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_persist_terminal_fallback.py

@@ -0,0 +1,64 @@
+"""persist_assistant_text_if_turn_missing"""
+
+from __future__ import annotations
+
+import uuid
+from svc.persistence.sqlite_store import SqliteStore
+from runtime.chat.persist_terminal_fallback import persist_assistant_text_if_turn_missing
+
+
+def test_fallback_inserts_when_missing(tmp_path) -> None:
+    db = tmp_path / "t.sqlite"
+    store = SqliteStore(str(db))
+    t = store.create_tenant("T")
+    tid = str(t["id"])
+    store.create_user_account(
+        tenant_id=tid,
+        username="u",
+        display_name="U",
+        role="owner",
+        password_hash="x",
+        is_active=True,
+    )
+    uid = str(store.get_user_by_username(tenant_id=tid, username="u")["id"])
+    s = store.create_session_for_user(title="s", tenant_id=tid, user_id=uid)
+    sid = str(s.id)
+    tu = uuid.uuid4().hex
+    store.add_message(session_id=sid, role="user", content="hi", turn_uuid=tu, event_type="user_text")
+    assert persist_assistant_text_if_turn_missing(
+        store=store,
+        session_id=sid,
+        turn_uuid=tu,
+        final_text="fallback body",
+        log_prefix="test_fallback",
+    )
+    msgs = store.get_messages(sid, limit=20)
+    assert any(getattr(m, "role", "") == "assistant" and "fallback" in str(getattr(m, "content", "")) for m in msgs)
+
+
+def test_fallback_skips_when_present(tmp_path) -> None:
+    db = tmp_path / "u.sqlite"
+    store = SqliteStore(str(db))
+    t = store.create_tenant("T2")
+    tid = str(t["id"])
+    store.create_user_account(
+        tenant_id=tid,
+        username="u2",
+        display_name="U",
+        role="owner",
+        password_hash="x",
+        is_active=True,
+    )
+    uid = str(store.get_user_by_username(tenant_id=tid, username="u2")["id"])
+    s = store.create_session_for_user(title="s", tenant_id=tid, user_id=uid)
+    sid = str(s.id)
+    tu = uuid.uuid4().hex
+    store.add_message(session_id=sid, role="user", content="hi", turn_uuid=tu, event_type="user_text")
+    store.add_message(session_id=sid, role="assistant", content="already", turn_uuid=tu, event_type="assistant_text")
+    assert not persist_assistant_text_if_turn_missing(
+        store=store,
+        session_id=sid,
+        turn_uuid=tu,
+        final_text="would duplicate",
+        log_prefix="test_skip",
+    )