fix: harden assistant SQLite/PostgreSQL dual-backend (singleton, timeouts, warnings)

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

svc/config/database.py

@@ -3,6 +3,9 @@
 from __future__ import annotations
 
 import os
+import warnings
+
+_PG_URL_IGNORED_WARNED = False
 
 
 def assistant_db_backend() -> str:
@@ -22,8 +25,31 @@ def assistant_db_backend() -> str:
     )
 
 
+def _warn_if_postgres_url_ignored_for_sqlite() -> None:
+    """Emit once if PostgreSQL DSN env vars are set but backend is still SQLite."""
+    global _PG_URL_IGNORED_WARNED
+    if _PG_URL_IGNORED_WARNED or assistant_db_backend() != "sqlite":
+        return
+    for var in (
+        "AIA_ASSISTANT_DATABASE_URL",
+        "OPS_ASSISTANT_DATABASE_URL",
+        "AIA_ASSISTANT_PG_DSN",
+        "OPS_ASSISTANT_PG_DSN",
+    ):
+        if str(os.getenv(var) or "").strip():
+            _PG_URL_IGNORED_WARNED = True
+            warnings.warn(
+                f"{var} is set but assistant DB backend is sqlite; the PostgreSQL URL is ignored. "
+                "Set AIA_ASSISTANT_DB_BACKEND=postgresql (or pg/postgres) to use PostgreSQL.",
+                UserWarning,
+                stacklevel=2,
+            )
+            return
+
+
 def assistant_sqlalchemy_url() -> str:
     """SQLAlchemy URL for the assistant store (sqlite or postgresql+psycopg)."""
+    _warn_if_postgres_url_ignored_for_sqlite()
     if assistant_db_backend() == "postgresql":
         raw = assistant_postgres_dsn()
         if raw.startswith("postgresql+") or raw.startswith("postgres+"):
@@ -54,4 +80,15 @@ def assistant_postgres_dsn() -> str:
     return url
 
 
-__all__ = ["assistant_db_backend", "assistant_postgres_dsn", "assistant_sqlalchemy_url"]
+def reset_assistant_db_config_warnings_for_tests() -> None:
+    """Reset one-shot warnings (pytest only)."""
+    global _PG_URL_IGNORED_WARNED
+    _PG_URL_IGNORED_WARNED = False
+
+
+__all__ = [
+    "assistant_db_backend",
+    "assistant_postgres_dsn",
+    "assistant_sqlalchemy_url",
+    "reset_assistant_db_config_warnings_for_tests",
+]