fix: handle GraphRecursionError as a graceful answer, not a 500

agentstore/server.py

@@ -15,6 +15,7 @@
 from fastapi.middleware.cors import CORSMiddleware
 from fastapi.responses import FileResponse
 from langchain_core.messages import AIMessage, HumanMessage
+from langgraph.errors import GraphRecursionError
 from pydantic import BaseModel, Field
 
 from .config import get_settings
@@ -78,6 +79,13 @@ def health() -> dict[str, str]:
     return {"status": "ok"}
 
 
+RECURSION_LIMIT_MESSAGE = (
+    "This question needed more back-and-forth between specialists than we allow per "
+    "request. Try asking a narrower question, or split it into separate questions — "
+    "one per topic (sales, inventory, reviews, customer)."
+)
+
+
 @app.post("/api/chat", response_model=ChatResponse)
 def chat(req: ChatRequest) -> ChatResponse:
     start = time.perf_counter()
@@ -86,6 +94,17 @@ def chat(req: ChatRequest) -> ChatResponse:
             {"messages": [HumanMessage(content=req.query)]},
             config={"recursion_limit": RECURSION_LIMIT},
         )
+    except GraphRecursionError:
+        # Not a server error: the supervisor/worker loop hit its hop budget
+        # without reaching FINISH (e.g. a question spanning many domains, or
+        # the LLM bouncing indecisively between specialists). Surface it as a
+        # normal answer so the UI renders a helpful chat bubble instead of a
+        # red error toast with an internal LangGraph error message.
+        return ChatResponse(
+            answer=RECURSION_LIMIT_MESSAGE,
+            agent="supervisor",
+            latency_ms=int((time.perf_counter() - start) * 1000),
+        )
     except Exception as exc:  # noqa: BLE001 — bubble up as 500 with a short msg
         raise HTTPException(status_code=500, detail=f"graph error: {exc}") from exc
 

tests/test_server.py

@@ -9,6 +9,7 @@
 
 from fastapi.testclient import TestClient
 from langchain_core.messages import AIMessage
+from langgraph.errors import GraphRecursionError
 
 from agentstore.server import _allow_credentials_for, app
 
@@ -45,6 +46,26 @@ def test_chat_rejects_empty_query():
         assert r.status_code == 422
 
 
+def test_chat_handles_recursion_limit_gracefully():
+    """A supervisor/worker loop that never reaches FINISH within
+    RECURSION_LIMIT should surface as a normal answer, not an opaque 500."""
+
+    class _StubGraph:
+        def invoke(self, state, config=None):
+            raise GraphRecursionError(
+                "Recursion limit of 8 reached without hitting a stop condition."
+            )
+
+    with patch("agentstore.server.get_graph", return_value=_StubGraph()):
+        with TestClient(app) as client:
+            r = client.post("/api/chat", json={"query": "a very complex multi-domain question"})
+            assert r.status_code == 200
+            body = r.json()
+            assert body["agent"] == "supervisor"
+            assert "narrower" in body["answer"]
+            assert isinstance(body["latency_ms"], int)
+
+
 # ── CORS ─────────────────────────────────────────────────────────────────────
 #
 # Wildcard origin + allow_credentials=True is an unsafe combination: browsers