Get the status of an on-demand refresh

Poll the status of an on-demand refresh started by POST /documents/:uuid/refresh. Pass the thread_uuid returned by that call. Returns a coarse state (running | completed | completed_unknown_outcome | failed), the skill-level skill_status when parseable (completed | completed_no_changes | completed_locked | failed), a one-line summary, and completed_at when the run terminates.

completed_unknown_outcome means the agent finished talking but no recognized terminal status code was present in its reply — callers should surface summary to the user verbatim rather than assume the refresh succeeded.

Possession of the unguessable thread_uuid is the access proof — within a tenant, any caller with the handle can poll its status. Callers should poll until state != "running" — refreshes typically complete within 10-60 seconds.