An OSC longer than the 8 KiB carry buffer (OSC 52 clipboard writes,
inline images) was dropped mid-sequence, so its BEL terminator was then
scanned as a bare bell and marked the pane Unread. Skip the rest of a
dropped OSC through its terminator instead.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>