[Bug]: grpc_handler maps 3 A2A errors to FAILED_PRECONDITION instead of UNIMPLEMENTED, and doesn't validate A2A-Version at all

[avilleroy51]

What happened?

grpc_handler.py's _ERROR_CODE_MAP (src/a2a/server/request_handlers/grpc_handler.py:84-98) maps 3 of the 9 A2A error types to the wrong gRPC status code, diverging from the canonical binding table in the spec (specification.md "Custom Binding Requirements" / error-code-mappings section):

A2A Error Type	Spec gRPC Status	SDK gRPC Status
PushNotificationNotSupportedError	UNIMPLEMENTED	FAILED_PRECONDITION ❌
UnsupportedOperationError	UNIMPLEMENTED	FAILED_PRECONDITION ❌
VersionNotSupportedError	UNIMPLEMENTED	FAILED_PRECONDITION ❌

_ERROR_CODE_MAP: dict[type[A2AError], grpc.StatusCode] = {
    ...
    types.PushNotificationNotSupportedError: grpc.StatusCode.FAILED_PRECONDITION,
    types.UnsupportedOperationError: grpc.StatusCode.FAILED_PRECONDITION,
    ...
    types.VersionNotSupportedError: grpc.StatusCode.FAILED_PRECONDITION,
}

The other 6 mappings (TaskNotFoundError, TaskNotCancelableError, ContentTypeNotSupportedError, InvalidAgentResponseError, ExtendedAgentCardNotConfiguredError, ExtensionSupportRequiredError) are all correct against the same table.

Second, related bug: gRPC transport doesn't validate A2A-Version at all

jsonrpc_dispatcher.py and rest_dispatcher.py both guard their handlers with @validate_version(constants.PROTOCOL_VERSION_1_0), which raises VersionNotSupportedError for an unsupported A2A-Version. grpc_handler.py has no equivalent — a SendMessage gRPC call with metadata a2a-version: 99.0 is processed normally instead of being rejected. Per spec (specification.md:739): "Agents MUST process requests using the semantics of the requested A2A-Version... If the version is not supported by the interface, agents MUST return a VersionNotSupportedError."

Reproduction

Against a standard DefaultRequestHandlerV2-backed gRPC server:

import grpc
metadata = [("a2a-version", "99.0")]
client.stub.SendMessage(proto_request, metadata=metadata)
# succeeds — no VersionNotSupportedError, no version check at all

For the status-code mismatch, trigger any PushNotificationNotSupportedError (e.g. call CreatePushNotificationConfig when capabilities.push_notifications is false) over gRPC and inspect e.code() — it's FAILED_PRECONDITION, not UNIMPLEMENTED.

We hit both while running the official a2a-tck MUST-level gRPC suite against a reference SUT built on this SDK — GRPC-ERR-002 fails on test_push_not_supported_returns_unimplemented and test_version_not_supported_returns_unimplemented for exactly these reasons.

Expected

• Fix the 3 entries in _ERROR_CODE_MAP to UNIMPLEMENTED, matching the other 6 and the spec table.
• Apply the same version-validation the HTTP dispatchers already do to the gRPC transport (a @validate_version-equivalent, or an explicit check in GrpcHandler reading the a2a-version metadata key).

Happy to send a PR for both if useful.

[avilleroy51]

Fixed in #1167.

[rohityan]

Hi @avilleroy51 , Thank you for reporting this and contributing in #1167 to fix this. Your diagnosis of the issue is accurate.
In your fix within _validate_a2a_version(), if a user supplies a custom GrpcServerCallContextBuilder that does not populate state['headers'], it currently defaults to '0.3' and would reject valid 1.0 requests. Consider adding a fallback to read invocation_metadata() directly from server_context.state.get('grpc_context') if headers is missing.
Also could you add unit tests in test_grpc_handler.py explicitly asserting that an incompatible version (e.g. a2a-version: 99.0) or an absent version metadata properly triggers VersionNotSupportedError / StatusCode.UNIMPLEMENTED.
Assigning this issue to you till the PR gets reviewed.