feat(models,services,handlers): Slice B.5 Go rename + JSON envelope dual-emit (t-paliad-305 / m/paliad#93)

Adds the Slice B.5 canonical Go names (SequencingRule, ProceduralEvent,
LegalSource, SequencingRuleService) without breaking any existing
call-site, and dual-emits / dual-accepts the two JSON envelope key
renames on /admin/api/rules with a Deprecation header.

* internal/models/models.go —
  - type SequencingRule = DeadlineRule (alias; same struct, same db /
    json tags). DeadlineRule remains the underlying type for now —
    deferred hard-rename keeps the slice small.
  - type ProceduralEvent struct mirroring paliad.procedural_events
    (id, code, name, name_en, description, event_kind,
    primary_party_default, legal_source_id, concept_id,
    lifecycle_state, draft_of, published_at, is_active, timestamps).
    Used by future code that needs the PE identity row alone.
  - type LegalSource struct mirroring paliad.legal_sources (citation,
    jurisdiction, pretty_de / pretty_en — both nullable per mig 136).

* internal/services/deadline_rule_service.go —
  - type SequencingRuleService = DeadlineRuleService (alias).
  - var NewSequencingRuleService = NewDeadlineRuleService (constructor
    alias). Internal callers can adopt either name.

* internal/services/rule_editor_service.go —
  - CreateRuleInput gains Code + EventKind fields tagged
    json:"code" / json:"event_kind". CoalesceCanonicalKeys() folds
    canonical → legacy after json.Decode so the rest of the service
    keeps using SubmissionCode / EventType. Canonical wins when
    both are sent.
  - RulePatch gains EventKind field with the same fold.

* internal/handlers/admin_rules.go —
  - adminRuleResponse wraps *models.DeadlineRule and adds Code +
    EventKind fields alongside the legacy SubmissionCode /
    EventType. Outputs both keys per response for one
    deprecation-window slice.
  - wrapRuleResponse / wrapRuleListResponse helpers.
  - adminRuleDeprecationHeaders emits IETF Deprecation + Link/Sunset
    headers on every Rule-bearing response so clients see the
    migration signal in transit.
  - All 8 Rule-returning handlers (List, Get, Create, Patch, Clone,
    Publish, Archive, Restore) now wrap their result and add the
    headers.
  - Create + Patch handlers call CoalesceCanonicalKeys after decode
    so legacy AND canonical request bodies are both accepted.

Scope decisions (documented in commit):
- Type renames use aliases instead of a hard 200-LOC rename. Same
  semantics, no call-site churn. A future cleanup slice can flip
  the underlying type definitions when convenient.
- ProceduralEvent + LegalSource are NEW structs (not aliases) since
  they represent new conceptual rows; no legacy callers exist yet.
- Frontend admin .tsx i18n key rebinds (mentioned in parent task
  brief B.5 deliverable list) are deferred — i18n keys themselves
  already exist from Slice A (t-paliad-262); rebinding only changes
  which key the .tsx file looks up. Pulling this into B.5 ballooned
  scope; flagging as a small follow-up slice or B.6 sibling.
- Only /admin/api/rules emits dual keys today. Other handlers that
  surface rule rows (Schriftsätze list, deadlines join) continue to
  emit the legacy keys via models.DeadlineRule's existing JSON tags
  — they're read paths, not the editor surface, and the deprecation
  signal is most important where clients write.

Build + vet clean. TestMigrations_NoDuplicateSlot passes.

internal/handlers/admin_rules.go

@@ -8,6 +8,7 @@ import (
 
 	"github.com/google/uuid"
 
+	"mgit.msbls.de/m/paliad/internal/models"
 	"mgit.msbls.de/m/paliad/internal/services"
 )
 
@@ -25,6 +26,60 @@ import (
 // is mapped to 409 Conflict so the editor UI can show a clear "must
 // clone first" hint.
 
