wip(rls): ScopedDB + rls package + schema policies + echo bridge [pin compiling state]

Phase 3 of the RLS plan, pinned mid-flight because a parallel writer
was actively editing cmd/server/tests/rls_visibility_test.go (A14):
the file flip-flopped between two implementations and gained a compile
error after the previous commit. This snapshot makes the whole tree
compile; functional verification (two-boot gate, invariant green,
full suite) lands in the next commit(s).

- internal/rls: typed ctx keys — user identity (bridged from echo by
  the router) and an INTERNAL marker whose semantics grant nothing:
  no GUC is declared, so policy'd tables still raise at the engine;
  only RLS-ungoverned tables (system_settings, users counts) work for
  user-less startup paths (settings registry Load, CountAdmins).
- internal/database/scoped.go: DBTX decorator — per-statement tx,
  commit-on-Close (:many) / commit-on-Scan (:one), error paths always
  terminate the tx, refusal before SQL when no identity and not
  internal.
- database/schema/schema.sql: idempotent policy block (DROP IF EXISTS
  + CREATE — schema.sql re-runs every boot): ENABLE + FORCE, read
  policy exactly mirroring COALESCE(is_visible,true), permissive
  per-command write stand-ins (FOR ALL would OR into SELECT).
- router.go: RLS bridge at BOTH c.Set("user") sites (JWT + device
  auth) — echo-local storage never reaches the stdlib ctx.
- main.go + test harness: database.New over ScopedDB at both wiring
  sites; startup reads use rls.WithInternal.

database/schema/schema.sql

@@ -1877,3 +1877,72 @@ CREATE INDEX IF NOT EXISTS idx_hash_conflicts_status ON hash_conflicts(status);
 
 -- Widen for databases created before the resolution format settled (no-op otherwise)
 ALTER TABLE hash_conflicts ALTER COLUMN resolution TYPE VARCHAR(50);
+
+-- ============================================================
+-- RLS: PER-USER LIBRARY VISIBILITY (ONE SOURCE OF TRUTH)
+-- Plan: ~/.opencode/plan/server-rls-library-visibility.md REV 2.
+-- The policy joins library_visibility DIRECTLY — the same table the
+-- visibility UI writes. The app declares the acting user per
+-- transaction via the LOCAL GUC app.user_id (ScopedDB, set_config
+-- is_local=true). Unset identity FAILS LOUD, never fails open:
+--   - GUC never set in the session -> current_setting() raises
+--     ("unrecognized configuration parameter")
+--   - GUC set-then-transaction-ended -> reverts to '' -> the ::uuid
+--     cast raises
+--   - NULL GUC (unreachable via ScopedDB) -> IS NOT NULL guard ->
+--     zero rows (fail-closed)
+-- The runtime role bookhoard_srv OWNS these tables and is subject to
+-- the policies via FORCE (z_rls_role.sh). Never connect the app as
+-- the bootstrap superuser — superusers bypass RLS unconditionally.
+-- IDEMPOTENT: schema.sql re-executes on EVERY app boot
+-- (database.Initialize -> executeSchema); DROP .. IF EXISTS + CREATE
+-- matches the repo's trigger idiom. DO NOT make this block
+-- non-idempotent — the second boot would brick the app.
+-- ============================================================
+
+DROP POLICY IF EXISTS p_media_items_visible ON media_items;
+DROP POLICY IF EXISTS p_media_items_insert ON media_items;
+DROP POLICY IF EXISTS p_media_items_update ON media_items;
+DROP POLICY IF EXISTS p_media_items_delete ON media_items;
+
+ALTER TABLE media_items ENABLE ROW LEVEL SECURITY;
+ALTER TABLE media_items FORCE ROW LEVEL SECURITY;
+
+-- READ policy: EXACTLY the app's COALESCE(lv.is_visible, true)
+-- semantics — row absent -> visible; row true -> visible; row false
+-- -> hidden. No new index needed: library_visibility's
+-- UNIQUE(user_id, library_id) constraint already indexes the join.
+CREATE POLICY p_media_items_visible ON media_items
+  FOR SELECT
+  USING (
+    current_setting('app.user_id') IS NOT NULL
+    AND NOT EXISTS (
+      SELECT 1 FROM library_visibility lv
+      WHERE lv.user_id = current_setting('app.user_id')::uuid
+        AND lv.library_id = media_items.library_id
+        AND lv.is_visible = false
+    )
+  );
+
+-- WRITE policies: PERMISSIVE STAND-INS for the deferred scoped write
+-- lens. MANDATORY at ENABLE time — with RLS enabled and no applicable
+-- policy, INSERT fails (42501) and UPDATE/DELETE silently affect zero
+-- rows, bricking the media scanner. Per-command split is deliberate:
+-- a single FOR ALL policy with USING (true) would OR into SELECT and
+-- disable the read policy above. Writes still need SELECT visibility
+-- of the target rows (the read policy governs that), which internal
+-- identities satisfy (they have no hidden rows).
+-- ON CONFLICT upserts (scanner: (library_id, file_path)) need the
+-- conflicting row SELECT-visible to the acting identity — holds for
+-- every internal identity by construction.
+CREATE POLICY p_media_items_insert ON media_items
+  FOR INSERT WITH CHECK (true);
+CREATE POLICY p_media_items_update ON media_items
+  FOR UPDATE USING (true) WITH CHECK (true);
+CREATE POLICY p_media_items_delete ON media_items
+  FOR DELETE USING (true);
+
+-- Other tables: NONE. collection_items reaches media only via INNER
+-- JOIN media_items (the join drops filtered rows). collections
+-- metadata (book_count) is a separate counts question — plan A13.
+-- ============================================================