docs(agents): family-lens enforcement moves to RLS — one source

Approves and lands the doctrine rewrite from the verified rollout:
RLS on media_items IS the enforcement (policy joins library_visibility
on app.user_id, declared per transaction by ScopedDB); new
media-listing queries and endpoints need no visibility plumbing.
Documents the three identity bridge sites, background-job identities,
the FORCE/owner role and db-init provisioning, per-boot schema
idempotency, and the two auditors (TestRlsInvariant + tests/ui).
Item-scoped gates may answer 404 as well as 403 (contract_pins
2026-10-29). History records the convention-era leak the dashboard
section queries carried.

AGENTS.md

@@ -106,30 +106,50 @@ inside quoted attribute values (gotcha #1 below), so dynamic
 ## Library visibility (family-lens rule) — ALWAYS apply
 
 Per-user library visibility (`library_visibility` table, default-ALLOW:
-every user sees every library unless an admin hides one) must be
-enforced on **every endpoint that returns media metadata or content**.
-It is NOT automatic — enforcement is per-handler.
+every user sees every library unless an admin hides one) is enforced by
+**Postgres RLS** — one source of truth: the labeled policy block in
+`database/schema/schema.sql` + the runtime role
+(`database/schema/z_rls_role.sh`).
 
-- **New endpoints that list/filter media or series** MUST filter by the
-  requesting user's visible-library set, and MUST reject an explicit
-  `library_id` outside that set with 403 (never silently pass).
-- Helpers (do not hand-roll):
-  - `handlers`: `(*MediaHandler).visibleLibrarySet` /
-    `(*SeriesHandler).visibleLibrarySet` — membership map + id slice.
-  - `router`: `visibleLibraryIDsFor` — same for SSR routes.
-  - `resolveLibrary` (helpers.go) only honors requested library ids
-    inside the visible set.
-- SQL pattern: `AND (sqlc.narg('visible_library_ids')::uuid[] IS NULL OR
-  library_id = ANY(sqlc.narg('visible_library_ids')::uuid[]))` — see
-  `ListMediaItems`, `GetDistinctSeries`, `SearchMediaItems`.
-- Content endpoints (file bytes, page images) additionally gate per item
-  like `ReaderHandler.ensureItemVisible` / the download endpoint.
-- Tests must pin visibility: hidden library → 403 on the endpoint, and
-  absent from unscoped aggregates.
+- **The engine is the enforcement.** Every `media_items` read is
+  filtered by the policy, which joins `library_visibility` on the
+  per-transaction GUC `app.user_id`. New media-listing queries need
+  NO visibility clause; new endpoints need NO visibility plumbing.
+- **The app declares identity; it never computes visibility.** All
+  sqlc statements run through `ScopedDB`
+  (`internal/database/scoped.go`), which declares `app.user_id` from
+  the stdlib request context. Three bridge sites put it there:
+  `router.go` JWT, `router.go` cookie/device, and
+  `middleware/device_auth.go` (KOReader/Kobo sync devices). A media
+  read on a detached `context.Background()` RAISES — thread the
+  request context or the acting identity (see conflicts.go and
+  analytics.go for the pattern).
+- **Background jobs declare the acting identity** before detached
+  work: scan jobs carry the library owner / first-admin fallback
+  (the job Context carries it — `ScanFolders` self-declares the
+  configured admin), the hash backfill runs as first admin. The sync
+  queue processor needs nothing (`sync_queue` is not RLS-governed).
+- **NEVER**: session-scoped `app.user_id` (pooled-connection identity
+  bleed); a bypass flag; connecting the app as the bootstrap
+  superuser (superusers bypass RLS unconditionally — `DATABASE_USER`
+  stays `bookhoard_srv`; the `db-init` compose service provisions the
+  role on every startup).
+- **schema.sql re-runs on EVERY boot** (executeSchema) — everything
+  added to it must be idempotent (`DROP .. IF EXISTS` + `CREATE`).
+  The migration tx declares a synthetic identity
+  (`schemaMigrationIdentity`) because the schema's own dedup block
+  reads `media_items`.
+- **Auditors**: `TestRlsInvariant` (API black-box — add new
+  media-returning surfaces to it; loosening requires a
+  docs/contract_pins.md entry) and the Playwright sweep (`tests/ui`,
+  new pages/controls go into `tests/ui/COVERAGE.md`). Item-scoped
+  gates may answer 404 as well as 403 (row invisible vs Go-level
+  check — contract_pins 2026-10-29).
 
 History: 2026-10-13 (`431fec0`) the series/media listing surfaces
-leaked hidden libraries to any authenticated account — series endpoints
-were name-only across ALL libraries. Fixed; do not regress.
+leaked hidden libraries; **2026-10-29 enforcement moved to RLS** — the
+dashboard section queries had silently never carried the clauses,
+and the invariant test went red → green and stays as the auditor.
 
 ## Tests