries because they don't
+		// have IDs yet — the UI maps by position. cables_kept that
+		// belong to a bundle group also list their existing ids.
+		// In short, slot every staged cable into the same pair bucket
+		// + the kept cables.
+		for _, st := range staging {
+			da, db := st.fromDeviceID, st.toDeviceID
+			if da > db {
+				da, db = db, da
+			}
+			pk := pairKey{da, db}
+			if _, ok := pairGroup[pk]; !ok {
+				pairOrder = append(pairOrder, pk)
+			}
+			pairGroup[pk] = append(pairGroup[pk], "")
+		}
+		// Materialise preview-shape Cable structs for the added rows.
+		for _, st := range toAdd {
+			c := Cable{
+				ProjectID:  projectID,
+				TypeID:     st.typeID,
+				FromPortID: ptr(st.fromPortID),
+				ToPortID:   ptr(st.toPortID),
+				Auto:       true,
+			}
+			res.CablesAdded = append(res.CablesAdded, c)
+		}
+		for _, pk := range pairOrder {
+			if len(pairGroup[pk]) < 2 {
+				continue
+			}
+			a := deviceByID[pk.a].Name
+			b := deviceByID[pk.b].Name
+			res.BundlesAdded = append(res.BundlesAdded, Bundle{
+				ProjectID: projectID,
+				Name:      a + " ↔ " + b,
+				Auto:      true,
+				CableIDs:  nil, // post-apply only
+			})
+		}
+		// Existing auto bundles all "would be removed" since we rebuild
+		// from scratch each solve (slice-6 v0 is wholesale-replace).
+		for _, b := range bundles {
+			if b.Auto {
+				res.BundlesRemoved = append(res.BundlesRemoved, b.ID)
+			}
+		}
+		return res, nil
+	}
+
+	// Apply mode: open a transaction, delete removed auto cables + auto
+	// bundles, insert added cables, re-bundle by endpoint pair.
+	tx, err := s.db.Begin()
+	if err != nil {
+		return nil, err
+	}
+	defer tx.Rollback()
+
+	// Delete obsolete auto bundles (we'll rebuild).
+	if _, err := tx.Exec(
+		`DELETE FROM bundles WHERE project_id = ? AND auto = 1`, projectID,
+	); err != nil {
+		return nil, err
+	}
+	for _, b := range bundles {
+		if b.Auto {
+			res.BundlesRemoved = append(res.BundlesRemoved, b.ID)
+		}
+	}
+
+	// Delete removed auto cables.
+	for _, id := range res.CablesRemoved {
+		if _, err := tx.Exec(
+			`DELETE FROM cables WHERE id = ? AND project_id = ?`, id, projectID,
+		); err != nil {
+			return nil, err
+		}
+	}
+
+	// Insert added cables. Track new ids by their staged signature for
+	// bundle wiring.
+	type addedRow struct {
+		id           int64
+		staged       staged
+	}
+	addedRows := []addedRow{}
+	for _, st := range toAdd {
+		c, err := s.createCable(tx, projectID, CableCreate{
+			TypeID: st.typeID,
+			From:   CableEndpoint{PortID: &st.fromPortID},
+			To:     CableEndpoint{PortID: &st.toPortID},
+			Auto:   true,
+		})
+		if err != nil {
+			return nil, err
+		}
+		res.CablesAdded = append(res.CablesAdded, *c)
+		addedRows = append(addedRows, addedRow{id: c.ID, staged: st})
+	}
+
+	// Re-bundle: all auto cables (kept + added) grouped by endpoint pair.
+	// First, collect cable IDs per (deviceA, deviceB) — both kept (from
+	// matched map) and added.
+	groups := map[pairKey][]int64{}
+	order := []pairKey{}
+	addToGroup := func(da, db, cid int64) {
+		if da > db {
+			da, db = db, da
+		}
+		pk := pairKey{da, db}
+		if _, ok := groups[pk]; !ok {
+			order = append(order, pk)
+		}
+		groups[pk] = append(groups[pk], cid)
+	}
+	for id, c := range autoCablesByID {
+		if !matched[id] {
+			continue
+		}
+		if c.FromPortID == nil || c.ToPortID == nil {
+			continue
+		}
+		da := portToDevice[*c.FromPortID]
+		db := portToDevice[*c.ToPortID]
+		if da == 0 || db == 0 {
+			continue
+		}
+		addToGroup(da, db, id)
+	}
+	for _, ar := range addedRows {
+		addToGroup(ar.staged.fromDeviceID, ar.staged.toDeviceID, ar.id)
+	}
+
+	for _, pk := range order {
+		ids := groups[pk]
+		if len(ids) < 2 {
+			continue
+		}
+		a := deviceByID[pk.a].Name
+		b := deviceByID[pk.b].Name
+		bundle, err := s.createBundle(tx, projectID, BundleCreate{
+			Name:     a + " ↔ " + b,
+			CableIDs: ids,
+			Auto:     true,
+		}, false)
+		if err != nil {
+			return nil, err
+		}
+		res.BundlesAdded = append(res.BundlesAdded, *bundle)
+	}
+
+	if err := tx.Commit(); err != nil {
+		return nil, err
+	}
+	return res, nil
+}
+
+func ptr[T any](v T) *T { return &v }
+
+// PortsAndResolve adds a port to a device + re-runs Solve in one tx.
+// Used by the inspector's "+ Add <type> port and re-solve" quick-fix.
+type PortsAndResolveResult struct {
+	Port  Port         `json:"port"`
+	Solve *SolveResult `json:"solve"`
+}
+
+func (s *Store) PortsAndResolve(projectID, deviceID int64, typeID int64, label string, xOff, yOff float64) (*PortsAndResolveResult, error) {
+	d, err := s.GetDevice(projectID, deviceID)
+	if err != nil {
+		return nil, err
+	}
+	if _, err := s.GetCableType(typeID); err != nil {
+		if err == sql.ErrNoRows {
+			return nil, fmt.Errorf("%w: cable type %d not found", ErrInvalidInput, typeID)
+		}
+	}
+	tx, err := s.db.Begin()
+	if err != nil {
+		return nil, err
+	}
+	defer tx.Rollback()
+	// Default the new port to the bottom edge at the right-most existing offset.
+	if xOff == 0 && yOff == 0 {
+		xOff = d.Width / 2
+		yOff = d.Height
+	}
+	var labelArg any
+	if label != "" {
+		labelArg = label
+	}
+	res, err := tx.Exec(
+		`INSERT INTO ports (project_id, device_id, type_id, label, x_offset, y_offset)
+		 VALUES (?, ?, ?, ?, ?, ?)`,
+		projectID, deviceID, typeID, labelArg, xOff, yOff,
+	)
+	if err != nil {
+		return nil, mapWriteErr(err)
+	}
+	portID, _ := res.LastInsertId()
+	if err := tx.Commit(); err != nil {
+		return nil, err
+	}
+	// Now re-solve outside the tx — Solve manages its own tx for the
+	// apply path. This is a slight relaxation of "single round-trip" — if
+	// the solver run fails the port stays, but that's fine; the port is
+	// what m wanted regardless.
+	solveRes, err := s.Solve(projectID, false)
+	if err != nil {
+		return nil, err
+	}
+	// Re-fetch the port row to return its full shape.
+	port, err := s.getPortByID(portID)
+	if err != nil {
+		return nil, err
+	}
+	return &PortsAndResolveResult{Port: *port, Solve: solveRes}, nil
+}
+
+func (s *Store) getPortByID(id int64) (*Port, error) {
+	var p Port
+	var label, ex sql.NullString
+	err := s.db.QueryRow(
+		`SELECT id, project_id, device_id, type_id, label, x_offset, y_offset,
+		        excalidraw_id, created_at, updated_at
+		 FROM ports WHERE id = ?`, id,
+	).Scan(&p.ID, &p.ProjectID, &p.DeviceID, &p.TypeID, &label,
+		&p.XOffset, &p.YOffset, &ex, &p.CreatedAt, &p.UpdatedAt)
+	if err != nil {
+		return nil, err
+	}
+	if label.Valid {
+		v := label.String
+		p.Label = &v
+	}
+	if ex.Valid {
+		p.ExcalidrawID = &ex.String
+	}
+	return &p, nil
+}

