1823aae891Co-authored-by: Matt <77928207+mattzcarey@users.noreply.github.com> Co-authored-by: Konstantin Konstantinov <KKonstantinov@users.noreply.github.com> Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
1.4 KiB
| @modelcontextprotocol/client | @modelcontextprotocol/core-internal |
|---|---|
| minor | minor |
Add opt-in protocol version negotiation on ClientOptions.versionNegotiation. The default is unchanged: without the option (or with mode: 'legacy') the client performs today's 2025 connect sequence byte-identically. mode: 'auto' probes the server with server/discover at
connect time and conservatively falls back to the plain legacy initialize handshake on the same connection unless the outcome is definitive modern evidence (with a supported-versions list that has no 2025-era entry there is nothing to fall back to, and connect rejects
with a typed error instead); a network outage rejects with a typed connect error, and a probe timeout is transport-aware — on stdio it indicates
a legacy server and falls back to initialize on the same stream, on HTTP it rejects with a typed timeout error.
mode: { pin: '<version>' } negotiates exactly the pinned modern revision with no fallback. Probe policy lives under probe: { timeoutMs? } — the probe inherits the standard request timeout. The probe's MCP-Protocol-Version/Mcp-Method headers derive from the probe
message body; the transport version slot is never touched during negotiation, so legacy-era traffic carries zero 2026 headers by construction. Adds the SdkErrorCode.EraNegotiationFailed code for negotiation-phase connect failures.