refactor: define and export helper API for Extensions

[ishymko]

Description

Define types and utility functions for extensions to export for external usage and share between client and server.

Re #218 #219

[gemini-code-assist]

Summary of Changes

Hello @ishymko, 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 refactors the management of A2A protocol extensions by introducing explicit ExtensionId and ExtensionIds types, along with a set of utility functions. This change aims to provide a more robust and consistent way to handle extension identifiers across both client and server components, improving type safety and simplifying the logic for processing extension-related service parameters.

Highlights

• New Extension Types: Introduced ExtensionId (a string alias) and ExtensionIds (an array of ExtensionId) to standardize how A2A protocol extensions are represented.
• Extension Utility Functions: Added a new ExtensionIds object with static methods for creating, parsing from service parameters, and converting ExtensionIds to service parameter strings.
• Refactored Extension Handling: Updated client-side withA2AExtensions and server-side ServerCallContext to leverage the new ExtensionIds types and utility functions, replacing previous Set<string> usage.
• Improved Service Parameter Parsing: The server-side handlers (JSON-RPC and REST) now use ExtensionIds.parseServiceParameter to correctly interpret the HTTP_EXTENSION_HEADER.
• Dedicated Test Coverage: A new test file test/extensions.spec.ts has been added to ensure the correctness of the new ExtensionIds utility functions.

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[gemini-code-assist]

Code Review

This pull request refactors the handling of A2A protocol extension identifiers by introducing dedicated types (ExtensionId, ExtensionIds) and a set of utility functions. This improves type safety and centralizes the logic for parsing and formatting extension headers. The changes are applied consistently across client and server-side code, including service parameter creation, context management, and request handlers. The tests are also updated and expanded to cover the new utilities.

My review focuses on a couple of critical runtime errors due to unhandled undefined values from request headers, and some suggestions to improve code clarity and maintainability.

[ishymko]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces a dedicated ExtensionId type and an ExtensionIds utility object to manage A2A protocol extensions. This refactoring centralizes the logic for parsing, serializing, and managing extension identifiers, improving type safety and code organization. The changes are consistently applied across the client and server components, and new unit tests have been added to ensure the correctness of the ExtensionIds utility. The removal of the getRequestedExtensions utility from src/server/utils.ts and its replacement with the new ExtensionIds.parseServiceParameter is a good cleanup.