internal/db/solver_test.go

@@ -0,0 +1,259 @@
+package db
+
+import (
+	"testing"
+)
+
+// builtInTypeID returns the id of the named built-in device type.
+func builtInTypeID(t *testing.T, s *Store, name string) int64 {
+	t.Helper()
+	all, _ := s.ListBuiltInDeviceTypes()
+	for _, dt := range all {
+		if dt.Name == name {
+			return dt.ID
+		}
+	}
+	t.Fatalf("built-in %q not found", name)
+	return 0
+}
+
+// ------------------------------------------------------ basic solver wins
+
+func TestSolve_BasicNAStoSwitch(t *testing.T) {
+	s := newTestStore(t)
+	p, _ := s.CreateProject("LOFT", "", "")
+	nasT := builtInTypeID(t, s, "NAS")
+	swT := builtInTypeID(t, s, "Switch")
+	nas, _ := s.CreateDevice(p.ID, DeviceCreate{Name: "NAS", TypeID: &nasT, X: 0, Y: 0, Width: 100, Height: 35})
+	sw, _ := s.CreateDevice(p.ID, DeviceCreate{Name: "Switch", TypeID: &swT, X: 200, Y: 0, Width: 100, Height: 35})
+	rj45 := int64(5)
+	_, _ = s.CreateConnectionRequirement(p.ID, ConnectionRequirementCreate{
+		FromDeviceID: nas.ID, ToDeviceID: sw.ID, PreferredCableTypeID: &rj45,
+	})
+	res, err := s.Solve(p.ID, false)
+	if err != nil {
+		t.Fatalf("solve: %v", err)
+	}
+	if len(res.CablesAdded) != 1 {
+		t.Fatalf("cables_added len = %d, want 1", len(res.CablesAdded))
+	}
+	if res.CablesAdded[0].TypeID != rj45 {
+		t.Errorf("cable type = %d, want %d (RJ45)", res.CablesAdded[0].TypeID, rj45)
+	}
+	if !res.CablesAdded[0].Auto {
+		t.Errorf("cable.auto should be true")
+	}
+	if len(res.Unsatisfied) != 0 {
+		t.Errorf("unsatisfied should be empty; got %+v", res.Unsatisfied)
+	}
+}
+
+func TestSolve_AmbiguousType_RequirementUnsatisfied(t *testing.T) {
+	s := newTestStore(t)
+	p, _ := s.CreateProject("LOFT", "", "")
+	// Both PCs have Power + USB + HDMI + RJ45 → multiple types match.
+	pcT := builtInTypeID(t, s, "PC")
+	a, _ := s.CreateDevice(p.ID, DeviceCreate{Name: "A", TypeID: &pcT, X: 0, Y: 0, Width: 100, Height: 35})
+	b, _ := s.CreateDevice(p.ID, DeviceCreate{Name: "B", TypeID: &pcT, X: 200, Y: 0, Width: 100, Height: 35})
+	_, _ = s.CreateConnectionRequirement(p.ID, ConnectionRequirementCreate{
+		FromDeviceID: a.ID, ToDeviceID: b.ID, // no PreferredCableTypeID
+	})
+	res, _ := s.Solve(p.ID, true)
+	if len(res.CablesAdded) != 0 {
+		t.Errorf("ambiguous: should not add cables, got %d", len(res.CablesAdded))
+	}
+	if len(res.Unsatisfied) != 1 || res.Unsatisfied[0].Reason == "" {
+		t.Errorf("expected 1 unsatisfied req with non-empty reason; got %+v", res.Unsatisfied)
+	}
+}
+
+func TestSolve_NoFreePort_RequirementUnsatisfied(t *testing.T) {
+	s := newTestStore(t)
+	p, _ := s.CreateProject("LOFT", "", "")
+	// Mouse only has 1 USB port. Two USB requirements against it should
+	// leave one unsatisfied.
+	mouseT := builtInTypeID(t, s, "Mouse")
+	pcT := builtInTypeID(t, s, "PC")
+	mouse, _ := s.CreateDevice(p.ID, DeviceCreate{Name: "Mouse", TypeID: &mouseT, X: 0, Y: 0, Width: 100, Height: 35})
+	pc1, _ := s.CreateDevice(p.ID, DeviceCreate{Name: "PC1", TypeID: &pcT, X: 200, Y: 0, Width: 100, Height: 35})
+	pc2, _ := s.CreateDevice(p.ID, DeviceCreate{Name: "PC2", TypeID: &pcT, X: 400, Y: 0, Width: 100, Height: 35})
+	usb := int64(2)
+	_, _ = s.CreateConnectionRequirement(p.ID, ConnectionRequirementCreate{
+		FromDeviceID: mouse.ID, ToDeviceID: pc1.ID, PreferredCableTypeID: &usb,
+	})
+	_, _ = s.CreateConnectionRequirement(p.ID, ConnectionRequirementCreate{
+		FromDeviceID: mouse.ID, ToDeviceID: pc2.ID, PreferredCableTypeID: &usb,
+	})
+	res, _ := s.Solve(p.ID, true)
+	if len(res.CablesAdded) != 1 {
+		t.Errorf("expected 1 cable to land (one mouse USB), got %d", len(res.CablesAdded))
+	}
+	if len(res.Unsatisfied) != 1 {
+		t.Errorf("expected 1 unsatisfied; got %d (%+v)", len(res.Unsatisfied), res.Unsatisfied)
+	}
+}
+
+// ----------------------------------------------- preview vs apply semantics
+
+func TestSolve_PreviewDoesNotWrite(t *testing.T) {
+	s := newTestStore(t)
+	p, _ := s.CreateProject("LOFT", "", "")
+	nasT := builtInTypeID(t, s, "NAS")
+	swT := builtInTypeID(t, s, "Switch")
+	nas, _ := s.CreateDevice(p.ID, DeviceCreate{Name: "NAS", TypeID: &nasT, X: 0, Y: 0, Width: 100, Height: 35})
+	sw, _ := s.CreateDevice(p.ID, DeviceCreate{Name: "Switch", TypeID: &swT, X: 200, Y: 0, Width: 100, Height: 35})
+	rj45 := int64(5)
+	_, _ = s.CreateConnectionRequirement(p.ID, ConnectionRequirementCreate{
+		FromDeviceID: nas.ID, ToDeviceID: sw.ID, PreferredCableTypeID: &rj45,
+	})
+	_, _ = s.Solve(p.ID, true) // preview
+	cables, _ := s.ListCables(p.ID)
+	if len(cables) != 0 {
+		t.Errorf("preview wrote %d cables; want 0", len(cables))
+	}
+}
+
+func TestSolve_ApplyThenIdempotent(t *testing.T) {
+	s := newTestStore(t)
+	p, _ := s.CreateProject("LOFT", "", "")
+	nasT := builtInTypeID(t, s, "NAS")
+	swT := builtInTypeID(t, s, "Switch")
+	nas, _ := s.CreateDevice(p.ID, DeviceCreate{Name: "NAS", TypeID: &nasT, X: 0, Y: 0, Width: 100, Height: 35})
+	sw, _ := s.CreateDevice(p.ID, DeviceCreate{Name: "Switch", TypeID: &swT, X: 200, Y: 0, Width: 100, Height: 35})
+	rj45 := int64(5)
+	_, _ = s.CreateConnectionRequirement(p.ID, ConnectionRequirementCreate{
+		FromDeviceID: nas.ID, ToDeviceID: sw.ID, PreferredCableTypeID: &rj45,
+	})
+	r1, _ := s.Solve(p.ID, false)
+	if len(r1.CablesAdded) != 1 {
+		t.Fatalf("first apply: cables_added=%d, want 1", len(r1.CablesAdded))
+	}
+	r2, _ := s.Solve(p.ID, false)
+	if len(r2.CablesAdded) != 0 {
+		t.Errorf("second apply: cables_added=%d, want 0 (idempotent)", len(r2.CablesAdded))
+	}
+	if len(r2.CablesKept) != 1 {
+		t.Errorf("second apply: cables_kept=%d, want 1", len(r2.CablesKept))
+	}
+}
+
+func TestSolve_ManualCableReservesPort(t *testing.T) {
+	s := newTestStore(t)
+	p, _ := s.CreateProject("LOFT", "", "")
+	mouseT := builtInTypeID(t, s, "Mouse")
+	pcT := builtInTypeID(t, s, "PC")
+	mouse, _ := s.CreateDevice(p.ID, DeviceCreate{Name: "Mouse", TypeID: &mouseT, X: 0, Y: 0, Width: 100, Height: 35})
+	pc, _ := s.CreateDevice(p.ID, DeviceCreate{Name: "PC", TypeID: &pcT, X: 200, Y: 0, Width: 100, Height: 35})
+
+	// Manual cable USB Mouse↔PC: claims the only mouse USB port.
+	ports, _ := s.ListPortsForProject(p.ID)
+	var mouseUSB, pcUSB int64
+	for _, prt := range ports {
+		if prt.DeviceID == mouse.ID && prt.TypeID == 2 {
+			mouseUSB = prt.ID
+		}
+		if prt.DeviceID == pc.ID && prt.TypeID == 2 {
+			pcUSB = prt.ID
+			break
+		}
+	}
+	usb := int64(2)
+	_, _ = s.CreateCable(p.ID, CableCreate{
+		TypeID: usb,
+		From:   CableEndpoint{PortID: &mouseUSB},
+		To:     CableEndpoint{PortID: &pcUSB},
+		Auto:   false,
+	})
+
+	// Now add a requirement that also wants USB on the mouse → no free port.
+	_, _ = s.CreateConnectionRequirement(p.ID, ConnectionRequirementCreate{
+		FromDeviceID: mouse.ID, ToDeviceID: pc.ID, PreferredCableTypeID: &usb,
+	})
+	res, _ := s.Solve(p.ID, true)
+	if len(res.Unsatisfied) == 0 {
+		t.Errorf("expected unsatisfied req (manual cable should reserve the only mouse USB port)")
+	}
+}
+
+// -------------------------------------------------------- setup templates
+
+func TestApplyTemplate_LivingRoom(t *testing.T) {
+	s := newTestStore(t)
+	p, _ := s.CreateProject("LOFT", "", "")
+	tmpls, _ := s.ListSetupTemplates()
+	var lr SetupTemplate
+	for _, tm := range tmpls {
+		if tm.Name == "Living Room" {
+			lr = tm
+			break
+		}
+	}
+	if lr.ID == 0 {
+		t.Fatal("Living Room template not seeded")
+	}
+	res, err := s.ApplyTemplate(p.ID, lr.ID, ApplyTemplateOptions{})
+	if err != nil {
+		t.Fatalf("apply: %v", err)
+	}
+	if len(res.DevicesAdded) != 3 {
+		t.Errorf("devices added = %d, want 3 (TV, Soundbar, ChromeCast)", len(res.DevicesAdded))
+	}
+	if len(res.RequirementsAdded) != 2 {
+		t.Errorf("requirements added = %d, want 2 (TV↔Soundbar, TV↔ChromeCast)", len(res.RequirementsAdded))
+	}
+	// Ports were seeded as part of the device creation.
+	ports, _ := s.ListPortsForProject(p.ID)
+	if len(ports) < 6 { // TV(3) + Soundbar(2) + ChromeCast(2) = 7
+		t.Errorf("ports after template apply = %d, expected ≥6", len(ports))
+	}
+}
+
+func TestApplyTemplate_HomeOffice_ThenSolve(t *testing.T) {
+	s := newTestStore(t)
+	p, _ := s.CreateProject("LOFT", "", "")
+	tmpls, _ := s.ListSetupTemplates()
+	var ho SetupTemplate
+	for _, tm := range tmpls {
+		if tm.Name == "Home Office" {
+			ho = tm
+			break
+		}
+	}
+	if _, err := s.ApplyTemplate(p.ID, ho.ID, ApplyTemplateOptions{}); err != nil {
+		t.Fatalf("apply: %v", err)
+	}
+	res, err := s.Solve(p.ID, false)
+	if err != nil {
+		t.Fatalf("solve: %v", err)
+	}
+	if len(res.CablesAdded) != 3 {
+		t.Errorf("Home Office should solve to 3 cables (PC↔Screen, PC↔Keyboard, PC↔Mouse); got %d", len(res.CablesAdded))
+	}
+	if len(res.Unsatisfied) != 0 {
+		t.Errorf("unsatisfied = %+v, want []", res.Unsatisfied)
+	}
+}
+
+func TestApplyTemplate_NameCollisionSkipped(t *testing.T) {
+	s := newTestStore(t)
+	p, _ := s.CreateProject("LOFT", "", "")
+	pcT := builtInTypeID(t, s, "PC")
+	// Pre-create a device called "PC" so the Home Office template's PC collides.
+	_, _ = s.CreateDevice(p.ID, DeviceCreate{Name: "PC", TypeID: &pcT, X: 0, Y: 0, Width: 100, Height: 35})
+
+	tmpls, _ := s.ListSetupTemplates()
+	var ho SetupTemplate
+	for _, tm := range tmpls {
+		if tm.Name == "Home Office" {
+			ho = tm
+			break
+		}
+	}
+	res, _ := s.ApplyTemplate(p.ID, ho.ID, ApplyTemplateOptions{})
+	if len(res.SkippedDevices) == 0 {
+		t.Errorf("expected at least one skipped device for name collision; got %+v", res.SkippedDevices)
+	}
+	if len(res.RequirementsSkipped) == 0 {
+		t.Errorf("PC requirements should be skipped when PC device skipped; got %+v", res.RequirementsSkipped)
+	}
+}

