fix(protocol): add RequestAborted error code for AbortSignal cancellation

[sakthiveltofficial]

Aborting a request via AbortSignal produced SdkError with code
REQUEST_TIMEOUT — the same code as a genuine timeout — making it
impossible for callers to distinguish a deliberate cancellation from a
real timeout expiry.

Motivation and Context

The cancel() closure inside Protocol._requestWithSchema() wrapped
any non-SdkError abort reason unconditionally as
SdkErrorCode.RequestTimeout. When a caller does:

controller.abort(new DOMException('User cancelled', 'AbortError'));

the DOMException is not an SdkError, so it fell straight into that
generic fallback. The result was that user-initiated cancellations and
real timeouts were indistinguishable:

// Before this fix — fires on BOTH timeout AND manual abort
if (error.code === SdkErrorCode.RequestTimeout) {
  showRetryMessage(); // incorrectly shown on user cancellation too
}

Fixes #2165

How Has This Been Tested?

• Added a unit test in
  packages/core/test/shared/protocol.test.ts:
  • Sends a request with a 60 s timeout (well beyond the test duration)
  • Aborts immediately via controller.abort(new DOMException('User cancelled', 'AbortError'))
  • Asserts error.code === SdkErrorCode.RequestAborted
  • Asserts error.code !== SdkErrorCode.RequestTimeout
• Existing timeout test (timeout: 0) continues to assert
  RequestTimeout, confirming the timeout path is unaffected.
• Full test suite run: 553 tests passed, 0 failed

  pnpm --filter @modelcontextprotocol/core test
  

Breaking Changes

None. RequestAborted is a new enum member. No existing code
checks for it, and the timeout path (SdkErrorCode.RequestTimeout)
is completely unchanged — the timeout handler already passes a typed
SdkError(RequestTimeout, …) which hits the instanceof SdkError
branch and is passed through unmodified.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

Files changed (3, minimal diff):

packages/core/src/errors/sdkErrors.ts — added one enum member:

/** Request was aborted via AbortSignal */
RequestAborted = 'REQUEST_ABORTED',

packages/core/src/shared/protocol.ts — updated cancel() closure
to distinguish three cases instead of one:

// before
const error = reason instanceof SdkError
  ? reason
  : new SdkError(SdkErrorCode.RequestTimeout, String(reason));

// after
let error: SdkError;
if (reason instanceof SdkError) {
  error = reason;                                          // timeout path unchanged
} else if (reason instanceof DOMException && reason.name === 'AbortError') {
  error = new SdkError(SdkErrorCode.RequestAborted, reason.message);
} else {
  error = new SdkError(SdkErrorCode.RequestAborted, String(reason));
}

packages/core/test/shared/protocol.test.ts — one new test covering
the abort path.

[changeset-bot]

⚠️ No Changeset found

Latest commit: 667b4bc

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

Click here to learn what changesets are, and how to add one.

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

[pkg-pr-new]

Open in StackBlitz

@modelcontextprotocol/client

npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/client@2177

@modelcontextprotocol/codemod

npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/codemod@2177

@modelcontextprotocol/server

npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/server@2177

@modelcontextprotocol/express

npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/express@2177

@modelcontextprotocol/fastify

npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/fastify@2177

@modelcontextprotocol/hono

npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/hono@2177

@modelcontextprotocol/node

npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/node@2177

commit: 667b4bc