fix(mobile): draw a whole character in an avatar fallback

[Chessing234]

The mobile half of #5992, which fixed the same bug in desktop's getInitials. No issue filed.

Seven avatar fallbacks took their letter with label[0] or label.substring(0, 1). Both return a single UTF-16 code unit, so a display name starting with an emoji or a CJK Extension B character — ordinary in Chinese and Japanese given names — produced half a surrogate pair, and the avatar drew �:

• UserProfile.initial (the profile model every surface reads)
• invite and channel-management labels
• the members sheet
• both pulse note surfaces
• people results in search

Reading grapheme clusters also keeps a base letter together with its combining marks, so a Devanagari or Burmese name keeps its vowel sign instead of showing a bare consonant.

This follows the codebase's own practice rather than introducing anything. characters is already a direct dependency in pubspec.yaml, and mobile already reaches for it wherever text has to be treated as text — shared/emoji/emoji_only.dart iterates .characters, and the message preview in features/channels/message_actions.dart truncates by .characters rather than by index. The avatar fallbacks were the ones that hadn't caught up.

The pubkey-derived fallbacks (forum_post_card.dart, forum_thread_page.dart, user_profile_sheet.dart) are deliberately untouched: hex is ASCII, and taking one code unit of it was never wrong.

Verification note (corrected). An earlier version of this description said there was no Flutter or Dart SDK on this machine. That was wrong — the repo pins both through hermit (./bin/dart, ./bin/flutter), which I had been using all along for ./bin/cargo without noticing. I am running the mobile checks and will post the results in the thread.

Note: I'm an outside contributor, so the workflow runs here sit at action_required until a maintainer approves them; only the DCO check reports on its own.

[themiguelamador]

The shared avatarInitial helper is correct and its focused test passes, but the same bug remains in two avatar fallbacks:

• mobile/lib/features/channels/compose_bar/suggestions.dart still uses name[0].toUpperCase(). This still renders half a surrogate pair for astral names and can throw when a candidate label is empty.
• mobile/lib/features/channels/channels_page/community.dart still uses trimmedName.substring(0, 1).toUpperCase(), so community names beginning with an astral character still render U+FFFD.

Please route both through avatarInitial (adding the imports to the parent part libraries). Minor documentation correction: “every emoji” is outside the BMP is too broad; “most emoji” is accurate.

I applied and verified this exact patch locally: the focused Flutter test passes, flutter analyze reports no issues, and the mobile pre-commit gate passes. I attempted to push the signed-off fix directly because maintainer_can_modify is true, but GitHub returned 403 for my account.

[Chessing234]

both confirmed and fixed in c46fb059.

• compose_bar/suggestions.dart:50 — name[0].toUpperCase(), now avatarInitial(name). you're right that it also throws outright on an empty label rather than just rendering badly; avatarInitial returns ?, which is what the surrounding code already wanted.
• channels_page/community.dart:493 — trimmedName.substring(0, 1), now avatarInitial(trimmedName ?? ''), keeping the existing null/empty → ? behaviour.

both are part of libraries as you said, so the imports went on compose_bar.dart and channels_page.dart rather than the part files.

grep -rn "name\[0\]\|substring(0, 1)" mobile/lib is now clean apart from the helper's own doc comment. the pubkey-derived fallbacks in forum_post_card.dart, forum_thread_page.dart, user_profile_sheet.dart, small_avatar.dart, inbox_row.dart and reaction_row.dart are deliberately untouched — hex is ascii, so one code unit was never wrong there. say the word if you'd rather they were uniform anyway.

wording: fixed — "most emoji" in the doc.

i deleted my earlier comment on this pr because it was wrong on a point of fact. it said there was no flutter or dart sdk on this machine and that i therefore couldn't verify mobile changes. that isn't true — the repo pins both through hermit (./bin/dart, ./bin/flutter), which i'd been using all along for ./bin/cargo without noticing. i'm bootstrapping it now and will post flutter analyze and flutter test results for this branch rather than leaving it on your verification.

[themiguelamador]

Re-reviewed current head c46fb059a. This update resolves every prior finding: the compose mention and community avatar fallbacks now use avatarInitial, the imports are correctly placed in their parent libraries, and the Unicode documentation is accurate.

Verified with flutter analyze, Dart formatting, and the affected helper, compose-bar, and channels-page test files (129/129 passed). No remaining findings.

[Chessing234]

verification for this branch, now that i have the toolchain i wrongly said i didn't:

• dart format --output=none --set-exit-if-changed . — clean
• flutter analyze — no issues found
• flutter test — 1,422 passed

so your local run and mine agree. nothing further needed from you on this one.