Parallel root-cause analysis: during body.chat-opening the pane is momentarily ~0 width; word-break:
break-word / overflow-wrap:anywhere let bubbles collapse to 1-GLYPH min-content, so pre-wrap text wraps
into hundreds of lines (5684px 'balloon'); same inflates the empty/draft textarea (autoGrow->140=4 lines);
and translateX(100%) of a ~0-width pane = no travel = the 'jump'. The tall box hid in anonymous line
boxes (renderMsgBody emits bare text nodes), which is why the probe only saw the 84px timestamp span.
Fixes (all @media max-width:760px / chat-opening scoped, desktop untouched):
1. .bubble: word-break:normal + overflow-wrap:break-word (min-content = longest word, never collapses)
2. mobile bubble group: overflow-wrap:anywhere -> break-word
3. .msg-link: word-break:break-word -> overflow-wrap:break-word (URL-only msgs can't reopen the hole)
4. body.chat-opening .content: width:100vw -> definite width, no collapse frame, real slide travel
Build marker -> 2026-07-18-batch117.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Sravan
1f5b4bd42c