chore(tui): /clean recent perf work — KISS/DRY pass

24 files, -319 LoC. Behaviour preserved, 369/369 tests green.

- hermes-ink caches: shared lruEvict helper for the four parallel LRU
  caches (stringWidth, wrapText, sliceAnsi, lineWidth); touch-on-read
  stays inlined per cache; tightened output.ts skip-slice fast path.
- wheelAccel: trimmed provenance header, collapsed env parsing, ternary
  dispatch in computeWheelStep.
- perfPane: folded ensureLogDir into once-flag, spread-with-overrides
  for fastPath/phases instead of full rebuilds.
- env: extracted truthy() (used 4×).
- virtualHeights: collapsed user/diff/slash height bumps; trail+todos
  estimate.
- useInputHandlers: scrollIdleTimer cleanup on unmount, ?? undefined
  shorthand.
- useMainApp: dropped dead liveTailVisible IIFE and liveProgress
  indirection.
- appLayout, markdown, messageLine, entry: vertical rhythm, dropped
  narration comments, inlined one-shot vars.
- fix: empty catch blocks → /* best-effort */ for no-empty lint.

ui-tui/src/components/appLayout.tsx

@@ -30,14 +30,18 @@ const TranscriptPane = memo(function TranscriptPane({
 }: Pick<AppLayoutProps, 'actions' | 'composer' | 'progress' | 'transcript'>) {
   const ui = useStore($uiState)
 
-  // Index of the latest user message — LiveTodoPanel is rendered as a child
-  // of that row so it visually belongs to the user's prompt and follows it
-  // during scroll. Falls back to -1 when no user message exists yet (empty
-  // session); LiveTodoPanel then doesn't render at all.
+  // LiveTodoPanel rides as a child of the latest user-message row so it
+  // visually belongs to the prompt and follows it during scroll. -1 when
+  // empty → row.index === -1 is always false → no render.
   const lastUserIdx = useMemo(() => {
-    for (let i = transcript.historyItems.length - 1; i >= 0; i--) {
-      if (transcript.historyItems[i].role === 'user') return i
+    const items = transcript.historyItems
+
+    for (let i = items.length - 1; i >= 0; i--) {
+      if (items[i].role === 'user') {
+        return i
+      }
     }
+
     return -1
   }, [transcript.historyItems])
 
@@ -259,18 +263,9 @@ export const AppLayout = memo(function AppLayout({
 }: AppLayoutProps) {
   const overlay = useStore($overlayState)
 
-  // Inline mode: skip <AlternateScreen> so the TUI renders into the
-  // primary buffer and the terminal's native scrollback can capture rows
-  // that scroll off the top.  Mouse tracking is still enabled via
-  // AlternateScreen when the wrapper is on; in inline mode we leave it
-  // to the host terminal, which typically does wheel → scrollback.
-  //
-  // `Fragment` (via alias so the JSX stays legible) drops the alt-screen
-  // constraint while keeping the inner layout identical.  Content height
-  // will then follow flex-column growth, which means the ScrollBox below
-  // grows beyond the viewport — the terminal's primary buffer scrolls
-  // old rows off the top into native scrollback.  Composer + progress
-  // stay at the bottom via normal flow (they're the last siblings).
+  // Inline mode skips AlternateScreen so the host terminal's native
+  // scrollback captures rows scrolled off the top; composer + progress
+  // stay anchored via normal flex-column flow.
   const Shell = INLINE_MODE ? Fragment : AlternateScreen
   const shellProps = INLINE_MODE ? {} : { mouseTracking }
 
@@ -305,9 +300,6 @@ export const AppLayout = memo(function AppLayout({
               <ComposerPane actions={actions} composer={composer} status={status} />
             </PerfPane>
 
