feat(persistence): PostgreSQL assistant store, chat persist fixes, gateway scripts

- Add SQLAlchemy Core repos, pg adapter/compat, assistant_store factory, Alembic bootstrap and migration/cutover scripts.

- Harden chat_message writes (NUL scrub for PG), turn_uuid on attempt failure, WS turn_runner fallbacks and gateway executed_turn_uuid init.

- start_gateway: log paths, PS7 stderr handling via cmd, background stdout/stderr redirect; runtime assistant_runtime_log_dir export.

- Ops: clear_all_chat_sessions with PG-only --postgresql and env-gated wipe; clear_postgres_chat_sessions.ps1.

- Tests: SA repos, pg compat, persist fallback, smoke env isolation; CI and docs touch-ups.

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/test_sa_chat_messages.py

@@ -0,0 +1,91 @@
+"""SQLAlchemy slice tests: chat_message hot paths (phase-4 migration)."""
+
+from __future__ import annotations
+
+import json
+
+import pytest
+
+from svc.persistence.db.engine import clear_assistant_engine_cache
+from svc.persistence.sqlite_store import SqliteStore
+
+
+@pytest.fixture
+def fresh_sqlite_store(monkeypatch: pytest.MonkeyPatch, tmp_path):
+    monkeypatch.delenv("AIA_ASSISTANT_DB_BACKEND", raising=False)
+    monkeypatch.setenv("OPS_WORKSPACE_ROOT", str(tmp_path))
+    dbfile = tmp_path / "sa_msg.sqlite"
+    monkeypatch.setenv("AIA_ASSISTANT_DB_PATH", str(dbfile))
+    clear_assistant_engine_cache()
+    s = SqliteStore(str(dbfile))
+    try:
+        yield s
+    finally:
+        clear_assistant_engine_cache()
+
+
+def test_sa_chat_message_add_list_meta(fresh_sqlite_store: SqliteStore) -> None:
+    s = fresh_sqlite_store
+    sess = s.create_session("M")
+    m1 = s.add_message(sess.id, "user", "hello")
+    assert m1.id > 0
+    m2 = s.add_message(sess.id, "assistant", "hi")
+    assert m2.id > m1.id
+    meta = s.get_session_messages_meta(sess.id)
+    assert meta.session_id == sess.id
+    assert meta.message_count == 2
+    assert meta.last_message_id == m2.id
+    assert s.count_messages(sess.id) == 2
+    assert s.get_last_message_id(sess.id) == m2.id
+    rows = s.get_messages(sess.id, limit=10)
+    assert [x.role for x in rows] == ["user", "assistant"]
+    assert rows[0].content == "hello"
+    after = s.get_messages_after_id(session_id=sess.id, after_id=m1.id, limit=10)
+    assert len(after) == 1
+    assert after[0].id == m2.id
+
+
+def test_sa_chat_message_delete_refreshes_session_ts(fresh_sqlite_store: SqliteStore) -> None:
+    s = fresh_sqlite_store
+    sess = s.create_session("D")
+    a = s.add_message(sess.id, "user", "a", timestamp="2020-01-01T00:00:01+00:00")
+    b = s.add_message(sess.id, "user", "b", timestamp="2020-01-01T00:00:02+00:00")
+    assert s.get_session(sess.id).last_message_at is not None
+    assert s.delete_message(session_id=sess.id, message_id=b.id) is True
+    meta = s.get_session_messages_meta(sess.id)
+    assert meta.message_count == 1
+    assert meta.last_message_id == a.id
+    assert s.delete_message(session_id=sess.id, message_id=999999) is False
+
+
+def test_sa_chat_message_update_content(fresh_sqlite_store: SqliteStore) -> None:
+    s = fresh_sqlite_store
+    sess = s.create_session("U")
+    m = s.add_message(sess.id, "assistant", "old", event_payload={"k": 1})
+    ok = s.update_message_content(session_id=sess.id, message_id=m.id, content="new", event_payload={"k": 2})
+    assert ok is True
+    row = s.get_messages(sess.id, limit=5)[0]
+    assert row.content == "new"
+    assert json.loads(row.event_payload or "{}")["k"] == 2
+
+
+def test_sa_chat_message_scrubs_nul_byte(fresh_sqlite_store: SqliteStore) -> None:
+    s = fresh_sqlite_store
+    sess = s.create_session("N")
+    m = s.add_message(sess.id, "user", "a\x00b", event_payload={"x": "y\x00z"})
+    rows = s.get_messages(sess.id, limit=5)
+    assert rows[0].content == "ab"
+    ep = json.loads(rows[0].event_payload or "{}")
+    assert ep["x"] == "yz"
+
+
+def test_sa_chat_message_tool_window_prepend(fresh_sqlite_store: SqliteStore) -> None:
+    s = fresh_sqlite_store
+    sess = s.create_session("T")
+    asst = s.add_message(sess.id, "assistant", "call", tool_calls='{"x":1}')
+    tool_calls = json.dumps({"assistant_message_id": asst.id}, ensure_ascii=False)
+    s.add_message(sess.id, "tool", "result", tool_calls=tool_calls)
+    win = s.get_messages(sess.id, limit=1)
+    assert len(win) == 2
+    assert win[0].id == asst.id
+    assert win[1].role == "tool"