test: give collection database URL one cleanup owner

tests/helpers/worker_runtime.py

@@ -60,11 +60,6 @@ def isolated_runtime(worker="main"):
                 path.mkdir(mode=0o700)
                 patcher.setenv(name, str(path))
             (root / "data" / "agent_workspace").mkdir(mode=0o700, exist_ok=True)
-            # SQLite's default in-memory pool gives each thread an empty DB
-            # and can evict the main connection as TestClient threads churn.
-            # A worker-owned file preserves the collection schema across real
-            # connections. Tests that write rows still own explicit fixtures.
-            patcher.setenv("DATABASE_URL", f"sqlite:///{root / 'collection.db'}")
             # Browser resolution falls back to our XDG runtime directory.
             patcher.delenv("AGENT_BROWSER_SOCKET_DIR", raising=False)
             tmp = root / "tmp"