db: NullPool + WAL + busy_timeout — fixes QueuePool exhaustion under federation+classify load

src/psyc/db.py

@@ -17,11 +17,13 @@ from sqlalchemy import (
     Table,
     Text,
     create_engine,
+    event,
     func,
     insert,
     select,
 )
 from sqlalchemy.dialects.sqlite import insert as sqlite_insert
+from sqlalchemy.pool import NullPool
 
 from psyc import DATA_DIR, log
 from psyc.models import Case
@@ -209,10 +211,31 @@ _engine: Optional[Engine] = None
 
 
 def engine(db_path: Path = DB_PATH) -> Engine:
+    """Lazy-init the SQLite engine.
+
+    Uses NullPool — SQLite doesn't benefit from connection pooling (it's a
+    file, opens are cheap) and the default QueuePool starved the classify +
+    federation + cockpit-request workers under real load. WAL journal mode
+    + a 30s busy timeout let readers and a writer share the file safely.
+    """
     global _engine
     if _engine is None:
         db_path.parent.mkdir(parents=True, exist_ok=True)
-        _engine = create_engine(f"sqlite:///{db_path}", future=True)
+        _engine = create_engine(
+            f"sqlite:///{db_path}",
+            future=True,
+            poolclass=NullPool,
+            connect_args={"check_same_thread": False, "timeout": 30},
+        )
+
+        @event.listens_for(_engine, "connect")
+        def _sqlite_pragmas(dbapi_conn, _connection_record):  # noqa: D401
+            cur = dbapi_conn.cursor()
+            cur.execute("PRAGMA journal_mode=WAL")
+            cur.execute("PRAGMA synchronous=NORMAL")
+            cur.execute("PRAGMA busy_timeout=30000")
+            cur.close()
+
     return _engine