T23a: AI chat, messages

- messages: yours in a quiet bubble, the assistant's as prose beside its mark,
  system notes, errors; avatars, headers with model and time, footers
- MessageList over gpui's bottom-aligned list: drawn near the view, held at the
  newest, counting arrivals while away; a way back down; day separators
- streaming text and markdown reveal toward the text as it grows, with a caret;
  a blinking cursor before the first words
- CodeBlock with language, copy, run, apply, download and folding;
  MarkdownRenderer::code lets messages draw fences with it
- pictures, grids, files, voice notes, video over host frames, link previews
- quotes, actions, an editor that takes focus, versions, regenerate, stop and
  continue
- errors with retry, a rate limit counting down, feedback, thinking blocks
- gallery: the AI Chat page with scripted states

tasks/ch21-30.md

@@ -76,39 +76,39 @@
 
 ## T23a AI Chat · Messages — `src/chat`
 
-- [ ] ChatContainer
-- [ ] MessageList — virtualized, stick to bottom, new-message hint
-- [ ] MessageBubble — user, assistant, system, error
-- [ ] MessageAvatar
-- [ ] MessageHeader
-- [ ] MessageFooter
-- [ ] StreamingText
-- [ ] StreamingMarkdown
-- [ ] StreamingCursor
-- [ ] CodeBlock — language, copy, download, run, fold, apply
-- [ ] MathBlock → `typography::Latex`
-- [ ] TableBlock → `documents::MarkdownRenderer`
-- [ ] MermaidRenderer → `documents::MermaidBlock`
-- [ ] ImageMessage / ImageGrid
-- [ ] FileMessage
-- [ ] AudioMessage
-- [ ] VideoMessage — host frames
-- [ ] LinkPreviewCard
-- [ ] QuoteReply
-- [ ] MessageActions
-- [ ] MessageEditor
-- [ ] BranchNavigator
-- [ ] RegenerateButton
-- [ ] StopGeneratingButton
-- [ ] ContinueButton
-- [ ] ErrorMessage / RetryMessage
-- [ ] RateLimitNotice
-- [ ] FeedbackForm
-- [ ] ScrollToBottomButton
-- [ ] DateSeparator
-- [ ] ThinkingBlock / ReasoningPanel
-- [ ] ThinkingIndicator
-- [ ] ThinkingDuration
+- [x] ChatContainer
+- [x] MessageList — virtualized, stick to bottom, new-message hint
+- [x] MessageBubble — user, assistant, system, error
+- [x] MessageAvatar
+- [x] MessageHeader
+- [x] MessageFooter
+- [x] StreamingText
+- [x] StreamingMarkdown
+- [x] StreamingCursor
+- [x] CodeBlock — language, copy, download, run, fold, apply
+- [x] MathBlock → `typography::Latex`
+- [x] TableBlock → `documents::MarkdownRenderer`
+- [x] MermaidRenderer → the host draws the SVG; `chat::ImageMessage` shows it
+- [x] ImageMessage / ImageGrid
+- [x] FileMessage
+- [x] AudioMessage
+- [x] VideoMessage — host frames
+- [x] LinkPreviewCard
+- [x] QuoteReply
+- [x] MessageActions
+- [x] MessageEditor
+- [x] BranchNavigator
+- [x] RegenerateButton → `chat::regenerate_button`
+- [x] StopGeneratingButton → `chat::stop_button`
+- [x] ContinueButton → `chat::continue_button`
+- [x] ErrorMessage / RetryMessage → `chat::ErrorMessage`, over `feedback::Alert`
+- [x] RateLimitNotice
+- [x] FeedbackForm
+- [x] ScrollToBottomButton
+- [x] DateSeparator
+- [x] ThinkingBlock / ReasoningPanel → `chat::ThinkingBlock`
+- [x] ThinkingIndicator
+- [x] ThinkingDuration
 
 ## T23b AI Chat · Citations