fix: return HTTP 404 for METHOD_NOT_FOUND in stateless transport (#1072) - #1078
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fix: return HTTP 404 for METHOD_NOT_FOUND in stateless transport (#1072)#1078elang2 wants to merge 1 commit into
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…elcontextprotocol#1072) The HttpServletStatelessServerTransport was returning HTTP 200 for all JSON-RPC responses, including METHOD_NOT_FOUND errors. Per the MCP Streamable HTTP specification (2026-07-28), an unrecognized method must return HTTP 404 with JSON-RPC error code -32601, not HTTP 500 or 200. This caused OpenAI's hosted MCP client to receive HTTP 500 (or 200 with an error body it could not process) when sending server/discover requests, resulting in HTTP 424 external_connector_error from the Responses API. The fix maps METHOD_NOT_FOUND (-32601) responses to HTTP 404 at the transport layer. All other JSON-RPC errors continue to use HTTP 200 per standard JSON-RPC conventions.
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Summary
HttpServletStatelessServerTransportserver/discovermapJsonRpcErrorToHttpStatus()helper — extensible for future error-to-status mappingsTest plan
testMissingHandlerReturnsMethodNotFoundErrorto verify HTTP 404 statustestUnknownMethodReturnsHttp404WithMethodNotFoundErrorforserver/discoverspecificallyFixes #1072