fix: reinitialize expired streamable sessions

[he-yufeng]

Summary

Fixes #1476.

When a Streamable HTTP server restarts, a client can keep sending POST requests with a stale MCP-Session-Id. The SDK currently reports the server's 404 response as ClientHttpNotImplemented and leaves the expired session in place.

This change handles a 404 from a request that used a session ID as an expired-session signal:

• clear the cached session ID
• let Client run a fresh initialize handshake on the same transport
• retry the original message once with the new session ID

The retry is limited to one attempt so repeated 404s still surface as errors instead of looping.

To verify

• pnpm --filter @modelcontextprotocol/client exec vitest run test/client/streamableHttp.test.ts -t "reinitializes and retries once"
• pnpm --filter @modelcontextprotocol/client exec vitest run test/client/streamableHttp.test.ts
• pnpm --filter @modelcontextprotocol/client typecheck
• pnpm --filter @modelcontextprotocol/client lint
• git diff --check
• pre-push hook: full workspace typecheck, build, and lint

[changeset-bot]

🦋 Changeset detected

Latest commit: 0c15f0c

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@modelcontextprotocol/client	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[pkg-pr-new]

Open in StackBlitz

@modelcontextprotocol/client

npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/client@2150

@modelcontextprotocol/codemod

npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/codemod@2150

@modelcontextprotocol/server

npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/server@2150

@modelcontextprotocol/server-legacy

npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/server-legacy@2150

@modelcontextprotocol/express

npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/express@2150

@modelcontextprotocol/fastify

npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/fastify@2150

@modelcontextprotocol/hono

npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/hono@2150

@modelcontextprotocol/node

npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/node@2150

commit: 0c15f0c

[he-yufeng]

Added a patch changeset for @modelcontextprotocol/client. Local validation: pnpm exec changeset status --since upstream/main shows the client patch bump, git diff --check passed, and the pre-push hook completed typecheck, build, and lint successfully.

[he-yufeng]

Rebased on current main and force-pushed the branch.

Validated locally:

• pnpm changeset status --since origin/main (@modelcontextprotocol/client patch)
• pnpm --filter @modelcontextprotocol/client typecheck
• pnpm --filter @modelcontextprotocol/client lint
• pnpm --filter @modelcontextprotocol/client exec vitest run test/client/streamableHttp.test.ts (54 passed)
• git diff --check origin/main..HEAD

The pre-push hook also completed the repo-wide build, typecheck, and lint steps successfully.

[he-yufeng]

Updated the branch to include the e2e expectation changes for session-expiry recovery.

The red e2e job was from two stale expectations:

• client-transport:http:session-404-reinitialize was still marked as a known failure even though this PR implements that behavior.
• client-transport:http:404-surfaces now explicitly covers the no-recovery-hook fallback path, so the transport still surfaces a 404 when no session recovery callback is installed.

Validation:

pnpm --filter @modelcontextprotocol/client exec vitest run test/client/streamableHttp.test.ts
# 54 passed
pnpm --filter @modelcontextprotocol/test-e2e test -- scenarios/transport-http.test.ts
# 24 passed, 1 expected fail
pnpm --filter @modelcontextprotocol/client typecheck
pnpm --filter @modelcontextprotocol/client lint
pnpm --filter @modelcontextprotocol/client build
pnpm --filter @modelcontextprotocol/test-e2e typecheck
pnpm --filter @modelcontextprotocol/test-e2e lint
git diff --check origin/main..HEAD

The pre-push hook also completed full repo typecheck, build, and lint before the force-push.