[v0ropaev]

Description

The v0.3 REST client in the compat package did not recognize the error bodies that this SDK's own v0.3 REST routes send. CompatRestTransport._handle_http_error only mapped a body shaped like {"type": "TaskNotFoundError", "message": ...}. The v0.3 routes mounted by create_rest_routes(..., enable_v0_3_compat=True) go through the same rest_error_handler as v1.0 and return a google.rpc.Status with an ErrorInfo reason, for example

404 {"error":{"code":404,"status":"NOT_FOUND","message":"Task not found","details":[{"@type":"type.googleapis.com/google.rpc.ErrorInfo","reason":"TASK_NOT_FOUND","domain":"a2a-protocol.org","metadata":{}}]}}

So against one server with both v0.3 bindings enabled, the two clients disagreed.

CompatJsonRpcTransport   get_task(missing)        -> TaskNotFoundError: Task not found
CompatJsonRpcTransport   cancel_task(missing)     -> TaskNotFoundError: Task not found
CompatJsonRpcTransport   cancel_task(completed)   -> TaskNotCancelableError: Task cannot be canceled
CompatRestTransport      get_task(missing)        -> MethodNotFoundError: Resource not found: http://testserver/v1/tasks/nope
CompatRestTransport      cancel_task(missing)     -> MethodNotFoundError: Resource not found: http://testserver/v1/tasks/nope:cancel
CompatRestTransport      cancel_task(completed)   -> A2AClientError: HTTP Error 400: Client error '400 Bad Request' ...

After the change all three REST rows raise TaskNotFoundError, TaskNotFoundError and TaskNotCancelableError, matching JSON-RPC.

The fix passes the parsed body to _parse_rest_error from a2a.client.transports.rest, which is what the v1.0 RestTransport already uses, and raises the mapped error when there is one. That covers every reason in A2A_REASON_TO_ERROR, not only the two task errors above. Against the same app, send_message with an unsupported content type now raises ContentTypeNotSupportedError and create_task_push_notification_config raises PushNotificationNotSupportedError when push is not supported, where both used to be a bare A2AClientError: HTTP Error 400.

The existing type lookup and the 404 and generic status fallback stay in place after it. I could not find any server in this repo or in a2a-sdk 0.3.26 that sends the type shape, but it is cheap to keep and an existing test covers it. A real 0.3.x Python server answers with {"message": ...} and no reason, so against that server a missing task still comes back as MethodNotFoundError. That is unchanged here and would need its own fix.

Tests added in tests/compat/v0_3/test_rest_transport.py. One is a parametrized unit test with the exact bodies the server produces for TASK_NOT_FOUND (404) and TASK_NOT_CANCELABLE (400). The other runs CompatRestTransport against a Starlette app built with create_rest_routes(enable_v0_3_compat=True) over httpx.ASGITransport, parametrized over get on a missing task, cancel on a missing task and cancel on a completed one.

With the source change reverted, uv run pytest tests/compat/v0_3/test_rest_transport.py gives 5 failed, 32 passed (the new cases get MethodNotFoundError and A2AClientError: HTTP Error 400). With it, 37 passed. Full uv run pytest is 2496 passed, 203 skipped, 4 xfailed, 1 xpassed. ./scripts/lint.sh passes, and --cov=src puts compat/v0_3/rest_transport.py at 96% with the new lines covered.

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[github-actions]

🧪 Code Coverage (vs main)

⬇️ Download Full Report

	Base	PR	Delta
src/a2a/compat/v0_3/rest_transport.py	95.63%	95.76%	🟢 +0.13%
Total	93.40%	93.40%	⚪️ 0.00%

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