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>

svc/persistence/pg_adapter.py

@@ -0,0 +1,68 @@
+"""psycopg connection surface compatible with sqlite3 usage in SqliteStore."""
+
+from __future__ import annotations
+
+from typing import Any, Iterable, Sequence
+
+import psycopg
+from psycopg.rows import dict_row
+
+from svc.persistence.pg_compat import adapt_sql_for_postgres
+
+
+def normalize_psycopg_conninfo(url: str) -> str:
+    """Strip SQLAlchemy driver suffix so :func:`psycopg.connect` accepts the URI."""
+    u = str(url or "").strip()
+    for prefix in (
+        "postgresql+psycopg://",
+        "postgresql+psycopg2://",
+        "postgres+psycopg://",
+        "postgres+psycopg2://",
+    ):
+        if u.startswith(prefix):
+            rest = u.split("://", 1)[1]
+            return "postgresql://" + rest
+    return u
+
+
+class PgCursorShim:
+    def __init__(self, raw: Any) -> None:
+        self._raw = raw
+
+    def fetchone(self) -> Any:
+        return self._raw.fetchone()
+
+    def fetchall(self) -> list[Any]:
+        return self._raw.fetchall()
+
+    @property
+    def lastrowid(self) -> int:
+        return 0
+
+    @property
+    def rowcount(self) -> int:
+        return int(self._raw.rowcount or 0)
+
+    def __iter__(self) -> Iterable[Any]:
+        return iter(self._raw)
+
+
+class PgConnShim:
+    def __init__(self, raw: psycopg.Connection) -> None:
+        self._raw = raw
+
+    def execute(self, sql: str, params: Sequence[Any] | None = None) -> PgCursorShim:
+        adapted = adapt_sql_for_postgres(sql)
+        cur = self._raw.execute(adapted, params or ())
+        return PgCursorShim(cur)
+
+    def executemany(self, sql: str, seq_of_params: Sequence[Sequence[Any]]) -> None:
+        adapted = adapt_sql_for_postgres(sql)
+        self._raw.executemany(adapted, seq_of_params)
+
+
+def connect_postgres(url: str) -> psycopg.Connection:
+    return psycopg.connect(normalize_psycopg_conninfo(url), row_factory=dict_row)
+
+
+__all__ = ["PgConnShim", "PgCursorShim", "connect_postgres", "normalize_psycopg_conninfo"]