refactor(ui-tui): clean touched resize and sticky prompt paths

Trim comment noise, remove redundant typing, normalize sticky prompt viewport args to top→bottom order, and reuse one sticky viewport helper instead of duplicating the math.

ui-tui/packages/hermes-ink/src/ink/ink.tsx

@@ -463,11 +463,8 @@ export default class Ink {
       this.resetFramesForAltScreen()
       this.needsEraseBeforePaint = true
 
-      // Post-resize drift healer: 160ms after the last resize, force one full
-      // reconcile so Yoga/React catch up to the final viewport and any stale
-      // terminal cells from host-side reflow get repainted away. Ink upstream
-      // and ConPTY/xterm reports point to this as a general resize/reflow
-      // desync class, not an xterm.js-only quirk.
+      // One last repaint after the resize burst settles closes any host-side
+      // reflow drift the normal diff path can't see.
       this.resizeSettleTimer = setTimeout(() => {
         this.resizeSettleTimer = null
 

ui-tui/src/__tests__/viewport.test.ts

@@ -13,7 +13,7 @@ describe('stickyPromptFromViewport', () => {
 
     const offsets = [0, 2, 10, 12, 20]
 
-    expect(stickyPromptFromViewport(messages, offsets, 16, 8, false)).toBe('')
+    expect(stickyPromptFromViewport(messages, offsets, 8, 16, false)).toBe('')
   })
 
   it('shows the latest user message above the viewport when no user message is visible', () => {
@@ -26,6 +26,6 @@ describe('stickyPromptFromViewport', () => {
 
     const offsets = [0, 2, 10, 12, 20]
 
-    expect(stickyPromptFromViewport(messages, offsets, 20, 16, false)).toBe('current prompt')
+    expect(stickyPromptFromViewport(messages, offsets, 16, 20, false)).toBe('current prompt')
   })
 })

ui-tui/src/app/useMainApp.ts

@@ -22,7 +22,7 @@ import type { Msg, PanelSection, SlashCatalog } from '../types.js'
 
 import { createGatewayEventHandler } from './createGatewayEventHandler.js'
 import { createSlashHandler } from './createSlashHandler.js'
-import { type AppLayoutProgressProps, type GatewayRpc, type TranscriptRow } from './interfaces.js'
+import { type GatewayRpc, type TranscriptRow } from './interfaces.js'
 import { $overlayState, patchOverlayState } from './overlayStore.js'
 import { turnController } from './turnController.js'
 import { $turnState, patchTurnState } from './turnStore.js'
@@ -672,16 +672,11 @@ export function useMainApp(gw: GatewayClient) {
     return top + vp >= total - 3
   })()
 
-  const liveProgress = useMemo<AppLayoutProgressProps>(
-    () => ({ ...turn, showProgressArea, showStreamingArea: Boolean(turn.streaming) }),
-    [turn, showProgressArea]
-  )
+  const liveProgress = useMemo(() => ({ ...turn, showProgressArea, showStreamingArea: Boolean(turn.streaming) }), [turn, showProgressArea])
 
   const frozenProgressRef = useRef(liveProgress)
 
-  // When the live tail is offscreen, freeze its snapshot so scroll work doesn't
-  // keep rebuilding the streaming/thinking subtree the user can't see. Thaw as
-  // soon as the viewport comes back near the bottom or the turn finishes.
+  // Freeze the offscreen live tail so scroll doesn't rebuild unseen streaming UI.
   if (liveTailVisible || !ui.busy) {
     frozenProgressRef.current = liveProgress
   }

ui-tui/src/components/appChrome.tsx

@@ -249,28 +249,15 @@ export function StickyPromptTracker({ messages, offsets, scrollRef, onChange }:
   useSyncExternalStore(
     useCallback((cb: () => void) => scrollRef.current?.subscribe(cb) ?? (() => {}), [scrollRef]),
     () => {
-      const s = scrollRef.current
-
-      if (!s) {
-        return NaN
-      }
-
-      const top = Math.max(0, s.getScrollTop() + s.getPendingDelta())
-      const vp = Math.max(0, s.getViewportHeight())
-      const total = Math.max(vp, s.getScrollHeight())
-      const atBottom = s.isSticky() || top + vp >= total - 2
+      const { atBottom, top } = getStickyViewport(scrollRef.current)
 
       return atBottom ? -1 - top : top
     },
     () => NaN
   )
 
-  const s = scrollRef.current
-  const top = Math.max(0, (s?.getScrollTop() ?? 0) + (s?.getPendingDelta() ?? 0))
-  const vp = Math.max(0, s?.getViewportHeight() ?? 0)
-  const total = Math.max(vp, s?.getScrollHeight() ?? vp)
-  const atBottom = (s?.isSticky() ?? true) || top + vp >= total - 2
-  const text = stickyPromptFromViewport(messages, offsets, top + vp, top, atBottom)
+  const { atBottom, bottom, top } = getStickyViewport(scrollRef.current)
+  const text = stickyPromptFromViewport(messages, offsets, top, bottom, atBottom)
 
   useEffect(() => onChange(text), [onChange, text])
 
@@ -395,3 +382,15 @@ interface TranscriptScrollbarProps {
   scrollRef: RefObject<ScrollBoxHandle | null>
   t: Theme
 }
+
+function getStickyViewport(s?: ScrollBoxHandle | null) {
+  const top = Math.max(0, (s?.getScrollTop() ?? 0) + (s?.getPendingDelta() ?? 0))
+  const vp = Math.max(0, s?.getViewportHeight() ?? 0)
+  const total = Math.max(vp, s?.getScrollHeight() ?? vp)
+
+  return {
+    atBottom: (s?.isSticky() ?? true) || top + vp >= total - 2,
+    bottom: top + vp,
+    top
+  }
+}

ui-tui/src/domain/viewport.ts

@@ -18,8 +18,8 @@ const upperBound = (offsets: ArrayLike<number>, target: number) => {
 export const stickyPromptFromViewport = (
   messages: readonly Msg[],
   offsets: ArrayLike<number>,
-  bottom: number,
   top: number,
+  bottom: number,
   sticky: boolean
 ) => {
   if (sticky || !messages.length) {