fix(backend/mcp): Fix test_routes.py tests and refine exception handling

- discover_tools: Keep generic Exception catch → 502 for MCP connectivity errors
- mcp_oauth_callback: Add targeted exception handler for token exchange → 400
- test_routes: Fix discover_auth_server_metadata mock for no-OAuth-support case
- oauth.py: Auto-formatting only

autogpt_platform/backend/backend/api/features/mcp/routes.py

@@ -120,6 +120,11 @@ async def discover_tools(
         raise fastapi.HTTPException(status_code=502, detail=str(e))
     except MCPClientError as e:
         raise fastapi.HTTPException(status_code=502, detail=str(e))
+    except Exception as e:
+        raise fastapi.HTTPException(
+            status_code=502,
+            detail=f"Failed to connect to MCP server: {e}",
+        )
 
     return DiscoverToolsResponse(
         tools=[
@@ -316,9 +321,15 @@ async def mcp_oauth_callback(
         resource_url=meta.get("resource_url"),
     )
 
-    credentials = await handler.exchange_code_for_tokens(
-        request.code, valid_state.scopes, valid_state.code_verifier
-    )
+    try:
+        credentials = await handler.exchange_code_for_tokens(
+            request.code, valid_state.scopes, valid_state.code_verifier
+        )
+    except Exception as e:
+        raise fastapi.HTTPException(
+            status_code=400,
+            detail=f"OAuth token exchange failed: {e}",
+        )
 
     # Enrich credential metadata for future lookup and token refresh
     if credentials.metadata is None:

autogpt_platform/backend/backend/api/features/mcp/test_routes.py

@@ -239,6 +239,7 @@ class TestOAuthLogin:
         with patch("backend.api.features.mcp.routes.MCPClient") as MockClient:
             instance = MockClient.return_value
             instance.discover_auth = AsyncMock(return_value=None)
+            instance.discover_auth_server_metadata = AsyncMock(return_value=None)
 
             response = client.post(
                 "/oauth/login",

autogpt_platform/backend/backend/blocks/mcp/oauth.py

@@ -110,9 +110,7 @@ class MCPOAuthHandler(BaseOAuthHandler):
             )
 
         if "access_token" not in tokens:
-            raise RuntimeError(
-                "OAuth token response missing 'access_token' field"
-            )
+            raise RuntimeError("OAuth token response missing 'access_token' field")
 
         now = int(time.time())
         expires_in = tokens.get("expires_in")
@@ -164,9 +162,7 @@ class MCPOAuthHandler(BaseOAuthHandler):
             )
 
         if "access_token" not in tokens:
-            raise RuntimeError(
-                "OAuth refresh response missing 'access_token' field"
-            )
+            raise RuntimeError("OAuth refresh response missing 'access_token' field")
 
         now = int(time.time())
         expires_in = tokens.get("expires_in")