fix(vector): verify writer sequence privileges

.superpowers/sdd/pgvector-task-1-report.md

@@ -73,3 +73,23 @@ Fresh verification after the fix wave:
 - Expanded focused adapter/config suite: `56 passed`.
 - Full harness: `466 passed, 5 deselected`.
 - Changed-file Ruff lint/format and `git diff --check`: clean.
+
+## Sequence privilege health follow-up
+
+Writer health now resolves the real serial/identity sequence for the `id` column of every
+required collection using `pg_get_serial_sequence`. It requires `USAGE` on each resolved
+sequence, which is the privilege used by the adapter's implicit `nextval`; sequence `SELECT` is
+not required because no adapter operation reads sequence state.
+
+The Docker fixture includes a writer role with complete table/hash-column authority but no
+sequence grant. Its health is deterministically unhealthy and a new-key upsert fails. Granting
+only sequence `USAGE` makes health green and the same port upsert succeeds. Sequence discovery is
+guarded for partial schemas so a missing `id` column produces the existing sanitized schema
+diagnostic instead of a PostgreSQL error.
+
+Fresh verification for this follow-up:
+
+- Docker pgvector L0 after formatting: `17 passed`.
+- Expanded focused adapter/config/parity suite: `57 passed`.
+- Full harness: `467 passed, 5 deselected`.
+- Changed-file Ruff lint/format and `git diff --check`: clean.