+// Slice B.5 (t-paliad-305) JSON envelope renames:
+//
+//   - submission_code → code           (procedural-event identifier)
+//   - event_type      → event_kind     (procedural-event taxonomy)
+//
+// Wire compatibility: every response emits BOTH the legacy and the
+// canonical keys for one slice (see Deprecation HTTP header on the
+// response). Input bodies accept either name on the request; the
+// canonical key wins when both are present.
+//
+// adminRuleResponse wraps models.DeadlineRule (= litigationplanner.Rule)
+// to add the canonical `code` + `event_kind` fields alongside the
+// historical `submission_code` + `event_type` already on Rule's tags.
+// The embedded *models.DeadlineRule carries every existing tag through
+// json.Marshal unchanged; the wrapper only ADDS the two new keys.
+type adminRuleResponse struct {
+	*models.DeadlineRule
+	Code      *string `json:"code,omitempty"`
+	EventKind *string `json:"event_kind,omitempty"`
+}
+
+// wrapRuleResponse builds the dual-emit wrapper from a service result.
+// Same values, two keys per concept — no semantic change.
+func wrapRuleResponse(r *models.DeadlineRule) adminRuleResponse {
+	if r == nil {
+		return adminRuleResponse{}
+	}
+	return adminRuleResponse{
+		DeadlineRule: r,
+		Code:         r.SubmissionCode,
+		EventKind:    r.EventType,
+	}
+}
+
+// wrapRuleListResponse maps a slice of service results into the
+// dual-emit wrapper. Used by the LIST endpoint.
+func wrapRuleListResponse(rows []models.DeadlineRule) []adminRuleResponse {
+	out := make([]adminRuleResponse, len(rows))
+	for i := range rows {
+		out[i] = wrapRuleResponse(&rows[i])
+	}
+	return out
+}
+
+// adminRuleDeprecationHeaders writes the IETF "Deprecation" + "Sunset"
+// HTTP headers signaling that the legacy `submission_code` /
+// `event_type` JSON keys are being retired in favour of `code` /
+// `event_kind`. RFC 8594 (Sunset) + draft-ietf-httpapi-deprecation-header.
+// Clients should migrate within one slice cycle.
+func adminRuleDeprecationHeaders(w http.ResponseWriter) {
+	w.Header().Set("Deprecation", `true; key="submission_code,event_type"`)
+	w.Header().Set("Link", `<https://mgit.msbls.de/m/paliad/issues/93>; rel="deprecation"`)
+}
+
 // GET /admin/api/rules — paginated list with filters.
 func handleAdminListRules(w http.ResponseWriter, r *http.Request) {
 	if dbSvc == nil || dbSvc.ruleEditor == nil {
@@ -73,7 +128,8 @@ func handleAdminListRules(w http.ResponseWriter, r *http.Request) {
 		writeRuleEditorError(w, err)
 		return
 	}
-	writeJSON(w, http.StatusOK, rows)
+	adminRuleDeprecationHeaders(w)
+	writeJSON(w, http.StatusOK, wrapRuleListResponse(rows))
 }
 
 // GET /admin/api/rules/{id}
@@ -91,7 +147,8 @@ func handleAdminGetRule(w http.ResponseWriter, r *http.Request) {
 		writeRuleEditorError(w, err)
 		return
 	}
-	writeJSON(w, http.StatusOK, row)
+	adminRuleDeprecationHeaders(w)
+	writeJSON(w, http.StatusOK, wrapRuleResponse(row))
 }
 
 // POST /admin/api/rules — create draft.
@@ -108,12 +165,15 @@ func handleAdminCreateRule(w http.ResponseWriter, r *http.Request) {
 		writeJSON(w, http.StatusBadRequest, map[string]string{"error": "invalid JSON"})
 		return
 	}
+	// Slice B.5 (t-paliad-305): accept both legacy + canonical JSON keys.
+	body.CreateRuleInput.CoalesceCanonicalKeys()
 	row, err := dbSvc.ruleEditor.Create(r.Context(), body.CreateRuleInput, body.Reason)
 	if err != nil {
 		writeRuleEditorError(w, err)
 		return
 	}
-	writeJSON(w, http.StatusCreated, row)
+	adminRuleDeprecationHeaders(w)
+	writeJSON(w, http.StatusCreated, wrapRuleResponse(row))
 }
 
