René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Stateless mode drops HTTP responses for long-running tool calls","articleBody":"## Description\n\nWhen using `StreamableHTTPSessionManager` with `stateless=True` and `json_response=True`, HTTP responses for long-running tool calls (2-5+ minutes) are never sent back to the client. The client receives an empty response immediately while the server continues processing.\n\n## Environment\n\n- MCP SDK: 1.25.0\n- Python: 3.13\n- Client: Claude Code 2.1.9 (MCP protocol version `2025-11-25`)\n\n## Reproduction\n\n**Server configuration:**\n```python\nsession_manager = StreamableHTTPSessionManager(\n    app=mcp, \n    json_response=True, \n    stateless=True\n)\n```\n\n**Tool that takes several minutes:**\n```python\n@mcp.call_tool()\nasync def call_tool(name: str, arguments: dict):\n    result = await long_running_operation()  # 2-5 minutes\n    return result\n```\n\n**Steps:**\n1. Connect Claude Code to the MCP server\n2. Call the long-running tool\n3. Client receives empty response immediately\n4. Server logs show tool completed successfully with valid result\n\n## Expected Behavior\n\nHTTP response should be sent after tool completes, containing the result.\n\n## Actual Behavior\n\n- Client receives empty response immediately\n- Server processes tool call successfully\n- Server generates result (logged correctly)\n- **HTTP response is never sent to client**\n\n## Log Evidence\n\n```\n12:01:55.130 - Client POST request received (mcp_protocol: 2025-11-25)\n12:01:56.080 - tool_call event logged\n12:06:50.269 - Tool result generated:\n               content_count: 1, content_types: [\"text\"]\n               ❌ NO HTTP response logged for client request\n```\n\nKey observation: Only ONE `mcp_request` logged but both `tools/list` and `tools/call` execute. Response routing appears broken for the second request.\n\n## Workaround Attempted\n\nSetting `stateless=False` causes `400 Bad Request: Missing session ID` - incompatible with Claude Code's connection pattern.\n\n## Hypothesis\n\nIn `_handle_stateless_request`, when rapid successive requests arrive from the same client, response routing fails for long-running operations. The response is generated but never correlated back to the correct HTTP connection.","author":{"url":"https://github.com/tony-nekola-silk","@type":"Person","name":"tony-nekola-silk"},"datePublished":"2026-01-16T13:35:16.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":0},"url":"https://github.com/1886/python-sdk/issues/1886"}