diff --git a/internal/adapters/store/migrations/003_rls.down.sql b/internal/adapters/store/migrations/003_rls.down.sql
new file mode 100644
index 0000000..87cdf0f
--- /dev/null
+++ b/internal/adapters/store/migrations/003_rls.down.sql
@@ -0,0 +1,23 @@
+DROP POLICY IF EXISTS sink_deliveries_isolation ON sink_deliveries;
+ALTER TABLE sink_deliveries NO FORCE ROW LEVEL SECURITY;
+ALTER TABLE sink_deliveries DISABLE ROW LEVEL SECURITY;
+
+DROP POLICY IF EXISTS summary_actions_isolation ON summary_actions;
+ALTER TABLE summary_actions NO FORCE ROW LEVEL SECURITY;
+ALTER TABLE summary_actions DISABLE ROW LEVEL SECURITY;
+
+DROP POLICY IF EXISTS summaries_isolation ON summaries;
+ALTER TABLE summaries NO FORCE ROW LEVEL SECURITY;
+ALTER TABLE summaries DISABLE ROW LEVEL SECURITY;
+
+DROP POLICY IF EXISTS transcripts_isolation ON transcripts;
+ALTER TABLE transcripts NO FORCE ROW LEVEL SECURITY;
+ALTER TABLE transcripts DISABLE ROW LEVEL SECURITY;
+
+DROP POLICY IF EXISTS videos_isolation ON videos;
+ALTER TABLE videos NO FORCE ROW LEVEL SECURITY;
+ALTER TABLE videos DISABLE ROW LEVEL SECURITY;
+
+DROP POLICY IF EXISTS users_isolation ON users;
+ALTER TABLE users NO FORCE ROW LEVEL SECURITY;
+ALTER TABLE users DISABLE ROW LEVEL SECURITY;
diff --git a/internal/adapters/store/migrations/003_rls.up.sql b/internal/adapters/store/migrations/003_rls.up.sql
new file mode 100644
index 0000000..6135fc6
--- /dev/null
+++ b/internal/adapters/store/migrations/003_rls.up.sql
@@ -0,0 +1,68 @@
+-- Migration 003: enforce per-user isolation at the DB layer via row-level
+-- security (ADR-012, data-model.md "Isolation invariant"). Stage 1 ships
+-- multi-user WITH this enforcement; it is the proof that user A cannot read or
+-- write user B's rows even if application-level WHERE clauses are wrong.
+--
+-- How it works:
+--   * Every policy keys off the per-request GUC tapir.current_user_id, set by the
+--     store's withUser helper via set_config('tapir.current_user_id', $1, true)
+--     (transaction-local — auto-reset on commit/rollback, never leaks across a
+--     pooled connection's requests).
+--   * current_setting('tapir.current_user_id', true) uses missing_ok = true: an
+--     UNSET GUC yields NULL, so the predicate is NULL → no rows match → deny-all.
+--     That is the safe default and is asserted in rls_test.go.
+--   * FORCE ROW LEVEL SECURITY: the app connects as the table OWNER (tapir), and
+--     owners BYPASS RLS unless forced. Without FORCE the policies below are dead
+--     for the production user. FORCE makes the owner subject to them. (A superuser
+--     DSN still bypasses RLS regardless — the test connects as a non-superuser,
+--     non-BYPASSRLS role so the enforcement is real, not theatre.)
+
+-- users: the row's own id IS the user_id for this table.
+ALTER TABLE users ENABLE ROW LEVEL SECURITY;
+ALTER TABLE users FORCE ROW LEVEL SECURITY;
+CREATE POLICY users_isolation ON users
+    FOR ALL
+    USING (id = current_setting('tapir.current_user_id', true)::uuid);
+
+ALTER TABLE videos ENABLE ROW LEVEL SECURITY;
+ALTER TABLE videos FORCE ROW LEVEL SECURITY;
+CREATE POLICY videos_isolation ON videos
+    FOR ALL
+    USING (user_id = current_setting('tapir.current_user_id', true)::uuid);
+
+ALTER TABLE transcripts ENABLE ROW LEVEL SECURITY;
+ALTER TABLE transcripts FORCE ROW LEVEL SECURITY;
+CREATE POLICY transcripts_isolation ON transcripts
+    FOR ALL
+    USING (user_id = current_setting('tapir.current_user_id', true)::uuid);
+
+ALTER TABLE summaries ENABLE ROW LEVEL SECURITY;
+ALTER TABLE summaries FORCE ROW LEVEL SECURITY;
+CREATE POLICY summaries_isolation ON summaries
+    FOR ALL
+    USING (user_id = current_setting('tapir.current_user_id', true)::uuid);
+
+ALTER TABLE summary_actions ENABLE ROW LEVEL SECURITY;
+ALTER TABLE summary_actions FORCE ROW LEVEL SECURITY;
+CREATE POLICY summary_actions_isolation ON summary_actions
+    FOR ALL
+    USING (user_id = current_setting('tapir.current_user_id', true)::uuid);
+
+-- sink_deliveries has NO user_id of its own; ownership is derived from the
+-- summary it belongs to. We key the policy directly off the GUC via EXISTS
+-- (rather than `summary_id IN (SELECT id FROM summaries)`) so it is self-contained
+-- and does not silently depend on summaries' own RLS being applied to the
+-- subquery. The WITH CHECK clause (defaulting to USING under FOR ALL) means a
+-- delivery row can only be inserted/updated when its summary is owned by the
+-- current user.
+ALTER TABLE sink_deliveries ENABLE ROW LEVEL SECURITY;
+ALTER TABLE sink_deliveries FORCE ROW LEVEL SECURITY;
+CREATE POLICY sink_deliveries_isolation ON sink_deliveries
+    FOR ALL
+    USING (
+        EXISTS (
+            SELECT 1 FROM summaries s
+             WHERE s.id = sink_deliveries.summary_id
+               AND s.user_id = current_setting('tapir.current_user_id', true)::uuid
+        )
+    );