A "Mark all read" chip appears in the Threads panel header whenever any
thread in the room has unread replies, and sends one threaded receipt per
unread thread (never the root — a root lives in the main timeline and a
receipt there would drag the MAIN read marker backwards, the P6
regression). Honours the private-receipt settings.
Verified: two threads with unread replies → the chip appears, the rows
say "unread" in their labels; after clicking, no unread rows and the chip
is gone.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA
