fix(vector): provision per-field embedding storage via durable markers (least-privilege safe)

[pdlug]

Problem

On a least-privilege Postgres role (USAGE on public, full DML, but no CREATE), every runtime vector op failed with permission denied for schema public (SQLSTATE 42501). The cause: each vector op (upsertEmbedding / deleteEmbedding / vectorSearch / createVectorIndex) lazily ran CREATE TABLE IF NOT EXISTS for its per-(kind,field) table on the request connection — and Postgres runs the schema aclcheck before the IF NOT EXISTS short-circuit, so it failed even when the table already existed.

Fulltext already avoided this via the #135 durable-contribution machinery; the #161 vector cutover (v0.29) shipped an in-process-latch shortcut that bypassed it — exactly what the design doc said not to do.

Fix

Vectors now ride the same durable-marker machinery as fulltext:

• Boot (privileged): createStoreWithSchema provisions every embedding (kind,field) table + a durable marker; evolve() provisions fields it introduces.
• Runtime (DML-only): the hot path asserts the marker with a cached SELECT — never DDL. An un-provisioned slot throws StoreNotInitializedError (not a raw 42501). createVerifiedStore verifies vector markers at attach.
• reembedVectorField re-stamps the marker after recreating storage at a new dimension; vector-field reclaim clears it when it drops a table.
• The in-process vectorSlotLatch is removed; a shared resolveGraphVectorSlots enumerator is the single source of truth for boot materialization and runtime assertion.

Key files

• backend/drizzle/contribution-materializations.ts — generalized the materializer to any contribution set; added ensureVectorSlot / assertVectorSlot / dropVectorSlot (+ force, deleteMarker).
• backend/drizzle/{postgres,sqlite}.ts — marker-gated vector methods; shared materializer across tx-scoped backends.
• store/store.ts, schema/manager.ts, store/materialize-removals.ts, backend/migrate-vectors.ts, core/embedding.ts, errors/index.ts.

⚠️ Breaking change (minor)

Vector ops now require a prior privileged createStoreWithSchema — exactly as fulltext already does. A plain createStore + embedding write with no provisioning step throws StoreNotInitializedError instead of lazily creating the table.

Migration: run createStoreWithSchema(graph, adminBackend) once under the schema-owner role after upgrading. It creates the per-field tables + markers; least-privilege runtimes then assert markers (SELECT) and run vector DML with zero DDL — no GRANT CREATE needed. Changeset included.

Tests

• New postgres-vector-least-privilege.test.ts — the canonical regression: a USAGE-only role (no CREATE) runs vector upsert+search after the owner provisions, and gets StoreNotInitializedError (not 42501) when unprovisioned.
• Extended the cross-backend materializer unit tests; updated lazy-usage tests/examples/fixtures to provision via createStoreWithSchema.
• SQLite 3493 passed · Postgres + integration 914 passed · property 320 passed · typecheck + lint clean.

Docs updated (semantic-search, backend-setup, troubleshooting, architecture, graph-extensions, schema-evolution, schema-management) — the old "created lazily on first write" claims were the trap that led here.