fix(core): keep resumption options off cancellation notifications

[LizunovSergey]

Fixes #2646.

Root cause

When a legacy-era request was aborted, Protocol reused the original request's full transport options for notifications/cancelled. If that request carried a resumptionToken, StreamableHTTPClientTransport interpreted the cancellation send as a resume operation, swallowed the notification, and opened a resumed GET instead of posting the cancellation.

Fix

• Keep relatedRequestId on the cancellation send so request correlation is preserved.
• Do not pass resumptionToken or onresumptiontoken to the cancellation notification.
• Add a regression test that records the transport options for the cancellation send.
• Add a patch changeset for @modelcontextprotocol/core.

Validation

• Regression test fails against the previous implementation and passes with this change.
• pnpm --filter @modelcontextprotocol/core-internal test: 69 files, 1,434 tests passed.
• Monorepo build passed via the pre-push hook.
• Monorepo typecheck passed via the pre-push hook.
• pnpm lint:all passed.
• Changeset status and formatting checks passed.

[changeset-bot]

🦋 Changeset detected

Latest commit: 3445994

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

This PR includes changesets to release 6 packages

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

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commit: 3445994