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>

runtime/chat/persist_terminal_fallback.py

@@ -0,0 +1,46 @@
+"""When the model run produced visible text but no ``chat_message`` row for this ``turn_uuid``."""
+
+from __future__ import annotations
+
+import logging
+from typing import Any
+
+_LOG = logging.getLogger(__name__)
+
+
+def persist_assistant_text_if_turn_missing(
+    *,
+    store: Any,
+    session_id: str,
+    turn_uuid: str,
+    final_text: str,
+    log_prefix: str,
+) -> bool:
+    """Insert one ``assistant_text`` row if none exists for ``turn_uuid``. Return True if inserted."""
+    tu = str(turn_uuid or "").strip()
+    body = str(final_text or "").strip()
+    if not tu or not body:
+        return False
+    try:
+        rows = store.get_messages(session_id=str(session_id), limit=400)
+        if any(
+            str(getattr(m, "role", "") or "").lower() == "assistant"
+            and str(getattr(m, "turn_uuid", "") or "").strip() == tu
+            for m in (rows or [])
+        ):
+            return False
+        store.add_message(
+            session_id=str(session_id),
+            role="assistant",
+            content=body,
+            turn_uuid=tu,
+            event_type="assistant_text",
+        )
+        _LOG.warning("%s session_id=%s turn_uuid=%s chars=%d", log_prefix, str(session_id), tu, len(body))
+        return True
+    except Exception:
+        _LOG.exception("%s_failed session_id=%s turn_uuid=%s", log_prefix, str(session_id), tu)
+        return False
+
+
+__all__ = ["persist_assistant_text_if_turn_missing"]