internal/db/store.go

@@ -167,15 +167,36 @@ func (s *Store) Snapshot(id int64) (*Snapshot, error) {
 	if err != nil {
 		return nil, err
 	}
+	ios, err := s.ListIOMarkers(id)
+	if err != nil {
+		return nil, err
+	}
+	ports, err := s.ListPortsForProject(id)
+	if err != nil {
+		return nil, err
+	}
+	reqs, err := s.ListConnectionRequirements(id)
+	if err != nil {
+		return nil, err
+	}
+	cables, err := s.ListCables(id)
+	if err != nil {
+		return nil, err
+	}
+	bundles, err := s.ListBundles(id)
+	if err != nil {
+		return nil, err
+	}
 	return &Snapshot{
-		Project:    *p,
-		Frames:     frames,
-		Devices:    devices,
-		Ports:      []any{},
-		Cables:     []any{},
-		IOMarkers:  []any{},
-		Bundles:    []any{},
-		CableTypes: types,
+		Project:                *p,
+		Frames:                 frames,
+		Devices:                devices,
+		Ports:                  ports,
+		Cables:                 cables,
+		IOMarkers:              ios,
+		Bundles:                bundles,
+		CableTypes:             types,
+		ConnectionRequirements: reqs,
 	}, nil
 }
 