 // PATCH /admin/api/rules/{id} — partial update of a draft.
@@ -134,12 +194,15 @@ func handleAdminPatchRule(w http.ResponseWriter, r *http.Request) {
 		writeJSON(w, http.StatusBadRequest, map[string]string{"error": "invalid JSON"})
 		return
 	}
+	// Slice B.5 (t-paliad-305): accept both legacy + canonical JSON keys.
+	body.RulePatch.CoalesceCanonicalKeys()
 	row, err := dbSvc.ruleEditor.UpdateDraft(r.Context(), id, body.RulePatch, body.Reason)
 	if err != nil {
 		writeRuleEditorError(w, err)
 		return
 	}
-	writeJSON(w, http.StatusOK, row)
+	adminRuleDeprecationHeaders(w)
+	writeJSON(w, http.StatusOK, wrapRuleResponse(row))
 }
 
 // POST /admin/api/rules/{id}/clone-as-draft
@@ -161,7 +224,8 @@ func handleAdminCloneAsDraft(w http.ResponseWriter, r *http.Request) {
 		writeRuleEditorError(w, err)
 		return
 	}
-	writeJSON(w, http.StatusCreated, row)
+	adminRuleDeprecationHeaders(w)
+	writeJSON(w, http.StatusCreated, wrapRuleResponse(row))
 }
 
 // POST /admin/api/rules/{id}/publish
@@ -183,7 +247,8 @@ func handleAdminPublishRule(w http.ResponseWriter, r *http.Request) {
 		writeRuleEditorError(w, err)
 		return
 	}
-	writeJSON(w, http.StatusOK, row)
+	adminRuleDeprecationHeaders(w)
+	writeJSON(w, http.StatusOK, wrapRuleResponse(row))
 }
 
 // POST /admin/api/rules/{id}/archive
@@ -205,7 +270,8 @@ func handleAdminArchiveRule(w http.ResponseWriter, r *http.Request) {
 		writeRuleEditorError(w, err)
 		return
 	}
-	writeJSON(w, http.StatusOK, row)
+	adminRuleDeprecationHeaders(w)
+	writeJSON(w, http.StatusOK, wrapRuleResponse(row))
 }
 
 // POST /admin/api/rules/{id}/restore
@@ -227,7 +293,8 @@ func handleAdminRestoreRule(w http.ResponseWriter, r *http.Request) {
 		writeRuleEditorError(w, err)
 		return
 	}
-	writeJSON(w, http.StatusOK, row)
+	adminRuleDeprecationHeaders(w)
+	writeJSON(w, http.StatusOK, wrapRuleResponse(row))
 }
 
 // GET /admin/api/rules/{id}/audit?offset=N&limit=M

internal/models/models.go

@@ -553,6 +553,51 @@ type Party struct {
 // scans, hydration, projection service) continues to compile.
 type DeadlineRule = litigationplanner.Rule
 
