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/packages/hermes-ink/src/utils/sliceAnsi.ts

@@ -1,5 +1,6 @@
 import { type AnsiCode, ansiCodesToString, reduceAnsiCodes, tokenize, undoAnsiCodes } from '@alcalzone/ansi-tokenize'
 
+import { lruEvict } from '../ink/lru.js'
 import { stringWidth } from '../ink/stringWidth.js'
 
 function isEndCode(code: AnsiCode): boolean {
@@ -19,7 +20,9 @@ const sliceCache = new Map<string, string>()
 const SLICE_CACHE_LIMIT = 4096
 
 export default function sliceAnsi(str: string, start: number, end?: number): string {
-  if (!str) return ''
+  if (!str) {
+    return ''
+  }
 
   // Hot-path: only cache when end is defined (the Output.get() use-case).
   if (end !== undefined) {
@@ -29,6 +32,7 @@ export default function sliceAnsi(str: string, start: number, end?: number): str
     if (cached !== undefined) {
       sliceCache.delete(key)
       sliceCache.set(key, cached)
+
       return cached
     }
 
@@ -39,6 +43,7 @@ export default function sliceAnsi(str: string, start: number, end?: number): str
     }
 
     sliceCache.set(key, result)
+
     return result
   }
 
@@ -50,16 +55,7 @@ export function sliceCacheSize(): number {
 }
 
 export function evictSliceCache(keepRatio = 0): void {
-  if (keepRatio <= 0) {
-    sliceCache.clear()
-    return
-  }
-
-  const target = Math.floor(sliceCache.size * keepRatio)
-
-  while (sliceCache.size > target) {
-    sliceCache.delete(sliceCache.keys().next().value!)
-  }
+  lruEvict(sliceCache, keepRatio)
 }
 
 function computeSlice(str: string, start: number, end?: number): string {