internal/server/cables.go

@@ -0,0 +1,225 @@
+package server
+
+import (
+	"encoding/json"
+	"errors"
+	"net/http"
+
+	"mgit.msbls.de/m/mcables/internal/db"
+)
+
+type cableEndpointBody struct {
+	PortID   *int64 `json:"port_id,omitempty"`
+	DeviceID *int64 `json:"device_id,omitempty"`
+	IOID     *int64 `json:"io_id,omitempty"`
+}
+
+type cableCreate struct {
+	TypeID int64             `json:"type_id"`
+	Label  string            `json:"label,omitempty"`
+	From   cableEndpointBody `json:"from"`
+	To     cableEndpointBody `json:"to"`
+	Auto   bool              `json:"auto,omitempty"`
+}
+
+type cablePatch struct {
+	TypeID *int64             `json:"type_id,omitempty"`
+	Label  *string            `json:"label,omitempty"`
+	From   *cableEndpointBody `json:"from,omitempty"`
+	To     *cableEndpointBody `json:"to,omitempty"`
+	Auto   *bool              `json:"auto,omitempty"`
+	// Promote=true asks the server to set auto=false when an auto cable
+	// is being PATCHed (slice 6 §5b.3 — explicit promote-to-manual).
+	Promote bool `json:"promote,omitempty"`
+}
+
+func toCableEndpoint(b cableEndpointBody) db.CableEndpoint {
+	return db.CableEndpoint{PortID: b.PortID, DeviceID: b.DeviceID, IOID: b.IOID}
+}
+
+func (h *handlers) listCables(w http.ResponseWriter, r *http.Request) {
+	pid, ok := parseInt64Path(r, "pid")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
+		return
+	}
+	cs, err := h.store.ListCables(pid)
+	if err != nil {
+		writeError(w, err, nil)
+		return
+	}
+	writeJSON(w, http.StatusOK, cs)
+}
+
+func (h *handlers) createCable(w http.ResponseWriter, r *http.Request) {
+	pid, ok := parseInt64Path(r, "pid")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
+		return
+	}
+	var body cableCreate
+	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+		writeError(w, errors.Join(db.ErrInvalidInput, err), nil)
+		return
+	}
+	c, err := h.store.CreateCable(pid, db.CableCreate{
+		TypeID: body.TypeID, Label: body.Label,
+		From: toCableEndpoint(body.From), To: toCableEndpoint(body.To),
+		Auto: body.Auto,
+	})
+	if err != nil {
+		writeError(w, err, nil)
+		return
+	}
+	writeJSON(w, http.StatusCreated, c)
+}
+
+func (h *handlers) patchCable(w http.ResponseWriter, r *http.Request) {
+	pid, ok := parseInt64Path(r, "pid")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
+		return
+	}
+	id, ok := parseInt64Path(r, "id")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "id must be a positive integer")
+		return
+	}
+	var body cablePatch
+	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+		writeError(w, errors.Join(db.ErrInvalidInput, err), nil)
+		return
+	}
+	u := db.CableUpdate{
+		TypeID: body.TypeID, Label: body.Label, Auto: body.Auto,
+	}
+	if body.From != nil {
+		ep := toCableEndpoint(*body.From)
+		u.From = &ep
+	}
+	if body.To != nil {
+		ep := toCableEndpoint(*body.To)
+		u.To = &ep
+	}
+	// Promote semantics: explicit promote=true OR (PATCH touched
+	// type/from/to AND the current cable is auto) → set auto=false.
+	if body.Promote {
+		f := false
+		u.Auto = &f
+	}
+	c, err := h.store.UpdateCable(pid, id, u)
+	if err != nil {
+		writeError(w, err, nil)
+		return
+	}
+	writeJSON(w, http.StatusOK, c)
+}
+
+func (h *handlers) deleteCable(w http.ResponseWriter, r *http.Request) {
+	pid, ok := parseInt64Path(r, "pid")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
+		return
+	}
+	id, ok := parseInt64Path(r, "id")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "id must be a positive integer")
+		return
+	}
+	if err := h.store.DeleteCable(pid, id); err != nil {
+		writeError(w, err, nil)
+		return
+	}
+	w.WriteHeader(http.StatusNoContent)
+}
+
+// ----------------------------------------------------------------- bundles
+
+type bundleCreate struct {
+	Name     string  `json:"name"`
+	CableIDs []int64 `json:"cable_ids"`
+}
+
+type bundlePatch struct {
+	Name     *string  `json:"name,omitempty"`
+	CableIDs *[]int64 `json:"cable_ids,omitempty"`
+}
+
+func (h *handlers) listBundles(w http.ResponseWriter, r *http.Request) {
+	pid, ok := parseInt64Path(r, "pid")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
+		return
+	}
+	bs, err := h.store.ListBundles(pid)
+	if err != nil {
+		writeError(w, err, nil)
+		return
+	}
+	writeJSON(w, http.StatusOK, bs)
+}
+
+func (h *handlers) createBundle(w http.ResponseWriter, r *http.Request) {
+	pid, ok := parseInt64Path(r, "pid")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
+		return
+	}
+	var body bundleCreate
+	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+		writeError(w, errors.Join(db.ErrInvalidInput, err), nil)
+		return
+	}
+	b, err := h.store.CreateBundle(pid, db.BundleCreate{
+		Name: body.Name, CableIDs: body.CableIDs, Auto: false,
+	})
+	if err != nil {
+		writeError(w, err, nil)
+		return
+	}
+	writeJSON(w, http.StatusCreated, b)
+}
+
+func (h *handlers) patchBundle(w http.ResponseWriter, r *http.Request) {
+	pid, ok := parseInt64Path(r, "pid")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
+		return
+	}
+	id, ok := parseInt64Path(r, "id")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "id must be a positive integer")
+		return
+	}
+	var body bundlePatch
+	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+		writeError(w, errors.Join(db.ErrInvalidInput, err), nil)
+		return
+	}
+	b, err := h.store.UpdateBundle(pid, id, db.BundleUpdate{
+		Name: body.Name, CableIDs: body.CableIDs,
+	})
+	if err != nil {
+		writeError(w, err, nil)
+		return
+	}
+	writeJSON(w, http.StatusOK, b)
+}
+
+func (h *handlers) deleteBundle(w http.ResponseWriter, r *http.Request) {
+	pid, ok := parseInt64Path(r, "pid")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
+		return
+	}
+	id, ok := parseInt64Path(r, "id")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "id must be a positive integer")
+		return
+	}
+	if err := h.store.DeleteBundle(pid, id); err != nil {
+		writeError(w, err, nil)
+		return
+	}
+	w.WriteHeader(http.StatusNoContent)
+}

internal/server/connection_requirements.go

@@ -0,0 +1,115 @@
+package server
+
+import (
+	"encoding/json"
+	"errors"
+	"net/http"
+
+	"mgit.msbls.de/m/mcables/internal/db"
+)
+
+type connReqCreate struct {
+	FromDeviceID         int64  `json:"from_device_id"`
+	ToDeviceID           int64  `json:"to_device_id"`
+	PreferredCableTypeID *int64 `json:"preferred_cable_type_id,omitempty"`
+	MustConnect          *bool  `json:"must_connect,omitempty"`
+	Notes                string `json:"notes,omitempty"`
+}
+
+// connReqPatch uses RawMessage for preferred_cable_type_id so the wire
+// tri-state ({} / null / int) is preserved.
+type connReqPatch struct {
+	PreferredCableTypeID json.RawMessage `json:"preferred_cable_type_id,omitempty"`
+	MustConnect          *bool           `json:"must_connect,omitempty"`
+	Notes                *string         `json:"notes,omitempty"`
+}
+
+func (h *handlers) listConnectionRequirements(w http.ResponseWriter, r *http.Request) {
+	pid, ok := parseInt64Path(r, "pid")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
+		return
+	}
+	rs, err := h.store.ListConnectionRequirements(pid)
+	if err != nil {
+		writeError(w, err, nil)
+		return
+	}
+	writeJSON(w, http.StatusOK, rs)
+}
+
+func (h *handlers) createConnectionRequirement(w http.ResponseWriter, r *http.Request) {
+	pid, ok := parseInt64Path(r, "pid")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
+		return
+	}
+	var body connReqCreate
+	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+		writeError(w, errors.Join(db.ErrInvalidInput, err), nil)
+		return
+	}
+	cr, err := h.store.CreateConnectionRequirement(pid, db.ConnectionRequirementCreate{
+		FromDeviceID:         body.FromDeviceID,
+		ToDeviceID:           body.ToDeviceID,
+		PreferredCableTypeID: body.PreferredCableTypeID,
+		MustConnect:          body.MustConnect,
+		Notes:                body.Notes,
+	})
+	if err != nil {
+		writeError(w, err, nil)
+		return
+	}
+	writeJSON(w, http.StatusCreated, cr)
+}
+
+func (h *handlers) patchConnectionRequirement(w http.ResponseWriter, r *http.Request) {
+	pid, ok := parseInt64Path(r, "pid")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
+		return
+	}
+	id, ok := parseInt64Path(r, "id")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "id must be a positive integer")
+		return
+	}
+	var body connReqPatch
+	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+		writeError(w, errors.Join(db.ErrInvalidInput, err), nil)
+		return
+	}
+	ctRef, err := parseFrameRef(body.PreferredCableTypeID)
+	if err != nil {
+		writeError(w, errors.Join(db.ErrInvalidInput, err), "preferred_cable_type_id must be an integer or null")
+		return
+	}
+	cr, err := h.store.UpdateConnectionRequirement(pid, id, db.ConnectionRequirementUpdate{
+		PreferredCableTypeID: ctRef,
+		MustConnect:          body.MustConnect,
+		Notes:                body.Notes,
+	})
+	if err != nil {
+		writeError(w, err, nil)
+		return
+	}
+	writeJSON(w, http.StatusOK, cr)
+}
+
+func (h *handlers) deleteConnectionRequirement(w http.ResponseWriter, r *http.Request) {
+	pid, ok := parseInt64Path(r, "pid")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
+		return
+	}
+	id, ok := parseInt64Path(r, "id")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "id must be a positive integer")
+		return
+	}
+	if err := h.store.DeleteConnectionRequirement(pid, id); err != nil {
+		writeError(w, err, nil)
+		return
+	}
+	w.WriteHeader(http.StatusNoContent)
+}

