Switch the real 'Run agent' step to --format json (replacing the two
TEMP/DEBUG schema-discovery commits da6f0d5/d0ddb06), capture the raw
event stream, and reconstruct the plain-text reply from the assistant
'text' parts so the existing Publish logic is unchanged.
Add a 'Build activity log' step that filters the event stream to
tool_use (with truncated title/input) and text (reasoning) events.
The Publish step posts that trail as a separate collapsible comment on
the PR thread (dev agents only — comment-only roles do no tool calls).
This is additive to the existing summary/PR-description comment.
Reasoning reuse on a follow-up run is free: the existing 'fetch full
issue thread' step already re-feeds all prior comments (including this
new log comment) into the next run's prompt, so the agent sees what it
did last time.
