Implement SEP-2567: Sessionless MCP via Explicit State Handles #2185

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1. felixweinberger

   added this to 2026-07-28 Spec Implementationon May 29, 2026
2. github-project-automation

   moved this to Todo in 2026-07-28 Spec Implementationon May 29, 2026
3. mattzcarey commented on May 29, 2026

   

   mattzcarey

   on May 29, 2026

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   Status — SEP-2567 (Sessionless MCP via Explicit State Handles)

   Track: A (core) — tangled with SEP-2575 (#2184); the spec page calls these "the only genuinely tangled group — one without the other is half a model." Ships together.
   Spec: seps/2567-sessionless-mcp.md · merged spec#2567 2026-05-07

   What's done

   • Nothing in main yet.
   • Closed exploration: feat(core): deprecate sessionId on base Transport/BaseContext; legacySessionId() helper (SEP-2567) #2060 (Transport.sessionId / BaseContext.sessionId → optional + @deprecated, legacySessionId(t) helper, LegacySessionTransport type). The "session is a transport-specific concern, not a base-protocol one" framing carries forward into the v2-stateless stack.

   Open PR stack (same as #2184, v2-stateless label)

   See #2184 for the full chain. Sessionless wire behavior is implemented across #2131 (StreamableHTTP) and #2132 (stdio + InMemory).

   Outstanding (acceptance criteria, summary)

   • Mcp-Session-Id header removed from base transport interface (kept on concrete SHTTP transport as legacy-only)
   • List endpoints (tools/list, resources/list, prompts/list) MUST NOT depend on per-connection or prior-call state
   • List results MUST NOT change as a side effect of other requests on the same connection
   • JSON-RPC id unique per outstanding request (not per session)
   • Server MUST NOT require same-connection reuse — two requests over two connections succeed identically
   • subscriptions/listen opt-in model with io.modelcontextprotocol/subscriptionId correlation
   • Server MUST NOT infer capabilities from prior requests (per-message _meta, see Implement SEP-2575: Make MCP Stateless #2184)
   • Roots fetched via MRTR ListRootsRequest, not push (overlap with Implement SEP-2322: Multi Round-Trip Requests #2187)
   • Cancellation semantics: HTTP SSE-stream close treated as cancel; stdio uses notifications/cancelled

   Test backlog

   • [DRAFT] test(e2e): 2026-06 spec backlog — SEP-2260 + SEP-2575/2567 as expected-fail stubs #2180 (DRAFT) — paired with 2575 in the e2e known-failure stub matrix.

   Cross-cutting

   SEP-2567 is what makes Track B's sessionless HTTP / subscriptions slice possible. Track B can build the transport-shape contract against the agreed seam before #2131/#2132 merge.

   Dupes

   #2182 is a duplicate of this issue — should be closed.
4. felixweinberger

   self-assigned this

   on May 29, 2026
5. felixweinberger

   moved this from Todo to In Progress in 2026-07-28 Spec Implementationon May 29, 2026
6. norika1207-lab commented on Jun 2, 2026

   

   norika1207-lab

   on Jun 2, 2026 · Hidden as spam

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7. felixweinberger

   moved this from In Progress to Done in 2026-07-28 Spec Implementationon Jun 24, 2026
8. felixweinberger

   closed this as completedby moving to Done in 2026-07-28 Spec Implementationon Jun 24, 2026