Thread images opened the room media lightbox, which looks the event up in
the room's detached media timeline. Thread replies never reach that
timeline, so a thread image always showed "1 / 1" with no prev/next, after
paging the room's media up to six times. The thread panel now builds the
viewer's items from its own root + loaded replies, and "Go to message"
scrolls the thread panel instead of the room.
The viewer gains a "Copy image" button: fetches the displayed media (blob
URL for E2EE, authenticated URL otherwise), re-encodes to PNG when needed,
and writes it via ClipboardItem with a promise so Safari keeps the click's
user activation. Hidden where ClipboardItem is missing. No "open in new
tab": an E2EE blob URL is revoked when the viewer closes and authenticated
media 401s in a bare tab.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA
