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/lib/virtualHeights.ts

@@ -14,18 +14,18 @@ export const hashText = (text: string) => {
 
 export const messageHeightKey = (msg: Msg) => {
   const todoSig = msg.todos?.map(t => `${t.status}:${t.content}`).join('\u0001') ?? ''
+
   const panelSig =
     msg.panelData?.sections
       .map(s => `${s.title ?? ''}:${s.text?.length ?? 0}:${s.items?.length ?? 0}:${s.rows?.length ?? 0}`)
       .join('\u0001') ?? ''
+
   const introSig = msg.kind === 'intro' ? (msg.info?.version ?? '') : ''
 
   return [
     msg.role,
     msg.kind ?? '',
-    hashText(
-      [msg.text, msg.thinking ?? '', msg.tools?.join('\n') ?? '', todoSig, panelSig, introSig].join('\0')
-    )
+    hashText([msg.text, msg.thinking ?? '', msg.tools?.join('\n') ?? '', todoSig, panelSig, introSig].join('\0'))
   ].join(':')
 }
 
@@ -68,11 +68,9 @@ export const estimatedMsgHeight = (
     h += (msg.tools?.length ?? 0) + wrappedLines(msg.thinking ?? '', bodyWidth)
   }
 
-  if (msg.role === 'user' || msg.kind === 'slash' || msg.kind === 'diff') {
-    h++
-  }
-
   if (msg.role === 'user' || msg.kind === 'diff') {
+    h += 2
+  } else if (msg.kind === 'slash') {
     h++
   }