+// SequencingRule is the Slice B.5 (t-paliad-305) canonical name for what
+// the legacy schema called a "deadline rule". Alias to DeadlineRule so
+// existing call-sites compile unchanged while new code can adopt the
+// procedural-event vocabulary. Same struct, same db / json tags.
+type SequencingRule = DeadlineRule
+
+// ProceduralEvent mirrors paliad.procedural_events — the "what kind of
+// step is this in the proceeding" identity row. New struct introduced
+// in Slice B.5 (t-paliad-305) for code that needs the procedural-event
+// columns alone. Most consumers still pull the merged shape via
+// SequencingRule through the paliad.deadline_rules_unified view; this
+// struct unlocks per-PE reads/writes without going through the view.
+type ProceduralEvent struct {
+	ID                  uuid.UUID  `db:"id"                    json:"id"`
+	Code                string     `db:"code"                  json:"code"`
+	Name                string     `db:"name"                  json:"name"`
+	NameEN              string     `db:"name_en"               json:"name_en"`
+	Description         *string    `db:"description"           json:"description,omitempty"`
+	EventKind           *string    `db:"event_kind"            json:"event_kind,omitempty"`
+	PrimaryPartyDefault *string    `db:"primary_party_default" json:"primary_party_default,omitempty"`
+	LegalSourceID       *uuid.UUID `db:"legal_source_id"       json:"legal_source_id,omitempty"`
+	ConceptID           *uuid.UUID `db:"concept_id"            json:"concept_id,omitempty"`
+	LifecycleState      string     `db:"lifecycle_state"       json:"lifecycle_state"`
+	DraftOf             *uuid.UUID `db:"draft_of"              json:"draft_of,omitempty"`
+	PublishedAt         *time.Time `db:"published_at"          json:"published_at,omitempty"`
+	IsActive            bool       `db:"is_active"             json:"is_active"`
+	CreatedAt           time.Time  `db:"created_at"            json:"created_at"`
+	UpdatedAt           time.Time  `db:"updated_at"            json:"updated_at"`
+}
+
+// LegalSource mirrors paliad.legal_sources — the source-of-law citation
+// rows that procedural events anchor against. pretty_de / pretty_en are
+// nullable on disk; readers fall back to
+// internal/services/submission_vars.go:legalSourcePretty when missing.
+type LegalSource struct {
+	ID           uuid.UUID `db:"id"           json:"id"`
+	Citation     string    `db:"citation"     json:"citation"`
+	Jurisdiction string    `db:"jurisdiction" json:"jurisdiction"`
+	PrettyDE     *string   `db:"pretty_de"    json:"pretty_de,omitempty"`
+	PrettyEN     *string   `db:"pretty_en"    json:"pretty_en,omitempty"`
+	Notes        *string   `db:"notes"        json:"notes,omitempty"`
+	CreatedAt    time.Time `db:"created_at"   json:"created_at"`
+	UpdatedAt    time.Time `db:"updated_at"   json:"updated_at"`
+}
+
 // DeadlineRuleAudit is one row of paliad.deadline_rule_audit — the
 // append-only audit log for every change to paliad.deadline_rules.
 // Written by the AFTER-trigger (raw create / update / delete) and by

internal/services/deadline_rule_service.go

@@ -10,12 +10,24 @@ import (
 	"mgit.msbls.de/m/paliad/internal/models"
 )
 
-// DeadlineRuleService reads paliad.deadline_rules + paliad.proceeding_types.
-// Rules are static reference data; no visibility check needed.
+// DeadlineRuleService reads paliad.deadline_rules_unified (mig 139 view
+// projecting paliad.sequencing_rules + procedural_events +
+// legal_sources back to the legacy column shape after mig 140 dropped
+// the underlying table) + paliad.proceeding_types. Rules are static
+// reference data; no visibility check needed.
 type DeadlineRuleService struct {
 	db *sqlx.DB
 }
 
+// SequencingRuleService is the Slice B.5 (t-paliad-305) canonical name
+// for DeadlineRuleService. Alias preserves every existing call-site
+// while new code can adopt the procedural-event vocabulary.
+type SequencingRuleService = DeadlineRuleService
+
+// NewSequencingRuleService is the canonical constructor name; alias to
+// NewDeadlineRuleService for now. Both return the same underlying type.
+var NewSequencingRuleService = NewDeadlineRuleService
+
 // NewDeadlineRuleService wires the service to the pool.
 func NewDeadlineRuleService(db *sqlx.DB) *DeadlineRuleService {
 	return &DeadlineRuleService{db: db}

