fix(a2a-server): mount express.json before a2a sdk routes

[Anurag-M1]

Fixes #29073

Description

In packages/a2a-server/src/http/app.ts, express.json() was mounted after appBuilder.setupRoutes(expressApp, ''). As a result, A2A SDK routes (such as POST /) received req.body as undefined, breaking JSON-RPC parsing.

Changes

• Mounted expressApp.use(express.json()) prior to appBuilder.setupRoutes in createApp().
• Added unit test in packages/a2a-server/src/http/app.test.ts to verify JSON-RPC body parsing on SDK routes.

[gemini-code-assist]

Summary of Changes

Hello, 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 resolves an issue where A2A SDK routes were receiving undefined request bodies due to incorrect middleware registration order. By moving the JSON parsing middleware before the route initialization, the application now correctly processes incoming JSON-RPC requests.

Highlights

• Middleware Ordering: Reordered the express.json() middleware to execute before the A2A SDK route setup, ensuring that request bodies are correctly parsed for JSON-RPC operations.
• Regression Testing: Added a new unit test to verify that A2A SDK routes successfully handle and parse JSON payloads, preventing future regressions.

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[github-actions]

📊 PR Size: size/S

• Lines changed: 16
• Additions: +15
• Deletions: -1
• Files changed: 2

[gemini-code-assist]

Code Review

This pull request moves the registration of the JSON body parser middleware before setting up the A2A SDK routes to ensure proper request parsing, and adds a corresponding E2E test. The reviewer suggests optimizing the new test by reusing the existing shared application instance instead of re-initializing it with createApp(), which is redundant and inefficient.

[gemini-code-assist]

Re-initializing the application by calling createApp() inside an individual test case is redundant and inefficient. The test suite already sets up a shared app instance in the beforeAll hook (line 115). Re-running createApp() performs expensive operations like loading settings, config, and changing the working directory (process.chdir), which can lead to test flakiness and slow down the test suite. You should reuse the existing app instance instead.

Suggested change

	const app = await createApp();
	const res = await request(app)
	const res = await request(app)