The A2A proxy can return three error shapes:
{"error": "plain string"}
{"error": {"message": "...", "code": ...}}
{"error": {"message": {"nested": "object"}}} ← value at .message is a string
builtin_tools/a2a_tools.py:72 called data["error"].get("message")
without guarding against error being a string, which raised:
AttributeError: 'str' object has no attribute 'get'
This broke every delegation attempt through the legacy a2a_tools path
(the LangChain-wrapped version used by adapter templates). The
SSOT parser a2a_response.py already handled string errors; the
legacy inline sniffer in a2a_tools.py did not.
Fix: branch on isinstance(err, dict/str/other) before calling .get().
Also update both publish-workflow files to remove the dead
`staging` branch trigger — trunk-based migration (PR #109,
2026-05-08) removed the staging branch.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
