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Harden the dual-era stream loop's era-lock and rejection semantics (#3040)

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Max 2026-07-01 17:07:12 +01:00 • committed by GitHub
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docs/migration.md
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@ -411,6 +411,8 @@ On the high-level `Client`, `client.server_capabilities`, `client.server_info`,
In v1, connecting to a server always performed the `initialize` handshake. In v2, `Client` defaults to `mode='auto'`: on enter it probes `server/discover` and, if the server doesn't support it, falls back to the `initialize` handshake. Pass `mode='legacy'` to force the initialize handshake and reproduce v1's byte-identical pre-2026 behavior, or pass a modern protocol-version string (e.g. `mode='2026-07-28'`) to pin a version without probing.
The probe is transport-independent: v2 servers answer it over stdio (and any other stream-pair transport) as well as streamable HTTP, so `mode='auto'` lands on `2026-07-28` against a v2 server on every transport. If your stdio workflow relies on server-initiated requests (sampling, push elicitation), pass `mode='legacy'` — a 2026-07-28 connection refuses them on every transport.
For an in-process `Client(server)` (where `server` is a `Server` or `MCPServer` instance), `mode='auto'` dispatches calls directly through `DirectDispatcher` with no JSON-RPC framing. Pass `mode='legacy'` if you need the in-memory JSON-RPC transport that v1 used.
`Client.send_ping()` is deprecated (ping is removed in 2026-07-28); pin `mode='legacy'` if you need it.