When streaming already delivered the final reply, gateway/run_turn.py's
_hmwa_deliver_turn_response suppresses the normal adapter.send() and returns
None, so A2AAdapter.send() — the only path that ever carries reply text —
never runs. on_processing_complete() then resolves the pending A2A task
future through its SUCCESS default, which was hardcoded to "", so every
streamed A2A reply lands as TASK_STATE_COMPLETED with no status.message and
no artifacts (#116944).
_hmwa_deliver_turn_response already stashes the true final text on
event._streamed_final_response for exactly this situation (the same stash
_final_text_for_post_turn_hooks reads for /goal and /loop). Read it as the
SUCCESS-path fallback text instead of "".
(cherry picked from commit 638041af046ab149a356a7e5107d52c2e6a3c9a8)
7efacc8f62