fix: align protocol version negotiation#855
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May 18, 2026
| cargo semver-checks \ | ||
| --package rmcp \ | ||
| --baseline-rev ${{ github.event.pull_request.base.sha }} \ | ||
| --release-type minor \ |
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Without this, the CI fails completely on any non-patch change. With it, release-plz still determines the actual version bump, but the CI gate now only catches major bumps with breaking regressions. Minor additions, like this deprecation, are allowed.
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Fixes #852
Motivation and Context
The Rust SDK always responds with
2024-11-05, no matter what protocol version the client requests in the initialize body. The cross-SDK comparison in spec issue modelcontextprotocol/modelcontextprotocol#2721 shows that Rust is one of only two SDKs that ignore the body.This PR fix the protocol negotiation logic so that the server echoes the client-requested version when it's known. Otherwise, it returns the server-configured
protocol_versionas a fallback (this is the value set bywith_protocol_version, which defaults toLATEST).How Has This Been Tested?
Add integration tests
Breaking Changes
None. The dead
UnsupportedProtocolVersionvariant is marked#[deprecated].Types of changes
Checklist
Additional context