[Bug]: REST client raises AttributeError when an HTTP error body is not a google.rpc.Status

Finding: In a2a-python, per an external report on main at commit dac7d9d, RestTransport raises a bare AttributeError ("'str' object has no attribute 'get'") instead of an A2A client error when a REST call fails with an HTTP error whose JSON body is not a google.rpc.Status object (https://github.com/a2aproject/a2a-python/issues/1299). The report was created and updated on 2026-10-02, and the issue is now CLOSED. Reported conditions: the reporter says this typically happens when a proxy or gateway answers instead of the agent, for example an OAuth layer returning 401 with {"error": "invalid_token"}, or a load balancer returning 502 with a JSON string (issue #1299). The reporter's table lists 401, 404, 502, 500 and 503 responses with string, list, plain-string or null bodies, all raising AttributeError. Expected behavior per the reporter is HTTP-status-based fallback: MethodNotFoundError for 404 and A2AClientError otherwise. The reporter says well-formed google.rpc.Status bodies still map correctly, for example TASK_NOT_FOUND to TaskNotFoundError, and that streaming calls and the v0.3 compat REST transport fail similarly (issue #1299). Reporter's hypothesized cause (not maintainer-confirmed): _parse_rest_error in src/a2a/client/transports/rest.py assumes payload['error'] is an object and calls .get on it, while _handle_http_error only catches JSONDecodeError/ValueError, so the status fallback never runs (issue #1299). A short reproduction using httpx.MockTransport and RestTransport.get_task is in the issue body; it was not run by triage or KFA. Status: the reporter said a small fix with regression tests was ready and a PR would be opened, but no PR, commit or released version is linked in the supplied material. The issue is closed, but closure alone does not establish that a fix merged or shipped. Fix status is therefore UNKNOWN, and no workaround was offered. Limitation: this is a single external report. It is not reproduced by KFA, and comment coverage is partial. Affected released versions are unknown. Anyone hitting this should check the repository for a linked fix before relying on the behavior.