internal/server/device_types.go

@@ -0,0 +1,147 @@
+package server
+
+import (
+	"encoding/json"
+	"errors"
+	"net/http"
+
+	"mgit.msbls.de/m/mcables/internal/db"
+)
+
+type deviceTypePortBody struct {
+	CableTypeID int64  `json:"cable_type_id"`
+	LabelPrefix string `json:"label_prefix,omitempty"`
+	Count       int    `json:"count"`
+	Edge        string `json:"edge,omitempty"`
+	SortOrder   int    `json:"sort_order,omitempty"`
+}
+
+type deviceTypeCreate struct {
+	Name        string               `json:"name"`
+	Kind        string               `json:"kind,omitempty"`
+	Icon        string               `json:"icon,omitempty"`
+	Description string               `json:"description,omitempty"`
+	Ports       []deviceTypePortBody `json:"ports,omitempty"`
+}
+
+type deviceTypePatch struct {
+	Name        *string               `json:"name,omitempty"`
+	Kind        *string               `json:"kind,omitempty"`
+	Icon        *string               `json:"icon,omitempty"`
+	Description *string               `json:"description,omitempty"`
+	Ports       *[]deviceTypePortBody `json:"ports,omitempty"`
+}
+
+func portsToStore(body []deviceTypePortBody) []db.DeviceTypePortCreate {
+	out := make([]db.DeviceTypePortCreate, len(body))
+	for i, p := range body {
+		c := p.Count
+		if c <= 0 {
+			c = 1
+		}
+		out[i] = db.DeviceTypePortCreate{
+			CableTypeID: p.CableTypeID,
+			LabelPrefix: p.LabelPrefix,
+			Count:       c,
+			Edge:        p.Edge,
+			SortOrder:   p.SortOrder,
+		}
+	}
+	return out
+}
+
+// GET /api/device-types — built-in catalog only, read-only.
+func (h *handlers) listBuiltInDeviceTypes(w http.ResponseWriter, _ *http.Request) {
+	dts, err := h.store.ListBuiltInDeviceTypes()
+	if err != nil {
+		writeError(w, err, nil)
+		return
+	}
+	writeJSON(w, http.StatusOK, dts)
+}
+
+// GET /api/projects/:pid/device-types — built-ins + project-custom merged.
+func (h *handlers) listDeviceTypes(w http.ResponseWriter, r *http.Request) {
+	pid, ok := parseInt64Path(r, "pid")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
+		return
+	}
+	dts, err := h.store.ListDeviceTypesForProject(pid)
+	if err != nil {
+		writeError(w, err, nil)
+		return
+	}
+	writeJSON(w, http.StatusOK, dts)
+}
+
+func (h *handlers) createDeviceType(w http.ResponseWriter, r *http.Request) {
+	pid, ok := parseInt64Path(r, "pid")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
+		return
+	}
+	var body deviceTypeCreate
+	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+		writeError(w, errors.Join(db.ErrInvalidInput, err), nil)
+		return
+	}
+	dt, err := h.store.CreateDeviceType(pid, db.DeviceTypeCreate{
+		Name: body.Name, Kind: body.Kind, Icon: body.Icon,
+		Description: body.Description, Ports: portsToStore(body.Ports),
+	})
+	if err != nil {
+		writeError(w, err, nil)
+		return
+	}
+	writeJSON(w, http.StatusCreated, dt)
+}
+
+func (h *handlers) patchDeviceType(w http.ResponseWriter, r *http.Request) {
+	pid, ok := parseInt64Path(r, "pid")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
+		return
+	}
+	id, ok := parseInt64Path(r, "id")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "id must be a positive integer")
+		return
+	}
+	var body deviceTypePatch
+	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+		writeError(w, errors.Join(db.ErrInvalidInput, err), nil)
+		return
+	}
+	u := db.DeviceTypeUpdate{
+		Name: body.Name, Kind: body.Kind, Icon: body.Icon, Description: body.Description,
+	}
+	if body.Ports != nil {
+		converted := portsToStore(*body.Ports)
+		u.Ports = &converted
+	}
+	dt, err := h.store.UpdateDeviceType(pid, id, u)
+	if err != nil {
+		writeError(w, err, nil)
+		return
+	}
+	writeJSON(w, http.StatusOK, dt)
+}
+
+func (h *handlers) deleteDeviceType(w http.ResponseWriter, r *http.Request) {
+	pid, ok := parseInt64Path(r, "pid")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
+		return
+	}
+	id, ok := parseInt64Path(r, "id")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "id must be a positive integer")
+		return
+	}
+	if err := h.store.DeleteDeviceType(pid, id); err != nil {
+		writeError(w, err, nil)
+		return
+	}
+	w.WriteHeader(http.StatusNoContent)
+}

internal/server/frames_devices.go

@@ -110,6 +110,7 @@ func (h *handlers) deleteFrame(w http.ResponseWriter, r *http.Request) {
 type deviceCreate struct {
 	Name    string  `json:"name"`
 	FrameID *int64  `json:"frame_id,omitempty"`
+	TypeID  *int64  `json:"type_id,omitempty"`
 	Color   string  `json:"color,omitempty"`
 	X       float64 `json:"x"`
 	Y       float64 `json:"y"`
@@ -117,13 +118,14 @@ type deviceCreate struct {
 	Height  float64 `json:"height"`
 }
 
-// devicePatch uses a raw `json.RawMessage` for frame_id so we can tell
-// "key absent" (leave alone) from "key present and null" (set to NULL)
-// from "key present with an int" (move to that frame). Standard encoding
-// of nullable fields in JSON PATCH.
+// devicePatch uses a raw `json.RawMessage` for frame_id + type_id so we
+// can tell "key absent" (leave alone) from "key present and null"
+// (set to NULL) from "key present with an int" (move to that target).
+// Standard encoding of nullable fields in JSON PATCH.
 type devicePatch struct {
 	Name    *string         `json:"name,omitempty"`
 	FrameID json.RawMessage `json:"frame_id,omitempty"`
+	TypeID  json.RawMessage `json:"type_id,omitempty"`
 	Color   *string         `json:"color,omitempty"`
 	X       *float64        `json:"x,omitempty"`
 	Y       *float64        `json:"y,omitempty"`
@@ -173,7 +175,8 @@ func (h *handlers) createDevice(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	d, err := h.store.CreateDevice(pid, db.DeviceCreate{
-		Name: body.Name, FrameID: body.FrameID, Color: body.Color,
+		Name: body.Name, FrameID: body.FrameID, TypeID: body.TypeID,
+		Color: body.Color,
 		X: body.X, Y: body.Y, Width: body.Width, Height: body.Height,
 	})
 	if err != nil {
@@ -204,8 +207,13 @@ func (h *handlers) patchDevice(w http.ResponseWriter, r *http.Request) {
 		writeError(w, errors.Join(db.ErrInvalidInput, err), "frame_id must be an integer or null")
 		return
 	}
+	typeRef, err := parseFrameRef(body.TypeID)
+	if err != nil {
+		writeError(w, errors.Join(db.ErrInvalidInput, err), "type_id must be an integer or null")
+		return
+	}
 	d, err := h.store.UpdateDevice(pid, id, db.DeviceUpdate{
-		Name: body.Name, FrameID: ref, Color: body.Color,
+		Name: body.Name, FrameID: ref, TypeID: typeRef, Color: body.Color,
 		X: body.X, Y: body.Y, Width: body.Width, Height: body.Height,
 	})
 	if err != nil {

internal/server/handlers.go

@@ -42,6 +42,8 @@ func writeError(w http.ResponseWriter, err error, details any) {
 		writeJSON(w, http.StatusBadRequest, errorBody{Error: err.Error(), Details: details})
 	case errors.Is(err, db.ErrInvalidInput):
 		writeJSON(w, http.StatusBadRequest, errorBody{Error: err.Error(), Details: details})
+	case errors.Is(err, db.ErrForbidden):
+		writeJSON(w, http.StatusForbidden, errorBody{Error: err.Error(), Details: details})
 	default:
 		writeJSON(w, http.StatusInternalServerError, errorBody{Error: err.Error(), Details: details})
 	}

internal/server/io_markers.go

@@ -0,0 +1,109 @@
+package server
+
+import (
+	"encoding/json"
+	"errors"
+	"net/http"
+
+	"mgit.msbls.de/m/mcables/internal/db"
+)
+
+type ioMarkerCreate struct {
+	FrameID *int64  `json:"frame_id,omitempty"`
+	Label   string  `json:"label,omitempty"`
+	X       float64 `json:"x"`
+	Y       float64 `json:"y"`
+}
+
+// ioMarkerPatch mirrors devicePatch's frame_id tri-state — see
+// devicePatch + parseFrameRef in frames_devices.go for the wire format.
+type ioMarkerPatch struct {
+	Label   *string         `json:"label,omitempty"`
+	FrameID json.RawMessage `json:"frame_id,omitempty"`
+	X       *float64        `json:"x,omitempty"`
+	Y       *float64        `json:"y,omitempty"`
+}
+
+func (h *handlers) listIOMarkers(w http.ResponseWriter, r *http.Request) {
+	pid, ok := parseInt64Path(r, "pid")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
+		return
+	}
+	ms, err := h.store.ListIOMarkers(pid)
+	if err != nil {
+		writeError(w, err, nil)
+		return
+	}
+	writeJSON(w, http.StatusOK, ms)
+}
+
+func (h *handlers) createIOMarker(w http.ResponseWriter, r *http.Request) {
+	pid, ok := parseInt64Path(r, "pid")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
+		return
+	}
+	var body ioMarkerCreate
+	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+		writeError(w, errors.Join(db.ErrInvalidInput, err), nil)
+		return
+	}
+	m, err := h.store.CreateIOMarker(pid, db.IOMarkerCreate{
+		FrameID: body.FrameID, Label: body.Label, X: body.X, Y: body.Y,
+	})
+	if err != nil {
+		writeError(w, err, nil)
+		return
+	}
+	writeJSON(w, http.StatusCreated, m)
+}
+
+func (h *handlers) patchIOMarker(w http.ResponseWriter, r *http.Request) {
+	pid, ok := parseInt64Path(r, "pid")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
+		return
+	}
+	id, ok := parseInt64Path(r, "id")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "id must be a positive integer")
+		return
+	}
+	var body ioMarkerPatch
+	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+		writeError(w, errors.Join(db.ErrInvalidInput, err), nil)
+		return
+	}
+	ref, err := parseFrameRef(body.FrameID)
+	if err != nil {
+		writeError(w, errors.Join(db.ErrInvalidInput, err), "frame_id must be an integer or null")
+		return
+	}
+	m, err := h.store.UpdateIOMarker(pid, id, db.IOMarkerUpdate{
+		Label: body.Label, FrameID: ref, X: body.X, Y: body.Y,
+	})
+	if err != nil {
+		writeError(w, err, nil)
+		return
+	}
+	writeJSON(w, http.StatusOK, m)
+}
+
+func (h *handlers) deleteIOMarker(w http.ResponseWriter, r *http.Request) {
+	pid, ok := parseInt64Path(r, "pid")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
+		return
+	}
+	id, ok := parseInt64Path(r, "id")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "id must be a positive integer")
+		return
+	}
+	if err := h.store.DeleteIOMarker(pid, id); err != nil {
+		writeError(w, err, nil)
+		return
+	}
+	w.WriteHeader(http.StatusNoContent)
+}

