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fix(server): keep discover lifecycle bootstrap-neutral - #1248
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We hit this in production: Claude Code sometimes opens a stdio session with a bare |
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@faisal-shah Since a user is hitting this in production, I went ahead and pushed the review fixes. @tenequm We'll include this fix in the next release. |
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…lure (#218) A client that probes `server/discover` before `initialize` (e.g. Claude Code) permanently latched rmcp's internal `request_metadata_required` flag on the session, even after falling back to the classic (`initialize`-negotiated) lifecycle. Every later request without per-request `_meta` -- including an ordinary `tools/list` -- was then rejected with -32602, so the client loaded zero tools. Upstream fix: modelcontextprotocol/rust-sdk#1248, shipped in rmcp 3.5.1. Adds a stdio regression test driving the exact discover -> initialize -> notifications/initialized -> tools/list sequence over an in-memory duplex transport; it reproduces the -32602 failure against the prior rmcp 3.5.0 pin and passes against 3.5.1. Closes #217 Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>
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Summary: Claude Code can time out a discovery probe and fall back to legacy initialization. In `rmcp` 3.5.0 the probe latches modern request-metadata validation, so subsequent legacy catalog requests fail and Claude exposes no tools. Import official `rmcp` and `rmcp-macros` 3.5.1 through Reindeer, including upstream PR #1248: modelcontextprotocol/rust-sdk#1248. Discovery remains neutral until initialization or a valid non-discovery request selects the lifecycle. The SDK also supplies missing modern catalog/resource cache hints centrally, allowing downstream duplicate cache-hint handlers to be removed. Legacy proxy result completion and application-specific subscription/socket fixes remain separate. Only `rmcp` and `rmcp-macros` change versions in `Cargo.lock`; no transitive dependency versions change. Vendored sources match the official crate checksums. Update Symphony startup assertions for the SDK-provided modern cache fields in the same import, and repair documentation links to the renamed vendored sources. Reviewed By: dtolnay Differential Revision: D124891804 fbshipit-source-id: bfc1183f0d8f37b37660684fb7ab4ec2ea6380ba
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…350) ## What broke Claude Code intermittently showed pond as `connected - tools fetch failed`, with no tools and no resources: ``` request _meta is missing or has malformed required fields: io.modelcontextprotocol/protocolVersion, io.modelcontextprotocol/clientCapabilities ``` Claude Code opens a stdio server with a `server/discover` probe. `pond mcp` opens the store before it reads stdin, so on a slow open (3.3 s here, against 1.4-2.2 s on the good starts) the probe reply misses Claude Code's wait and it falls back to a classic `initialize`. Both requests then reach pond. On rmcp 3.5.0 the discover probe committed the connection to the 2026-07-28 inline lifecycle, so pond answered `initialize` at 2025-11-25 and then rejected the classic `tools/list` and `resources/list` that followed, for lacking 2026-07-28 `_meta`. Claude Code's MCP log shows the sequence: ``` Connection established ... "protocolEra":"legacy","negotiatedProtocolVersion":"2025-11-25" stdio server answered the server/discover probe after it had connected legacy ... Failed to fetch resources: request _meta is missing or has malformed required fields: ... Failed to fetch tools: request _meta is missing or has malformed required fields: ... ``` Reproduced on the released 0.19.6 two ways: a `claude -p` run against `pond mcp` behind a 4 s startup delay (no pond tools), and a script that writes discover, initialize, initialized and tools/list back to back (`tools/list` gets `-32602`). This is not the #334 failure: there the first request lacked `_meta`; here it is a complete discover probe. ## Fix - rmcp 3.5.0 -> 3.5.1. It ships [rust-sdk#1248](modelcontextprotocol/rust-sdk#1248), which keeps a discover probe from selecting a lifecycle, so a following `initialize` selects the classic one. The same change answers a malformed first request with `-32602` and keeps reading. - That second half is what `RecoverableOpener` (#334) did by hand, and its doc said to drop it once #1248 shipped, so it is removed. `serve_io` passes the plain transport again. ## Tests - New `discover_probe_then_initialize_serves_classic_requests`: discover, initialize, initialized and tools/list written back to back. `tools/list` must return tools. - `malformed_opener_leaves_initialize_fallback_open` is kept as the guard for what the wrapper covered, now against rmcp's own handling. Both tests share an `exchange` helper that writes raw frames and collects replies by id. ## Verified - `cargo test --lib transport::mcp::` (12 passed), `cargo clippy --all-targets -- -D warnings`, `cargo fmt --check`. - The back-to-back script against this build: `tools/list` returns the 4 tools (`-32602` on 0.19.6). - `claude -p` (Claude Code 2.1.296) against this build behind the same 4 s startup delay: all 4 pond tools present, and the MCP log reads "answered the server/discover probe after its bound, so it was only slow to start and speaks the new protocol". ## Release note `pond mcp` no longer loses its tools when Claude Code's discovery probe and its `initialize` fallback both reach a slow-starting server, which showed pond as connected with "tools fetch failed" until a manual reconnect. No action needed.
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Summary
server/discoverrequests bootstrap-neutralinitializeVerification
cargo test --package rmcp --features "client transport-io macros schemars"cargo clippy --package rmcp --features "client transport-io macros schemars" --lib --test test_server_initialization --test test_stateless_server_requests --test test_subscriptions -- -D warnings