A step stopped while its calls ran (the user left the page) kept the
provider's whole record of it but answers only for the calls that ran, so
Anthropic and the Responses API refused that thread with HTTP 400 from then
on. Replaying the thread now answers every recorded call that never ran,
which also mends threads already stuck that way.
Claude Sonnet 5.5 at times ends a turn on suggest_follow_ups alone, without
writing its answer, and the turn failed as empty_answer. That step now goes
back to the model whole, its follow-ups answered that the user saw nothing
yet, and their chips come under the answer it then writes. The prompts no
longer say the call goes alone in its step.
Maurice
073db83421