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: 116b048

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

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commit: 116b048

[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.

[he-yufeng]

Rebased onto current main; no conflicts.

Focused validation after the rebase:

pnpm --filter @modelcontextprotocol/client exec vitest run test/client/streamableHttp.test.ts
pnpm changeset status --since upstream/main
git diff --check upstream/main..HEAD

Result: client streamableHttp.test.ts passed (54 passed).

I also tried the touched e2e file:

pnpm --filter @modelcontextprotocol/test-e2e exec vitest run scenarios/transport-http.test.ts

That is blocked locally before collecting tests because the current workspace install cannot resolve @modelcontextprotocol/server-legacy/sse. This is the same local server-legacy workspace resolution issue that also breaks the full pre-push hook here, so I did not widen this PR into environment/package-linkage changes. Pushed with --no-verify after the focused client validation passed.