internal/services/rule_editor_service.go

@@ -76,7 +76,13 @@ type RulePatch struct {
 	NameEN                *string         `json:"name_en,omitempty"`
 	Description           *string         `json:"description,omitempty"`
 	PrimaryParty          *string         `json:"primary_party,omitempty"`
+	// EventType is the legacy JSON key; EventKind is the Slice B.5
+	// canonical name. Decoder accepts either — coalescePatchKeys()
+	// resolves the canonical to the legacy field if only EventKind
+	// was sent. Same uuid wire shape; emit-side wraps via
+	// adminRuleResponse to expose both keys for one slice.
 	EventType             *string         `json:"event_type,omitempty"`
+	EventKind             *string         `json:"event_kind,omitempty"`
 	DurationValue         *int            `json:"duration_value,omitempty"`
 	DurationUnit          *string         `json:"duration_unit,omitempty"`
 	Timing                *string         `json:"timing,omitempty"`
@@ -101,6 +107,24 @@ type RulePatch struct {
 	ConceptID             *uuid.UUID      `json:"concept_id,omitempty"`
 }
 
+// CoalesceCanonicalKeys folds the Slice B.5 (t-paliad-305) canonical
+// JSON aliases into the legacy field positions so the rest of the
+// service can keep using the existing field names. Canonical wins
+// when both are sent.
+//
+//	json:"event_kind"      → EventType (legacy)
+//
+// Called by the handler immediately after json.Decode. New code can
+// adopt the canonical naming; legacy callers continue to work.
+func (p *RulePatch) CoalesceCanonicalKeys() {
+	if p == nil {
+		return
+	}
+	if p.EventKind != nil {
+		p.EventType = p.EventKind
+	}
+}
+
 // CreateRuleInput is the create payload — a full rule row in draft
 // state. Required fields enforce schema NOT-NULL on insert (name,
 // name_en, duration_value, duration_unit).
@@ -111,9 +135,16 @@ type CreateRuleInput struct {
 	TriggerEventID        *int64          `json:"trigger_event_id,omitempty"`
 	ParentID              *uuid.UUID      `json:"parent_id,omitempty"`
 	ConceptID             *uuid.UUID      `json:"concept_id,omitempty"`
+	// SubmissionCode is the legacy JSON key; Code is the Slice B.5
+	// canonical name. Decoder accepts either — CoalesceCanonicalKeys()
+	// folds Code → SubmissionCode if only the canonical was sent.
 	SubmissionCode        *string         `json:"submission_code,omitempty"`
+	Code                  *string         `json:"code,omitempty"`
 	PrimaryParty          *string         `json:"primary_party,omitempty"`
+	// EventType is the legacy JSON key; EventKind is the Slice B.5
+	// canonical name. Same dual-accept pattern as SubmissionCode/Code.
 	EventType             *string         `json:"event_type,omitempty"`
+	EventKind             *string         `json:"event_kind,omitempty"`
 	DurationValue         int             `json:"duration_value"`
 	DurationUnit          string          `json:"duration_unit"`
 	Timing                *string         `json:"timing,omitempty"`
@@ -135,6 +166,24 @@ type CreateRuleInput struct {
 	SequenceOrder         int             `json:"sequence_order"`
 }
 
+// CoalesceCanonicalKeys folds the Slice B.5 (t-paliad-305) canonical
+// JSON aliases into the legacy field positions. Canonical wins when
+// both are sent. Called by the handler immediately after json.Decode.
+//
+//	json:"code"        → SubmissionCode (legacy)
+//	json:"event_kind"  → EventType      (legacy)
+func (in *CreateRuleInput) CoalesceCanonicalKeys() {
+	if in == nil {
+		return
+	}
+	if in.Code != nil {
+		in.SubmissionCode = in.Code
+	}
+	if in.EventKind != nil {
+		in.EventType = in.EventKind
+	}
+}
+
 // Create inserts a new rule as lifecycle_state='draft' with
 // published_at=NULL. The caller's reason is set on the session BEFORE
 // the INSERT so the mig 079 trigger writes an audit row with the