feat(state-hub): Interface Change Registry (CUST-WP-0033 T01-T06)

Adds first-class tracking for API and interface mutations across the
agent ecosystem. Breaking changes are documented, affected repos are
notified via inbox, and agents discover pending changes at session
start via the dispatch endpoint.

- Migration q4l5m6n7o8p9: interface_changes table
- Model/schema: InterfaceChange with draft→published→resolved lifecycle
- Router: POST/GET/PATCH /interface-changes/, /publish, /resolve actions
  (auto-notify affected repo agents on publish; progress event on origin)
- Dispatch: GET /repos/{slug}/dispatch now returns pending_interface_changes
- MCP tools: register_interface_change, list_interface_changes,
  publish_interface_change, resolve_interface_change
- Dashboard: /interface-changes page with type badges, planned calendar,
  published cards, and draft table
- EP-CUST-ICR-001 registered: webhook subscriptions (deliberately deferred)

First record: trailing-slash normalisation (2026-04-26), published,
affecting repo-registry — visible in repo-registry dispatch immediately.

223 tests passing.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

api/routers/repos.py

@@ -16,6 +16,7 @@ from api.database import get_session
 from api.doi_engine import compute_fingerprint, evaluate as _doi_evaluate
 from api.models.doi_cache import DOICache
 from api.models.domain import Domain
+from api.models.interface_change import InterfaceChange
 from api.models.managed_repo import ManagedRepo
 from api.models.repo_goal import RepoGoal
 from api.models.tpsc import TPSCSnapshot
@@ -25,6 +26,7 @@ from api.schemas.doi import DoICriterion, DoIReport, DoISummaryEntry
 from api.schemas.managed_repo import (
     DispatchTask,
     DispatchWorkstream,
+    PendingInterfaceChange,
     RepoCreate,
     RepoDispatch,
     RepoPathRegister,
@@ -468,11 +470,33 @@ async def get_repo_dispatch(
             )
         )
 
+    # Published interface changes that affect this repo and are not yet resolved
+    ic_result = await session.execute(
+        select(InterfaceChange).where(
+            InterfaceChange.status == "published",
+            InterfaceChange.affected_repo_slugs.contains([slug]),
+        ).order_by(InterfaceChange.published_at.desc())
+    )
+    pending_changes = [
+        PendingInterfaceChange(
+            id=ic.id,
+            title=ic.title,
+            change_type=ic.change_type,
+            interface_type=ic.interface_type,
+            origin_repo_slug=ic.repo.slug,
+            affected_paths=ic.affected_paths or [],
+            planned_for=ic.planned_for,
+            published_at=ic.published_at,
+        )
+        for ic in ic_result.scalars().all()
+    ]
+
     return RepoDispatch(
         repo_slug=slug,
         active_goal=active_goal,
         active_workstreams=dispatch_workstreams,
         human_interventions=all_interventions,
+        pending_interface_changes=pending_changes,
         last_state_synced_at=repo.last_state_synced_at,
     )