[iamthehimansh]

Please ensure you have read the contribution guide before creating a pull request.

Link to Issue or Description of Change

1. Link to an existing issue (if applicable):

• No existing issue. I searched open and closed issues and PRs for a2a-sdk 1.3 and _httpx_client. fix(a2a): resolve a remote agent's card and client once across invocations #7672 touches _remote_a2a_agent.py but not rebind_client_factory_httpx.

2. Or, if no issue exists, describe the change:

Problem:
With a2a-sdk 1.3.0 (released 2026-10-27, allowed by a2a-sdk>=0.3.4,<2), a RemoteA2aAgent built with a caller-supplied a2a_client_factory sends its requests without the A2A-Version header.

_compat.rebind_client_factory_httpx copies the caller's factory onto ADK's own httpx.AsyncClient. It stamped A2A-Version only inside if hasattr(new_factory, "_httpx_client"). In 1.3.0, ClientFactory.__init__ no longer creates or stores self._httpx_client. It stamps the header only on config.httpx_client (here None) and resolves a client per transport in the new _resolve_http_client(). So the attribute check is now always false, and the rebound client never gets the header.

The same thing shows as a failing unit test on main with 1.3.0:

FAILED tests/unittests/a2a/agent/test_remote_a2a_agent.py::TestRemoteA2aAgentResolution::test_ensure_resolved_uses_custom_factory
E   AttributeError: 'CustomFactory' object has no attribute '_httpx_client'

Solution:

• rebind_client_factory_httpx: still rebind _httpx_client when the factory has it (a2a-sdk 1.0 to 1.2), but stamp A2A-Version on the rebound client whenever IS_A2A_V1, independent of that attribute. 0.3.x behaviour is unchanged.
• New test test_rebind_client_factory_httpx_sets_version_header_on_new_client covers the header directly.
• test_ensure_resolved_uses_custom_factory read the header through the factory's private _httpx_client, which 1.3.0 removed. It now checks the same header on agent._httpx_client, the client ADK actually sends with. This works on both 1.2.x and 1.3.0.

Testing Plan

Unit Tests:

• I have added or updated unit tests for my change.
• All unit tests pass locally.

All runs on macOS 26 (arm64), Python 3.13.15, pip install -e '.[test]'.

Run	a2a-sdk 1.3.0	a2a-sdk 1.2.3
The 2 tests, fix reverted (tests kept)	2 failed	2 passed
The 2 tests, with fix	2 passed	2 passed
pytest tests/unittests/a2a with fix	963 passed, 57 skipped	963 passed, 57 skipped

pyink --check and isort --check-only (repo config) pass on the 3 changed files.

For reference, the full pytest tests/unittests run on main with a2a-sdk 1.3.0 on macOS had 14 failures: this one, and 13 in tests/unittests/integrations/vmaas/test_agent_engine_environment.py. The 13 are macOS-only and unrelated: that test runs the sandbox's commands in the local bash, and macOS stat/base64 don't accept stat -c / base64 -d <file>.

Manual End-to-End (E2E) Tests:

The header on the client RemoteA2aAgent sends with, after _ensure_resolved(), with a2a-sdk 1.3.0:

before:  no factory: A2A-Version = '1.0'
         a2a_client_factory=ClientFactory(ClientConfig(httpx_client=None)): A2A-Version = None
after:   no factory: A2A-Version = '1.0'
         a2a_client_factory=ClientFactory(ClientConfig(httpx_client=None)): A2A-Version = '1.0'

Checklist

• I have read the CONTRIBUTING.md document.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.
• I have manually tested my changes end-to-end.
• Any dependent changes have been merged and published in downstream modules.

Additional context

AI use: this PR was prepared with an AI assistant. It found the problem by running the unit suite and diffing a2a/client/client_factory.py between a2a-sdk 1.2.3 and 1.3.0, wrote the change and tests, and ran every command shown above on my machine (macOS 26.6.2, arm64). The output above is from those runs.

AI-assisted: yes (Cana)