[2026-07-28] Transport & observability headers/metadata

[chr-hertel]

Tracking issue for the MCP Spec 2026-07-28 release — Transport & observability milestone.

Additive, non-breaking changes that surface routing/observability hints at the transport layer.

SEPs covered

SEP	Title	Spec PR
SEP-2243	HTTP Standardization (Mcp-Method / Mcp-Name headers)	#2243
SEP-2549	TTL for List Results (ttlMs / cacheScope)	#2549
SEP-414	OpenTelemetry Trace Context Propagation	#414

Sub-issues

• [Server][Client][Transport] SEP-2243: Emit Mcp-Method and Mcp-Name HTTP headers #353 — SEP-2243: Emit Mcp-Method and Mcp-Name HTTP headers (server + client)
• [Server][Schema] SEP-2549: ttlMs and cacheScope on list/read results #354 — SEP-2549: ttlMs and cacheScope on list/read results
• [Server][Client][Protocol] SEP-414: W3C Trace Context propagation via _meta #355 — SEP-414: W3C Trace Context propagation via _meta (server + client)

Notes

• All three SEPs are merged.
• All three are additive — implementable independently of the Milestone A stateless overhaul, though SEP-2243 should be gated on the per-request protocol version introduced in SEP-2575 ([Server][Client] SEP-2575: Stateless protocol (per-request version, server/discover, messages/listen) #340).