-            {/* FPS counter overlay: pinned to the bottom row, right
-                aligned, gated on HERMES_TUI_FPS. Returns null + skips
-                this subtree when disabled (zero cost). */}
             {SHOW_FPS && (
               <Box flexShrink={0} justifyContent="flex-end" paddingRight={1}>
                 <FpsOverlay />

ui-tui/src/components/fpsOverlay.tsx

@@ -1,10 +1,4 @@
-// FPS counter overlay — renders in the bottom-right corner when
-// HERMES_TUI_FPS=1.  Zero-cost when disabled (returns null at the
-// top of the component; React skips the whole subtree).
-//
-// Subscribes to $fpsState via nanostores.  The store is only updated
-// when the env flag is on (trackFrame is undefined otherwise), so we
-// also gate the subscription on SHOW_FPS to avoid a useless listener.
+// FPS counter overlay (HERMES_TUI_FPS=1). Zero-cost when disabled.
 
 import { Text } from '@hermes/ink'
 import { useStore } from '@nanostores/react'
@@ -12,17 +6,7 @@ import { useStore } from '@nanostores/react'
 import { SHOW_FPS } from '../config/env.js'
 import { $fpsState } from '../lib/fpsStore.js'
 
-const fpsColor = (fps: number) => {
-  if (fps >= 50) {
-    return 'green'
-  }
-
-  if (fps >= 30) {
-    return 'yellow'
-  }
-
-  return 'red'
-}
+const fpsColor = (fps: number) => (fps >= 50 ? 'green' : fps >= 30 ? 'yellow' : 'red')
 
 export function FpsOverlay() {
   if (!SHOW_FPS) {
@@ -35,14 +19,10 @@ export function FpsOverlay() {
 function FpsOverlayInner() {
   const { fps, lastDurationMs, totalFrames } = useStore($fpsState)
 
-  // Zero-pad to stable width so the corner doesn't jitter as digits
-  // come and go.  Format: " 62fps  0.3ms #12345"
-  const fpsStr = fps.toFixed(1).padStart(5)
-  const durStr = lastDurationMs.toFixed(1).padStart(5)
-
+  // Zero-pad widths so digit churn doesn't jitter the corner.
   return (
     <Text color={fpsColor(fps)}>
-      {fpsStr}fps · {durStr}ms · #{totalFrames}
+      {fps.toFixed(1).padStart(5)}fps · {lastDurationMs.toFixed(1).padStart(5)}ms · #{totalFrames}
     </Text>
   )
 }

ui-tui/src/components/markdown.tsx

@@ -1,5 +1,5 @@
 import { Box, Link, Text } from '@hermes/ink'
-import { memo, useMemo, type ReactNode } from 'react'
+import { memo, type ReactNode, useMemo } from 'react'
 
 import { ensureEmojiPresentation } from '../lib/emoji.js'
 import { highlightLine, isHighlightable } from '../lib/syntax.js'
@@ -213,26 +213,23 @@ function MdInline({ t, text }: { t: Theme; text: string }) {
   return <Text>{parts.length ? parts : <Text>{text}</Text>}</Text>
 }
 
-// Cross-instance parsed-children cache. `Md` is mounted fresh whenever a
-// virtualized row enters the mount window — useMemo's per-instance cache
-// doesn't survive remounts, so PageUp into cold/resumed history reparses
-// every row (markdown scan + per-line syntax highlight).
-//
-// Outer WeakMap keyed by theme so palette swaps drop stale baked-in colors
-// without code intervention. Inner Map is LRU-bounded; key folds `compact`
-// in so the two layout modes don't poison each other.
+// Cross-instance parsed-children cache: useMemo's per-instance cache dies
+// on remount, so virtualization re-parses every row that scrolls back into
+// view. Theme-keyed WeakMap drops stale palettes; inner Map is LRU-bounded.
 const MD_CACHE_LIMIT = 512
 const mdCache = new WeakMap<Theme, Map<string, ReactNode[]>>()
 
 const cacheBucket = (t: Theme) => {
-  let b = mdCache.get(t)
+  const b = mdCache.get(t)
 
-  if (!b) {
-    b = new Map()
-    mdCache.set(t, b)
+  if (b) {
+    return b
   }
 
-  return b
+  const fresh = new Map<string, ReactNode[]>()
+  mdCache.set(t, fresh)
+
+  return fresh
 }
 
 const cacheGet = (b: Map<string, ReactNode[]>, key: string) => {