fix(langgraph): lazy-load FastAPI endpoint import

integrations/langgraph/python/ag_ui_langgraph/__init__.py

@@ -17,7 +17,6 @@
     LangGraphReasoning,
 )
 from .utils import json_safe_stringify, make_json_safe
-from .endpoint import add_langgraph_fastapi_endpoint
 from .middlewares.state_streaming import StateStreamingMiddleware, StateItem
 from .a2ui_tool import (
     get_a2ui_tools,
@@ -27,6 +26,10 @@
     BASIC_CATALOG_ID,
 )
 
+# FastAPI is an optional extra. Keep the endpoint import lazy so middleware-only
+# installs (`pip install ag-ui-langgraph` without `[fastapi]`) can still import
+# LangGraphAgent and helpers without requiring fastapi (#2013).
+
 __all__ = [
     "LangGraphAgent",
     "get_a2ui_tools",
@@ -53,5 +56,13 @@
     "StateStreamingMiddleware",
     "StateItem",
     "json_safe_stringify",
-    "make_json_safe"
+    "make_json_safe",
 ]
+
+
+def __getattr__(name: str):
+    if name == "add_langgraph_fastapi_endpoint":
+        from .endpoint import add_langgraph_fastapi_endpoint
+
+        return add_langgraph_fastapi_endpoint
+    raise AttributeError(f"module {__name__!r} has no attribute {name!r}")

integrations/langgraph/python/tests/test_lazy_fastapi_import.py

@@ -0,0 +1,44 @@
+"""Regression for #2013 — package import must not require fastapi.
+
+`fastapi` is an optional extra, but `__init__.py` used to eagerly import
+`endpoint.py`, which imports fastapi at module top. Middleware-only installs
+then failed on any `import ag_ui_langgraph`.
+"""
+
+from __future__ import annotations
+
+import importlib
+import sys
+import unittest
+
+
+class TestLazyFastapiImport(unittest.TestCase):
+    def test_init_does_not_import_endpoint_module(self):
+        # Drop package modules so we re-import against current source.
+        for name in list(sys.modules):
+            if name == "ag_ui_langgraph" or name.startswith("ag_ui_langgraph."):
+                del sys.modules[name]
+
+        import ag_ui_langgraph  # noqa: F401
+
+        self.assertNotIn("ag_ui_langgraph.endpoint", sys.modules)
+
+        # Core exports still resolve without touching the FastAPI path.
+        from ag_ui_langgraph import LangGraphAgent  # noqa: F401
+
+        self.assertNotIn("ag_ui_langgraph.endpoint", sys.modules)
+
+    def test_endpoint_export_is_available_lazily(self):
+        for name in list(sys.modules):
+            if name == "ag_ui_langgraph" or name.startswith("ag_ui_langgraph."):
+                del sys.modules[name]
+
+        import ag_ui_langgraph
+
+        endpoint_fn = ag_ui_langgraph.add_langgraph_fastapi_endpoint
+        self.assertTrue(callable(endpoint_fn))
+        self.assertIn("ag_ui_langgraph.endpoint", sys.modules)
+
+
+if __name__ == "__main__":
+    unittest.main()