docs(caldav): fold m's decisions on the 6 open Qs into the design (t-paliad-212)

Addendum after §10 captures m's picks (2026-05-19, via AskUserQuestion):
§8.1 bidirectional default: YES; §8.2 personal_only: KEEP first-class;
§8.3 MKCALENDAR: Slice 2 with Google-degrade; §8.4 soft caps: NONE in
v1 (add later if telemetry warrants); §8.5 admin view: don't ship;
§8.6 approval-flow remote-edit gap: separate task under t-138.

Net effect: drops the 20-warn/80-block UI guards from §6 and the
`read_only` flag from §3; Slice 2 gains MKCALENDAR + binding-count
telemetry; §8.6 fix filed separately so multi-cal slices stay clean.

docs/design-caldav-multi-calendar-2026-05-19.md

@@ -3,7 +3,7 @@
 **Task:** t-paliad-212
 **Inventor:** leibniz (2026-05-19)
 **Branch:** mai/leibniz/inventor-caldav-multi
-**Status:** READY FOR REVIEW
+**Status:** READY FOR REVIEW — m's decisions on the §8 open questions captured in the addendum below (2026-05-19).
 
 ---
 
@@ -551,3 +551,47 @@ Google. These are easy to add later if the data says so.)
 - [Fastmail — Account limits](https://www.fastmail.help/hc/en-us/articles/1500000277382-Account-limits) — 100k events/user, no documented calendar count cap.
 - [Nextcloud admin manual — Calendar / CalDAV](https://docs.nextcloud.com/server/stable/admin_manual/groupware/calendar.html) — default 30, configurable, 10/hr rate limit.
 - Live verification against `internal/services/caldav_*.go` and `paliad.user_caldav_config` / `paliad.appointments` schema on the youpc Supabase instance.
+
+---
+
+## Addendum — m's decisions (2026-05-19)
+
+Walked through §8.1–§8.6 with m via AskUserQuestion. Decisions are
+locked in for the coder shift; revisit only on Slice-3 feedback.
+
+| Q | Decision | Implication for the slice plan |
+|---|---|---|
+| **§8.1 — Bidirectional default** | **Yes — bidirectional by default** | No `read_only` flag in Slice 1–3. Multi-cal inherits Phase F's last-write-wins / foreign-UID-skip semantics unchanged. Per-binding `read_only` only added later if a real use case shows up. |
+| **§8.2 — `personal_only` scope** | **Keep — first-class scope** | Ships in Slice 2 as one of the picker's radio options (`Everything I can see` / `Personal only` / `One project`). One enum value, one `ForBinding()` branch. |
+| **§8.3 — MKCALENDAR timing** | **Slice 2 with Google-degrade UX** | Slice 2 includes `POST /api/caldav-mkcalendar` + capability probe. Google users get a friendly "create the calendar in your Google UI, paste the URL" fallback. iCloud / Fastmail / Nextcloud / Radicale / Baikal / SOGo get one-click "Create new calendar". |
+| **§8.4 — Soft caps** | **No caps in v1, add later if data warrants** | Drop the 20-warn / 80-block UI guards from §6. Instrument `count(*)` on `user_calendar_bindings` per user as a Slice 2 telemetry add. Revisit if/when real distributions land. |
+| **§8.5 — `/admin/caldav-bindings` view** | **Don't ship in v1** | Stays out of the slice plan. Support debugging goes via Supabase SQL until a real ticket lands. Frees Slice 4 polish for the legacy-column drop only. |
+| **§8.6 — Approval-flow remote-edit gap** | **Separate task under t-138** | Out of scope for all four multi-cal slices. File the gap as a new `t-paliad-*` follow-up under t-138 so multi-cal stays clean and reverter-friendly. Pre-existing hole, surfaced not fixed. |
+
+### Net effect on §7 slice plan
+
+- **Slice 1** unchanged — schema + backfill, behaviour-equivalent.
+- **Slice 2** = picker UI + `REPORT calendar-multiget` + **MKCALENDAR
+  with capability probe + Google-degrade message** + binding-count
+  telemetry. No `read_only` flag, no soft caps, no admin view.
+  Scopes enabled: `all_visible`, `personal_only`, `project`.
+- **Slice 3** = hierarchy scopes (`client` / `litigation` / `patent` / `case`)
+  + per-project quick-adds. **No** approval-gap fix folded in.
+- **Slice 4** = drop legacy `appointments.caldav_uid` / `caldav_etag`.
+  Soft-cap banners only if Slice 2 telemetry says we need them.
+
+### Net effect on §3 schema
+
+No change. `user_calendar_bindings` still ships with the full
+`scope_kind` enum (including `personal_only`). `appointment_caldav_targets`
+unchanged. No `read_only` column in v1.
+
+### Follow-ups to file as separate tasks
+
+1. **`t-paliad-*` (under t-138):** approval-flow + CalDAV remote-edit
+   gap. `ApplyRemoteUpdate` bypasses the approval gate when an external
+   client edits a pending-approval event. Pre-existing in single-cal
+   Phase F. Owner: t-138 maintainer.
+2. **(maybe) `t-paliad-*`:** soft-cap UI if Slice 2 telemetry shows
+   any user near the iCloud-100 / Nextcloud-30 envelope. Not pre-filed
+   — only opens if data warrants.