internal/server/ports.go

@@ -0,0 +1,114 @@
+package server
+
+import (
+	"encoding/json"
+	"errors"
+	"net/http"
+
+	"mgit.msbls.de/m/mcables/internal/db"
+)
+
+type portCreate struct {
+	TypeID  int64   `json:"type_id"`
+	Label   string  `json:"label,omitempty"`
+	XOffset float64 `json:"x_offset"`
+	YOffset float64 `json:"y_offset"`
+}
+
+type portPatch struct {
+	TypeID  *int64   `json:"type_id,omitempty"`
+	Label   *string  `json:"label,omitempty"`
+	XOffset *float64 `json:"x_offset,omitempty"`
+	YOffset *float64 `json:"y_offset,omitempty"`
+}
+
+func (h *handlers) listPortsForDevice(w http.ResponseWriter, r *http.Request) {
+	pid, ok := parseInt64Path(r, "pid")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
+		return
+	}
+	id, ok := parseInt64Path(r, "id")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "id must be a positive integer")
+		return
+	}
+	ps, err := h.store.ListPortsForDevice(pid, id)
+	if err != nil {
+		writeError(w, err, nil)
+		return
+	}
+	writeJSON(w, http.StatusOK, ps)
+}
+
+func (h *handlers) createPort(w http.ResponseWriter, r *http.Request) {
+	pid, ok := parseInt64Path(r, "pid")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
+		return
+	}
+	id, ok := parseInt64Path(r, "id")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "id must be a positive integer")
+		return
+	}
+	var body portCreate
+	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+		writeError(w, errors.Join(db.ErrInvalidInput, err), nil)
+		return
+	}
+	p, err := h.store.CreatePort(pid, id, db.PortCreate{
+		TypeID: body.TypeID, Label: body.Label,
+		XOffset: body.XOffset, YOffset: body.YOffset,
+	})
+	if err != nil {
+		writeError(w, err, nil)
+		return
+	}
+	writeJSON(w, http.StatusCreated, p)
+}
+
+func (h *handlers) patchPort(w http.ResponseWriter, r *http.Request) {
+	pid, ok := parseInt64Path(r, "pid")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
+		return
+	}
+	id, ok := parseInt64Path(r, "id")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "id must be a positive integer")
+		return
+	}
+	var body portPatch
+	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+		writeError(w, errors.Join(db.ErrInvalidInput, err), nil)
+		return
+	}
+	p, err := h.store.UpdatePort(pid, id, db.PortUpdate{
+		TypeID: body.TypeID, Label: body.Label,
+		XOffset: body.XOffset, YOffset: body.YOffset,
+	})
+	if err != nil {
+		writeError(w, err, nil)
+		return
+	}
+	writeJSON(w, http.StatusOK, p)
+}
+
+func (h *handlers) deletePort(w http.ResponseWriter, r *http.Request) {
+	pid, ok := parseInt64Path(r, "pid")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
+		return
+	}
+	id, ok := parseInt64Path(r, "id")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "id must be a positive integer")
+		return
+	}
+	if err := h.store.DeletePort(pid, id); err != nil {
+		writeError(w, err, nil)
+		return
+	}
+	w.WriteHeader(http.StatusNoContent)
+}

internal/server/server.go

@@ -45,6 +45,51 @@ func New(store *db.Store, frontend fs.FS) http.Handler {
 	mux.HandleFunc("PATCH /api/projects/{pid}/devices/{id}", h.patchDevice)
 	mux.HandleFunc("DELETE /api/projects/{pid}/devices/{id}", h.deleteDevice)
 
+	// IO markers (project-scoped) — wall-outlet terminators
+	mux.HandleFunc("GET /api/projects/{pid}/io-markers", h.listIOMarkers)
+	mux.HandleFunc("POST /api/projects/{pid}/io-markers", h.createIOMarker)
+	mux.HandleFunc("PATCH /api/projects/{pid}/io-markers/{id}", h.patchIOMarker)
+	mux.HandleFunc("DELETE /api/projects/{pid}/io-markers/{id}", h.deleteIOMarker)
+
+	// Ports — slice 7 lets m add/edit/remove instance ports on a device.
+	mux.HandleFunc("GET /api/projects/{pid}/devices/{id}/ports", h.listPortsForDevice)
+	mux.HandleFunc("POST /api/projects/{pid}/devices/{id}/ports", h.createPort)
+	mux.HandleFunc("PATCH /api/projects/{pid}/ports/{id}", h.patchPort)
+	mux.HandleFunc("DELETE /api/projects/{pid}/ports/{id}", h.deletePort)
+
+	// Device-type catalog. Built-ins are read-only; project-custom rows
+	// support full CRUD scoped to the project.
+	mux.HandleFunc("GET /api/device-types", h.listBuiltInDeviceTypes)
+	mux.HandleFunc("GET /api/projects/{pid}/device-types", h.listDeviceTypes)
+	mux.HandleFunc("POST /api/projects/{pid}/device-types", h.createDeviceType)
+	mux.HandleFunc("PATCH /api/projects/{pid}/device-types/{id}", h.patchDeviceType)
+	mux.HandleFunc("DELETE /api/projects/{pid}/device-types/{id}", h.deleteDeviceType)
+
+	// Connection requirements — the solver's per-project input.
+	mux.HandleFunc("GET /api/projects/{pid}/connection-requirements", h.listConnectionRequirements)
+	mux.HandleFunc("POST /api/projects/{pid}/connection-requirements", h.createConnectionRequirement)
+	mux.HandleFunc("PATCH /api/projects/{pid}/connection-requirements/{id}", h.patchConnectionRequirement)
+	mux.HandleFunc("DELETE /api/projects/{pid}/connection-requirements/{id}", h.deleteConnectionRequirement)
+
+	// Cables — slice 6: solver writes here with auto=1; slice 7 lets m
+	// hand-draw with auto=0. PATCH supports `promote: true` to flip auto→0.
+	mux.HandleFunc("GET /api/projects/{pid}/cables", h.listCables)
+	mux.HandleFunc("POST /api/projects/{pid}/cables", h.createCable)
+	mux.HandleFunc("PATCH /api/projects/{pid}/cables/{id}", h.patchCable)
+	mux.HandleFunc("DELETE /api/projects/{pid}/cables/{id}", h.deleteCable)
+
+	// Bundles — manual + auto.
+	mux.HandleFunc("GET /api/projects/{pid}/bundles", h.listBundles)
+	mux.HandleFunc("POST /api/projects/{pid}/bundles", h.createBundle)
+	mux.HandleFunc("PATCH /api/projects/{pid}/bundles/{id}", h.patchBundle)
+	mux.HandleFunc("DELETE /api/projects/{pid}/bundles/{id}", h.deleteBundle)
+
+	// Solver + quick-fix combo + setup templates.
+	mux.HandleFunc("POST /api/projects/{pid}/solve", h.solve)
+	mux.HandleFunc("POST /api/projects/{pid}/devices/{id}/ports-and-resolve", h.portsAndResolve)
+	mux.HandleFunc("GET /api/setup-templates", h.listSetupTemplates)
+	mux.HandleFunc("POST /api/projects/{pid}/apply-template", h.applyTemplate)
+
 	// Frontend (embedded). Serve "/" → index.html via http.FileServerFS.
 	// Wrap in noCache so the browser revalidates with the ETag/Last-Modified
 	// the file server already emits — without this, browsers cache aggressively

