fix: support Studio file-based app loading (#4838)

* fix: support Studio file-based app loading

* docs: clarify Studio loader invariant

README.md

@@ -400,6 +400,8 @@ cannot restore server privileges or be discarded by the runtime's startup
 cleanup. Keep the backend dependencies synchronized with `uv sync`; this
 compatibility path requires the declared LangGraph runtime versions and logs a
 warning if the persisted-store contract no longer matches its expectations.
+The documented command uses LangGraph's file-based custom-app loader, which is
+also covered directly by DeerFlow's regression tests.
 
 For workflows that invoke `backend/langgraph.json` through LangGraph Studio or
 a direct LangGraph Server, DeerFlow consumes the authenticated identity

backend/README.md

@@ -298,6 +298,8 @@ reactivate server-only privileges or be discarded by runtime startup cleanup.
 Run `uv sync` after dependency changes; this compatibility path requires the
 declared LangGraph runtime versions and warns when the persisted-store contract
 does not match its expectations.
+The same file-based custom-app loading path used by this command is covered by
+the backend regression suite.
 
 ---
 

backend/app/gateway/AGENTS.md

@@ -23,12 +23,16 @@ genuine system assistant IDs from the CLI-provided graph registry, removes
 their persisted active/version rows so graph registration recreates them, and
 demotes every other legacy `created_by=system` marker in both active assistants
 and version history. This must happen before runtime 0.30.0 loads and purges
-system-marked rows; a user application lifespan is too late. An empty graph
+system-marked rows; a user application lifespan is too late. LangGraph executes
-registry or absent persistence file is a no-op, while persistence parse/write
+this file-backed custom app without first registering its module in
-errors fail startup closed. The harness requires in-memory runtime 0.30.0 or
+`sys.modules`; keep its annotations eager so dataclass processing remains
-newer, and a persisted store containing no expected registered assistant row
+compatible with that loader, and preserve the direct file-loader regression
-emits a drift warning so changes to LangGraph's internal persistence contract
+test. An empty graph registry or absent persistence file is a no-op, while
-are observable. Because current create/update writes and all legacy
+persistence parse/write errors fail startup closed. The harness requires
+in-memory runtime 0.30.0 or newer, and a persisted store containing no
+expected registered assistant row emits a drift warning so changes to
+LangGraph's internal persistence contract are observable. Because current
+create/update writes and all legacy
 versions are sanitized, ordinary owner-scoped assistant version selection
 remains enabled. Ordinary authenticated users retain owner-scoped assistant
 reads/searches.

backend/app/gateway/langgraph_studio.py

@@ -3,11 +3,11 @@
 ``langgraph dev`` imports this custom application before entering the locked
 in-memory runtime lifespan. That ordering is intentional: runtime 0.30.0 loads
 and purges persisted ``created_by=system`` assistants before graph registration
-and before a user application lifespan can run.
+and before a user application lifespan can run. Keep annotations eager in this
+module: LangGraph's file loader executes it without first registering the module
+in ``sys.modules``, which breaks dataclasses with postponed annotations.
 """
 
-from __future__ import annotations
-
 import json
 import logging
 import os

backend/tests/test_langgraph_studio_lifespan.py

@@ -2,8 +2,10 @@
 
 from __future__ import annotations
 
+import importlib.util
 import json
 import logging
+import sys
 from pathlib import Path
 from uuid import NAMESPACE_DNS, uuid4, uuid5
 
@@ -198,3 +200,20 @@ def test_langgraph_config_loads_the_pre_runtime_studio_app():
     config = json.loads((Path(__file__).resolve().parents[1] / "langgraph.json").read_text(encoding="utf-8"))
 
     assert config["http"]["app"].endswith("app/gateway/langgraph_studio.py:langgraph_app")
+
+
+def test_studio_app_supports_langgraph_file_loader():
+    """The CLI executes the custom app without first registering its module."""
+    module_path = Path(__file__).resolve().parents[1] / "app" / "gateway" / "langgraph_studio.py"
+    module_name = f"langgraph_studio_file_loader_{uuid4().hex}"
+    spec = importlib.util.spec_from_file_location(module_name, module_path)
+
+    assert spec is not None
+    assert spec.loader is not None
+    assert module_name not in sys.modules
+
+    module = importlib.util.module_from_spec(spec)
+    spec.loader.exec_module(module)
+
+    assert module_name not in sys.modules
+    assert module.langgraph_app is not None