fix(client): thread onresumptiontoken and onRequestStreamEnd through the send() resume path

[lntutor]

What's broken

When send() is called with a resumptionToken (the documented flow for resuming a long-running request after a disconnect), the resume branch reopens the SSE stream with the correct Last-Event-ID — but forwards neither onresumptiontoken nor onRequestStreamEnd to _startOrAuthSse():

if (resumptionToken) {
    this._startOrAuthSse({
        resumptionToken,
        replayMessageId: isJSONRPCRequest(message) ? message.id : undefined,
        requestSignal: options?.requestSignal   // threaded — but the two callbacks in the same options object are not
    }).catch(error => this.onerror?.(error));
    return;
}

Both callbacks arrive in the same options object (Protocol forwards { resumptionToken, onresumptiontoken, requestSignal } on every transport.send), and the original POST path threads both (_send, further down), as does resumeStream() for the identical stream. The comment above the resume branch shows requestSignal was threaded deliberately; the two callbacks sitting next to it were overlooked.

Observable failure

For the rest of a resumed request's life — including all of its internal reconnects, which rebuild options from StartSSEOptions — the caller's onresumptiontoken never fires again. The host's persisted token goes permanently stale, so a later resume replays already-delivered events (duplicate responses/side effects) or falls outside the server event store's retention window entirely. onRequestStreamEnd is dropped on the same line, so a resumed per-request stream that dies non-resumably never notifies the caller.

Related but distinct from #2499 / #2509: that fix seeds _handleSseStream's internal lastEventId tracker from the token; this one is about the caller-facing callbacks never being attached on the send() resume path at all. Even with #2509 merged, the callback still never fires here.

Fix

Thread onresumptiontoken and onRequestStreamEnd through the resume branch's _startOrAuthSse() call, matching the POST path and resumeStream().

Tests

New test in packages/client/test/client/streamableHttp.test.ts: resumes via send(..., { resumptionToken, onresumptiontoken, onRequestStreamEnd }) against a mocked GET SSE stream that delivers one id-bearing event and ends non-resumably (maxRetries: 0). Before the fix the GET goes out with the right Last-Event-ID but neither callback ever fires; after the fix both do. Full @modelcontextprotocol/client suite passes (749 tests), typecheck and lint clean. Changeset included (patch).

🤖 Generated with Claude Code

https://claude.ai/code/session_01N6RtoHuxrDqTUo9Mw9h4Cv

[changeset-bot]

🦋 Changeset detected

Latest commit: 713c448

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

This PR includes changesets to release 6 packages

Name	Type
@modelcontextprotocol/client	Patch
@modelcontextprotocol/core	Patch
@modelcontextprotocol/server	Patch
@modelcontextprotocol/server-legacy	Patch
@modelcontextprotocol/codemod	Patch
@modelcontextprotocol/core-internal	Patch

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