Phase 2 of the MCP 2026-07-28 migration (#69931), on top of the SDK 2.x
migration (#88180):
- Protocol-era negotiation (_negotiate_session): per-server `protocol`
config key — auto (default, handshake-first with server/discover
fallback on -32022/-32601), stateless (discover-first), legacy
(handshake only). Auto is handshake-first deliberately: zero extra
round-trips and zero behavior change for the entire existing server
fleet, while 2026-07-28-only servers now connect via the fallback.
All four transport call sites (stdio, SSE, new HTTP, legacy HTTP)
route through the one choke point, so the CLI/desktop probe path
inherits it too.
- SEP-2549 list caching: tools/list ttlMs/cacheScope hints are captured
during discovery and bound to the lazy-startup schema cache — TTL'd
entries expire and force a live re-probe; hint-less (pre-2026)
servers keep the never-expires behavior. Pagination continuation now
speaks both SDK generations (params= vs cursor=).
- SEP-837: OAuth client metadata declares application_type=native
(config-overridable), with a fallback for 1.x-era metadata models.
(RFC 9207 iss validation and SEP-2352 issuer-keyed credentials are
native to SDK 2.0's OAuthClientProvider — verified, no client-side
gap.)
- SEP-2577 deprecation posture: SamplingHandler docstring marks the
Sampling feature as upstream-deprecated (12-month window) — kept
fully functional, closed to new capability.
- Docs: `protocol` key in the MCP config reference.
Teknium
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