allow initialization after unsupported mcp discovery - #1458
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RhysSullivan merged 4 commits intoAug 28, 2026
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Only initialize can open a session, so the streamable-HTTP transport rejected every other pre-session method with HTTP 400 + -32000 Server not initialized. Clients read that 400 as a transport failure and dropped the connection, so a client opening with an optional server/discover probe never got to fall back to initialize; over `executor mcp` it closed the bridge outright. Pre-session dispatch now answers any method other than initialize with -32601 Method not found on a 200. Done in the shared host-mcp package and wired into both session-creating sites, so the CLI bridge needs no shim.
The guard intercepted any POST body whose method was not initialize. That answered 200 before the streamable-HTTP transport could run its own checks, so a POST with a wrong Content-Type or an incomplete Accept got a success instead of the transport 415/406, and a structurally invalid JSON-RPC message (a fractional id, a non-object params, an unknown top-level field) got -32601 instead of the transport parse error. It now fires only where -32601 is the whole story: a POST that clears the transport content negotiation and carries a valid JSON-RPC 2.0 request. Validity comes from the SDK isJSONRPCRequest predicate, the same one behind the transport JSONRPCMessageSchema.parse, so the two cannot drift. Tests cover the real caller paths: the in-memory session store and the local app handler both answer -32601 for a valid probe, and pass a notification, a malformed id, a wrong Content-Type, and an incomplete Accept to the transport.
This was referenced Aug 28, 2026
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fixes #1449
executor mcpforwardedserver/discoverto the local streamable http endpoint before a session existed. the endpoint returned-32000 Server not initialized, and the stdio bridge closed before clients could fall back toinitialize.the bridge now answers that one unsupported pre-initialize method with
-32601 Method not found. all other messages still pass through to the daemon, and requests after initialization are unchanged.the raw stdio integration test sends discovery, initializes on the same connection, lists
execute, and calls it successfully.validation
bun run format:checkbun run lintbun run typecheckbun run test