feat: add postgres user engine store

docs/contracts.md

@@ -256,3 +256,9 @@ into `StoreRecord` envelopes with deterministic keys and index metadata, while
 `domain_record_from_store_record` restores those payloads to domain objects.
 These payloads are durable state and may contain sensitive values, so they must
 not be emitted as diagnostics.
+
+`user_engine.adapters.postgres.PostgresUserEngineStore` is the optional
+Postgres implementation. It accepts a provider-owned DB-API or psycopg-like
+connection, applies the bootstrap SQL in `migrate`, and persists generic
+records, audit records, and pending outbox events without depending on a
+specific driver package.

docs/development.md

@@ -10,7 +10,7 @@ tested immediately in local and agent environments.
 
 ```text
 src/user_engine/
-  adapters/    local standalone adapters and deterministic test doubles
+  adapters/    local standalone adapters, Postgres adapter, and test doubles
   domain/      transport- and persistence-neutral domain schemas
   errors.py    typed service exceptions for callers and future transports
   migrations.py ordered durable-store migration manifest

docs/postgres-durable-store-consumer-requirements.md

@@ -301,9 +301,15 @@ values, profile values, prepared-account matches, and access-profile defaults.
 Adapters must avoid logging payloads and should use `record_counts` or other
 redacted diagnostics for observability.
 
+USER-WP-0018 adds `PostgresUserEngineStore`, a dependency-free adapter that
+accepts a provider-supplied DB-API or psycopg-like connection. It writes generic
+records through `StoreRecord`, keeps audit and outbox payloads in their
+dedicated bootstrap tables, applies the bootstrap SQL through `migrate`, and
+uses the shared conformance harness with a fake Postgres connection for local
+unit coverage.
+
 Likely future follow-up work should be:
 
-- Add a Postgres adapter behind the existing store boundary.
 - Add provider-backed conformance tests for locking, uniqueness races,
   migration readiness, outbox claiming, redacted diagnostics, and restore
   validation.