fix(desktop): composer wraps long text & expands at the real wrap point

Long unbroken input ran off horizontally and the stacked layout flipped
on a char-count guess (too early). Add wrap rules to the contentEditable
and drive expansion off the editor's actual rendered height via the
resize observer, so it stacks exactly when the text wraps to a 2nd line.

apps/desktop/src/app/chat/composer/index.tsx

@@ -73,6 +73,11 @@ import { VoiceActivity, VoicePlaybackActivity } from './voice-activity'
 
 const COMPOSER_STACK_BREAKPOINT_PX = 320
 
+// A single editor line is ~28px (--composer-input-min-height 1.625rem + 0.5rem
+// vertical padding). Anything taller means the text wrapped to a second line,
+// which is when the composer should expand to the stacked layout.
+const COMPOSER_SINGLE_LINE_MAX_PX = 36
+
 const COMPOSER_FADE_BACKGROUND =
   'linear-gradient(to bottom, transparent, color-mix(in srgb, var(--dt-background) 10%, transparent))'
 
@@ -256,14 +261,13 @@ export function ChatBar({
     }
   }, [urlOpen])
 
-  // Track expansion via cheap heuristics (newline or length threshold) instead
-  // of reading editor.scrollHeight on every keystroke. scrollHeight forces a
-  // synchronous layout flush — measured at 2.27 layouts per character typed
-  // (see scripts/leak-typing.mjs). With ~30 chars before a typical wrap on
-  // composer-default-width, this heuristic flips at roughly the right time
-  // and the user only notices if they type far past the wrap boundary
-  // without a newline; in that case the ResizeObserver below catches it via
-  // a height delta and we still expand.
+  // Expansion (input on its own full-width row, controls below) is driven by
+  // the editor's *actual* rendered height via the ResizeObserver in
+  // syncComposerMetrics — it only fires when the text genuinely wraps to a
+  // second line, so the layout flips exactly at the wrap point rather than at
+  // a guessed character count. We only handle the two cases the observer
+  // can't: an explicit newline (expand before layout settles) and an emptied
+  // draft (collapse back). We never read scrollHeight per keystroke.
   useEffect(() => {
     if (!draft) {
       setExpanded(false)
@@ -275,7 +279,7 @@ export function ChatBar({
       return
     }
 
-    if (draft.includes('\n') || draft.length > 60) {
+    if (draft.includes('\n')) {
       setExpanded(true)
     }
   }, [draft, expanded])
@@ -311,6 +315,18 @@ export function ChatBar({
       }
     }
 
+    // Expand once the input has actually wrapped past a single line. The
+    // observer only fires on real size changes, so this reads scrollHeight at
+    // most once per wrap (not per keystroke). One line ≈ 28px (1.625rem
+    // min-height + padding); a second line clears ~36px. We only ever expand
+    // here — collapse is handled by the emptied-draft effect to avoid
+    // oscillating across the wrap boundary as the input switches widths.
+    const editor = editorRef.current
+
+    if (editor && editor.scrollHeight > COMPOSER_SINGLE_LINE_MAX_PX) {
+      setExpanded(true)
+    }
+
     if (height > 0) {
       const bucket = Math.round(height / 8) * 8
 
@@ -330,7 +346,7 @@ export function ChatBar({
     }
   }, [])
 
-  useResizeObserver(syncComposerMetrics, composerRef, composerSurfaceRef)
+  useResizeObserver(syncComposerMetrics, composerRef, composerSurfaceRef, editorRef)
 
   useEffect(() => {
     return () => {
@@ -1109,7 +1125,7 @@ export function ChatBar({
         autoCapitalize="off"
         autoCorrect="off"
         className={cn(
-          'min-h-(--composer-input-min-height) max-h-(--composer-input-max-height) overflow-y-auto bg-transparent pb-1 pr-1 pt-1 leading-normal text-foreground outline-none disabled:cursor-not-allowed',
+          'min-h-(--composer-input-min-height) max-h-(--composer-input-max-height) overflow-y-auto whitespace-pre-wrap break-words [overflow-wrap:anywhere] bg-transparent pb-1 pr-1 pt-1 leading-normal text-foreground outline-none disabled:cursor-not-allowed',
           'empty:before:content-[attr(data-placeholder)] empty:before:text-muted-foreground/60',
           '**:data-ref-text:cursor-default',
           stacked && 'pl-3',