internal/server/solver.go

@@ -0,0 +1,149 @@
+package server
+
+import (
+	"encoding/json"
+	"errors"
+	"net/http"
+
+	"mgit.msbls.de/m/mcables/internal/db"
+)
+
+func (h *handlers) solve(w http.ResponseWriter, r *http.Request) {
+	pid, ok := parseInt64Path(r, "pid")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
+		return
+	}
+	preview := r.URL.Query().Get("preview") == "1"
+	res, err := h.store.Solve(pid, preview)
+	if err != nil {
+		writeError(w, err, nil)
+		return
+	}
+	writeJSON(w, http.StatusOK, res)
+}
+
+// ports-and-resolve combo: POST a new port to a device + re-run solve in
+// the same request. Used by the inspector quick-fix.
+type portsAndResolveBody struct {
+	TypeID  int64   `json:"type_id"`
+	Label   string  `json:"label,omitempty"`
+	XOffset float64 `json:"x_offset,omitempty"`
+	YOffset float64 `json:"y_offset,omitempty"`
+}
+
+func (h *handlers) portsAndResolve(w http.ResponseWriter, r *http.Request) {
+	pid, ok := parseInt64Path(r, "pid")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
+		return
+	}
+	id, ok := parseInt64Path(r, "id")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "id must be a positive integer")
+		return
+	}
+	var body portsAndResolveBody
+	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+		writeError(w, errors.Join(db.ErrInvalidInput, err), nil)
+		return
+	}
+	res, err := h.store.PortsAndResolve(pid, id, body.TypeID, body.Label, body.XOffset, body.YOffset)
+	if err != nil {
+		writeError(w, err, nil)
+		return
+	}
+	writeJSON(w, http.StatusOK, res)
+}
+
+// -------------------------------------------------------- setup templates
+
+func (h *handlers) listSetupTemplates(w http.ResponseWriter, _ *http.Request) {
+	ts, err := h.store.ListSetupTemplates()
+	if err != nil {
+		writeError(w, err, nil)
+		return
+	}
+	writeJSON(w, http.StatusOK, ts)
+}
+
+type applyTemplateBody struct {
+	TemplateID    int64            `json:"template_id"`
+	NameOverrides map[string]string `json:"name_overrides,omitempty"`
+	SkipDevices   []int64          `json:"skip_devices,omitempty"`
+	OriginX       float64          `json:"origin_x,omitempty"`
+	OriginY       float64          `json:"origin_y,omitempty"`
+}
+
+func (h *handlers) applyTemplate(w http.ResponseWriter, r *http.Request) {
+	pid, ok := parseInt64Path(r, "pid")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
+		return
+	}
+	var body applyTemplateBody
+	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+		writeError(w, errors.Join(db.ErrInvalidInput, err), nil)
+		return
+	}
+	opts := db.ApplyTemplateOptions{
+		NameOverrides: map[int64]string{},
+		SkipDevices:   map[int64]bool{},
+		OriginX:       body.OriginX,
+		OriginY:       body.OriginY,
+	}
+	// JSON keys are strings; parse to int64.
+	for k, v := range body.NameOverrides {
+		var tid int64
+		_, _ = fmtSscan(k, &tid)
+		if tid > 0 {
+			opts.NameOverrides[tid] = v
+		}
+	}
+	for _, tid := range body.SkipDevices {
+		opts.SkipDevices[tid] = true
+	}
+	res, err := h.store.ApplyTemplate(pid, body.TemplateID, opts)
+	if err != nil {
+		writeError(w, err, nil)
+		return
+	}
+
+	// Auto-solve by default. ?solve=0 opts out for power users who want
+	// to inspect the seeded devices/requirements before the solver runs.
+	// This is THE fix for the v6 UX hole: m hit Apply, saw an empty
+	// canvas because nothing reloaded *and* nothing solved. With the
+	// frontend re-snapshotting after the POST returns and the response
+	// already carrying solver output, m sees the wired diagram in one click.
+	skipSolve := r.URL.Query().Get("solve") == "0"
+	combined := map[string]any{"template_apply": res}
+	if !skipSolve {
+		solveRes, err := h.store.Solve(pid, false)
+		if err != nil {
+			// Apply succeeded but Solve failed — don't 500 the whole
+			// call. Return template_apply with the solve error inline so
+			// the UI can recover (devices are there; m can re-solve).
+			combined["solve_error"] = err.Error()
+		} else {
+			combined["solve"] = solveRes
+		}
+	}
+	writeJSON(w, http.StatusOK, combined)
+}
+
+// fmtSscan parses a base-10 int from a string, returning (n, nil) on success.
+// Inline so handlers don't pull in strconv just for one call site.
+func fmtSscan(s string, out *int64) (int, error) {
+	var v int64
+	read := 0
+	for i := 0; i < len(s); i++ {
+		c := s[i]
+		if c < '0' || c > '9' {
+			break
+		}
+		v = v*10 + int64(c-'0')
+		read++
+	}
+	*out = v
+	return read, nil
+}

web/static/index.html

@@ -20,7 +20,9 @@
       </button>
     </div>
     <div class="topbar-spacer"></div>
-    <button type="button" id="btn-export" class="btn" disabled title="Slice 5">
+    <button type="button" id="btn-apply-template" class="btn">Apply template…</button>
+    <button type="button" id="btn-solve" class="btn btn-primary">Solve</button>
+    <button type="button" id="btn-export" class="btn" disabled title="Slice 8">
       Export
     </button>
   </header>
@@ -32,13 +34,19 @@
         <ul id="legend-list" class="legend-list"></ul>
         <button type="button" id="btn-add-type" class="btn btn-tiny">+ Type</button>
       </section>
+      <section class="requirements">
+        <h2 class="sidebar-heading">Requirements</h2>
+        <ul id="requirement-list" class="requirement-list"></ul>
+        <button type="button" id="btn-add-requirement" class="btn btn-tiny">+ Requirement</button>
+      </section>
       <section class="tools">
         <h2 class="sidebar-heading">Tools</h2>
         <ul class="tool-list">
           <li><button type="button" id="tool-frame"  class="btn btn-tiny" data-tool="frame">+ Frame</button></li>
           <li><button type="button" id="tool-device" class="btn btn-tiny" data-tool="device">+ Device</button></li>
-          <li><button type="button" class="btn btn-tiny" disabled title="Slice 4">+ IO</button></li>
-          <li><button type="button" class="btn btn-tiny" disabled title="Slice 3">Draw cable</button></li>
+          <li><button type="button" id="tool-io"     class="btn btn-tiny" data-tool="io">+ IO</button></li>
+          <li><button type="button" id="tool-req"    class="btn btn-tiny" data-tool="req">Drag req A→B</button></li>
+          <li><button type="button" id="tool-cable"  class="btn btn-tiny" data-tool="cable" title="Click a port to start, then click another port / device / IO marker">Draw cable</button></li>
         </ul>
       </section>
     </aside>
@@ -113,6 +121,91 @@
     </form>
   </dialog>
 
