feat: expose HTTP status code and headers on SDK error classes

[corvid-agent]

Summary

• Adds optional statusCode and headers properties to all A2A SDK error classes (TaskNotFoundError, TaskNotCancelableError, PushNotificationNotSupportedError, UnsupportedOperationError, ContentTypeNotSupportedError, InvalidAgentResponseError, AuthenticatedExtendedCardNotConfiguredError) so that consumers can implement HTTP-aware error handling.
• Updates the REST transport (RestTransport) to extract HTTP status code and response headers from the Response object and pass them through when constructing error instances via mapToError.
• Exports the new A2AErrorHttpDetails interface from the client entry point for use by consumers.
• Adds comprehensive tests covering all error types, verifying that statusCode and headers are correctly populated on errors thrown by the REST transport.

Closes #317

Test plan

• All 414 existing tests pass (no regressions)
• New tests verify statusCode is set on TaskNotFoundError (404), TaskNotCancelableError (409), PushNotificationNotSupportedError (400), UnsupportedOperationError (405), ContentTypeNotSupportedError (415), InvalidAgentResponseError (502), and AuthenticatedExtendedCardNotConfiguredError (401)
• New test verifies that response headers (e.g. Retry-After, X-RateLimit-Remaining) are available on errors for rate-limiting / backoff strategies
• Backward compatibility verified: constructor changes are additive (second parameter is optional), so existing code including JSON-RPC error subclasses continues to work without modification
• TypeScript lint passes with no new errors

🤖 Generated with Claude Code

[gemini-code-assist]

Summary of Changes

Hello @corvid-agent, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly improves the error handling capabilities of the A2A SDK by exposing underlying HTTP details directly within SDK error classes. This change empowers developers to build more robust and responsive applications by enabling them to react to specific HTTP status codes and headers, such as implementing retry logic based on Retry-After headers, directly from caught SDK errors. The modifications are backward-compatible, ensuring existing integrations remain unaffected.

Highlights

• Enhanced Error Classes: SDK error classes now include optional statusCode and headers properties, enabling more granular HTTP-aware error handling for consumers.
• REST Transport Integration: The RestTransport has been updated to extract HTTP status codes and response headers from Response objects and populate these new properties on thrown errors.
• New Interface Export: The A2AErrorHttpDetails interface is now exported from the client entry point, allowing consumers to type and leverage the new error details.
• Comprehensive Testing: New tests confirm the correct population of statusCode and headers across all relevant error types and scenarios, including specific rate-limiting headers.

Changelog

• src/client/index.ts
  • Exports the new A2AErrorHttpDetails interface.
• src/client/transports/rest_transport.ts
  • Introduces a new static method extractHttpDetails to parse HTTP status code and headers from a Response object.
  • Modifies the _handleErrorResponse method to utilize extractHttpDetails and pass the extracted HTTP details to the mapToError function.
  • Updates the mapToError function to accept and forward the HTTP details to the constructors of various A2A error classes.
• src/errors.ts
  • Defines the A2AErrorHttpDetails interface, specifying statusCode and headers properties.
  • Extends all A2A SDK error classes (e.g., TaskNotFoundError, TaskNotCancelableError) by adding statusCode and headers properties and updating their constructors to accept and assign these optional HTTP details.
• test/client/transports/rest_transport.spec.ts
  • Adds new test cases to verify that statusCode is correctly set for TaskNotFoundError (404), TaskNotCancelableError (409), PushNotificationNotSupportedError (400), UnsupportedOperationError (405), ContentTypeNotSupportedError (415), InvalidAgentResponseError (502), and AuthenticatedExtendedCardNotConfiguredError (401).
  • Includes a test to confirm that custom response headers like Retry-After and X-RateLimit-Remaining are correctly captured and available on the error object.

Activity

• The author has added new functionality to expose HTTP status codes and headers on SDK error classes.
• The RestTransport has been updated to correctly populate these new error properties.
• Comprehensive unit tests have been introduced to validate the correct behavior across all affected error types and header scenarios.
• Backward compatibility has been explicitly verified, ensuring no regressions for existing code.
• TypeScript linting has been confirmed to pass without new errors.

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[github-actions]

🧪 Code Coverage

⬇️ Download Full Report

	Main	PR	Delta
src/client/transports/rest_transport.ts	85.8%	87.41%	🟢 +1.61%
src/errors.ts	78.57%	100%	🟢 +21.43%
Total	80.22%	80.68%	🟢 +0.46%

Generated by coverage-comment.yml

[gemini-code-assist]

Code Review

This pull request is a great enhancement, exposing HTTP status codes and headers on SDK errors. This will be very useful for consumers to build more robust error handling, for example for rate limiting. The implementation is solid and comes with a comprehensive set of tests.

I've left a couple of suggestions for improvement:

• In src/client/transports/rest_transport.ts, I've suggested a more concise way to convert response headers to an object using Object.fromEntries.
• Regarding src/errors.ts, while the suggestion to introduce a base error class for better maintainability is excellent, we'll defer this refactoring to a future major release to avoid potential breaking changes to the public SDK error interface, as per repository guidelines. A TODO will be added to track this.

Overall, this is a well-executed feature. Addressing the immediate feedback will further improve the code quality.

[gemini-code-assist]

The logic for converting the Headers object to a plain JavaScript object can be simplified. The Headers object is iterable, so you can use Object.fromEntries() for a more concise implementation.

Suggested change

	const headers: Record<string, string> = {};
	response.headers.forEach((value, key) => {
	headers[key] = value;
	});
	return { statusCode: response.status, headers };
	return {
	statusCode: response.status,
	headers: Object.fromEntries(response.headers),
	};