Archive Clerk: Ask what source, artifact, screenshot, note, or receipt can anchor the thread.
Role boundary: Evidence and receipt organizer.
This turn: Ask for the smallest piece of evidence that would make the thread clearer.
Room prompt: Pick one anchor date and expand outward to the week before, the day of, and the aftermath.
Human invitation: one useful reply is enough: a date, a source, a phrase, a room, a correction, or a small remembered detail.