+  <!-- New device (slice 4: type-aware) -->
+  <dialog id="modal-new-device" class="modal" aria-labelledby="nd-title">
+    <form method="dialog" id="form-new-device">
+      <h2 id="nd-title">New device</h2>
+      <label class="field">
+        <span>Type</span>
+        <select id="nd-type" name="type_id" required>
+          <option value="">Loading…</option>
+        </select>
+      </label>
+      <label class="field">
+        <span>Name</span>
+        <input type="text" name="name" id="nd-name" required autocomplete="off" />
+      </label>
+      <p class="form-error" id="nd-error" hidden></p>
+      <div class="actions">
+        <button type="submit" class="btn btn-primary">Create</button>
+        <button type="button" class="btn" data-close>Cancel</button>
+      </div>
+    </form>
+  </dialog>
+
+  <!-- New / Edit connection requirement (slice 5) -->
+  <dialog id="modal-requirement" class="modal" aria-labelledby="rq-title">
+    <form method="dialog" id="form-requirement">
+      <h2 id="rq-title">New requirement</h2>
+      <label class="field">
+        <span>From device</span>
+        <select id="rq-from" name="from_device_id" required></select>
+      </label>
+      <label class="field">
+        <span>To device</span>
+        <select id="rq-to" name="to_device_id" required></select>
+      </label>
+      <label class="field">
+        <span>Cable type</span>
+        <select id="rq-cable" name="preferred_cable_type_id">
+          <option value="">— solver picks —</option>
+        </select>
+      </label>
+      <label class="field" style="flex-direction: row; align-items: center; gap: 8px;">
+        <input type="checkbox" id="rq-must" name="must_connect" checked />
+        <span style="font-size: 13px; color: var(--text);">Must connect (solver hard-requires this link)</span>
+      </label>
+      <label class="field">
+        <span>Notes</span>
+        <textarea name="notes" rows="2"></textarea>
+      </label>
+      <p class="form-error" id="rq-error" hidden></p>
+      <div class="actions">
+        <button type="submit" class="btn btn-primary">Save</button>
+        <button type="button" class="btn" data-close>Cancel</button>
+      </div>
+    </form>
+  </dialog>
+
+  <!-- Solve preview-diff (slice 6) -->
+  <dialog id="modal-solve" class="modal modal-wide" aria-labelledby="sv-title">
+    <div style="padding: 16px;">
+      <h2 id="sv-title">Solve preview</h2>
+      <div id="sv-body" class="sv-body"></div>
+      <div class="actions" style="margin-top: 12px;">
+        <button type="button" class="btn btn-primary" id="sv-apply">Apply</button>
+        <button type="button" class="btn" data-close>Cancel</button>
+      </div>
+    </div>
+  </dialog>
+
+  <!-- Apply template (slice 6) -->
+  <dialog id="modal-template" class="modal modal-wide" aria-labelledby="tp-title">
+    <form method="dialog" id="form-template">
+      <h2 id="tp-title">Apply setup template</h2>
+      <label class="field">
+        <span>Template</span>
+        <select id="tp-select" required></select>
+      </label>
+      <div id="tp-preview" class="tp-preview"></div>
+      <p class="form-error" id="tp-error" hidden></p>
+      <div class="actions">
+        <button type="submit" class="btn btn-primary">Apply</button>
+        <button type="button" class="btn" data-close>Cancel</button>
+      </div>
+    </form>
+  </dialog>
+
   <!-- Delete Project confirm -->
   <dialog id="modal-delete-project" class="modal" aria-labelledby="dp-title">
     <form method="dialog" id="form-delete-project">

web/static/style.css

@@ -211,7 +211,201 @@ body {
 .canvas-wrap.tool-frame  #canvas,
 .canvas-wrap.tool-frame  #canvas *,
 .canvas-wrap.tool-device #canvas,
-.canvas-wrap.tool-device #canvas * { cursor: crosshair !important; }
+.canvas-wrap.tool-device #canvas *,
+.canvas-wrap.tool-io     #canvas,
+.canvas-wrap.tool-io     #canvas *,
+.canvas-wrap.tool-port   #canvas,
+.canvas-wrap.tool-port   #canvas *,
+.canvas-wrap.tool-cable  #canvas,
+.canvas-wrap.tool-cable  #canvas * { cursor: crosshair !important; }
+
+.btn-link {
+  background: transparent;
+  border: 0;
+  color: var(--text-muted);
+  cursor: pointer;
+  font: inherit;
+  padding: 0 4px;
+  line-height: 1;
+}
+.btn-link:hover { color: var(--danger); }
+
+/* Highlight a port that's been picked as the cable-draw source. */
+.port-circle.cable-from {
+  stroke-width: 3;
+  filter: drop-shadow(0 0 4px var(--accent));
+}
+
+/* IO markers — diamonds. Power-by-convention, so the default fill is
+   the Power cable_type colour (#e03131). Rotated 45° rect is the
+   easiest way to draw a diamond that still hit-tests at the rotated
+   bounds (a <polygon> would also work; rect-with-rotate keeps the
+   same DOM shape as device/frame so the drag helpers reuse). */
+.io-marker {
+  fill: var(--danger);
+  fill-opacity: 0.18;
+  stroke: var(--danger);
+  stroke-width: 1.5;
+}
+.io-marker.selected,
+.io-marker:hover { stroke-width: 2.5; }
+.io-marker-label {
+  fill: var(--danger);
+  font-size: 11px;
+  font-weight: 600;
+  text-anchor: middle;
+  dominant-baseline: central;
+  pointer-events: none;
+  user-select: none;
+}
+
+/* Ports — small circles laid out along the device edge. The fill is
+   white so the port is visible regardless of the underlying device's
+   stroke; the stroke colour comes from the cable_type the port carries
+   (set inline in JS). */
+.port-circle {
+  fill: #fff;
+  stroke: var(--text);
+  stroke-width: 2;
+  cursor: crosshair;
+}
+
+.port-row {
+  display: grid;
+  grid-template-columns: 14px 1fr auto;
+  align-items: center;
+  gap: 6px;
+  font-size: 12px;
+  padding: 2px 0;
+}
+.port-row .swatch {
+  width: 10px;
+  height: 10px;
+  border-radius: 50%;
+  border: 1px solid rgba(0, 0, 0, 0.15);
+}
+.port-row .label { color: var(--text); }
+.port-row .conn  { color: var(--text-muted); font-size: 11px; }
+
+/* Requirements sidebar list */
+.requirement-list {
+  list-style: none;
+  padding: 0;
+  margin: 0 0 8px 0;
+  display: flex;
+  flex-direction: column;
+  gap: 2px;
+}
+.requirement-row {
+  display: grid;
+  grid-template-columns: 1fr auto;
+  align-items: center;
+  gap: 6px;
+  font-size: 12px;
+  padding: 3px 6px;
+  border-radius: var(--radius);
+  cursor: pointer;
+}
+.requirement-row:hover { background: var(--surface-2); }
+.requirement-row[aria-current="true"] {
+  background: var(--surface-2);
+  outline: 1px solid var(--accent);
+}
+.requirement-row .pair { color: var(--text); }
+.requirement-row .pair .type { color: var(--text-muted); font-size: 11px; }
+.requirement-row .badge {
+  font-size: 10px;
+  text-transform: uppercase;
+  letter-spacing: 0.04em;
+  padding: 2px 6px;
+  border-radius: 10px;
+  color: #fff;
+}
+.requirement-row .badge.must { background: var(--danger); }
+.requirement-row .badge.nice { background: var(--text-muted); }
+
+/* Tool-armed: drag-req tool cursor */
+.canvas-wrap.tool-req     #canvas,
+.canvas-wrap.tool-req     #canvas * { cursor: crosshair !important; }
+
+/* Drag-line preview while dragging from device A toward device B. */
+.req-drag-line {
+  stroke: var(--accent);
+  stroke-width: 2;
+  stroke-dasharray: 6 4;
+  fill: none;
+  pointer-events: none;
+}
+
+/* Cables on the canvas. Stroke colour comes from the cable_type;
+   solver-owned cables (auto=1) render with a slightly dashed pattern
+   so m can tell at a glance which the solver placed. */
+.cable-line {
+  fill: none;
+  stroke-width: 2;
+  cursor: pointer;
+}
+.cable-line.auto { stroke-dasharray: 8 3; }
+.cable-line:hover { stroke-width: 4; }
+.cable-line.selected { stroke-width: 4; }
+
+/* Solve preview-diff modal */
+.modal-wide { width: 560px; }
+.sv-body { font-size: 13px; }
+.sv-body h3 {
+  font-size: 11px;
+  text-transform: uppercase;
+  letter-spacing: 0.04em;
+  color: var(--text-muted);
+  margin: 12px 0 4px;
+}
+.sv-body ul {
+  list-style: none;
+  padding: 0;
+  margin: 0;
+  display: flex;
+  flex-direction: column;
+  gap: 2px;
+}
+.sv-body li {
+  padding: 4px 8px;
+  border-radius: var(--radius);
+  background: var(--surface-2);
+}
+.sv-body li.added   { border-left: 3px solid #2f9e44; }
+.sv-body li.removed { border-left: 3px solid var(--danger); text-decoration: line-through; }
+.sv-body li.unmet   { border-left: 3px solid #f59f00; }
+.sv-body li.unmet .quickfix {
+  display: inline-block;
+  margin-left: 8px;
+  font-size: 11px;
+  padding: 1px 6px;
+  background: var(--accent);
+  color: #fff;
+  border-radius: 10px;
+  cursor: pointer;
+}
+
+.tp-preview {
+  font-size: 13px;
+  background: var(--surface-2);
+  border-radius: var(--radius);
+  padding: 8px 12px;
+  margin: 8px 0;
+}
+.tp-preview h4 {
+  font-size: 11px;
+  text-transform: uppercase;
+  letter-spacing: 0.04em;
+  color: var(--text-muted);
+  margin: 6px 0 4px;
+}
+.tp-preview ul { list-style: none; padding: 0; margin: 0; }
+.tp-preview li { padding: 2px 0; }
+.tp-preview .skip {
+  margin-right: 6px;
+  font-size: 11px;
+}
 
 .rubber-band {
   fill: rgba(25, 113, 194, 0.08);