The new-message picker laid out every recipient inside an outer scroll
view. Searching or changing selection could therefore mount the whole
directory in one frame. Use a bounded sliver viewport so offscreen
recipients stay lazy while the search field and selection chips still
scroll above the keyboard.
### Validation
- Current-head CI passed, including all Flutter test shards, Android,
and native/release Swift jobs. Code and security reviews found no
issues. After merging main and retaining both test imports, all 81
channel-page tests and the full mobile check/test suite passed.
- Added a 200-person widget regression: the original mounts all 200
rows; the fix keeps fewer than 30 mounted through open, search,
selection and removal, and can scroll to the final recipient. Covers
no-match and closing too.
- Strengthened the keyboard/chip test to verify the eight-recipient
limit and that removing a chip makes the ninth recipient reachable.
- All 79 channel-page tests passed; the strengthened limit test and
Flutter analysis passed.
- Native iOS simulator build passed. On a separately cloned paired
simulator, verified populated directory/search, eight selected
recipients, limit message, removal, no-match, scrolling to the final
recipient and close without creating a conversation. Debug/AX
instrumentation and a newer Flutter baseline make this functional
validation, not a controlled release-speed benchmark.
- Normal pre-push mobile checks passed, including formatting, analysis
and the full Flutter test suite. Required CI exposed existing formatting
in `message_carousel_preview_cases.dart`; a separate formatter-only
commit corrects it.
- The full local repository gate hit an unrelated Rust failure in
`buzz-acp::signals_cancel_startup_turn_and_pending_stdin_without_hanging`
(exit status `None` rather than `Some(143)`). No Rust code changed. The
gate stopped at unit tests, so later build stages did not run.
### Related issue
No duplicate recipient-layout fix found in the existing issue/PR search.
### Before and after
The synthetic 200-person picker renders identically before and after
(with a reserved keyboard inset). One image represents both; mounted-row
assertions establish the performance mechanism separately.
---------
Signed-off-by: Tom Brow <tomb@block.xyz>
93114b4279
