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/entry-exports.ts

@@ -1,12 +1,7 @@
 export { default as useStderr } from './hooks/use-stderr.js'
 export { default as useStdout } from './hooks/use-stdout.js'
 export { Ansi } from './ink/Ansi.js'
-export {
-  evictInkCaches,
-  type EvictLevel,
-  type InkCacheSizes,
-  inkCacheSizes
-} from './ink/cache-eviction.js'
+export { evictInkCaches, type EvictLevel, type InkCacheSizes, inkCacheSizes } from './ink/cache-eviction.js'
 export { AlternateScreen } from './ink/components/AlternateScreen.js'
 export { default as Box } from './ink/components/Box.js'
 export { default as Link } from './ink/components/Link.js'
@@ -26,13 +21,9 @@ export { useTabStatus } from './ink/hooks/use-tab-status.js'
 export { useTerminalFocus } from './ink/hooks/use-terminal-focus.js'
 export { useTerminalTitle } from './ink/hooks/use-terminal-title.js'
 export { useTerminalViewport } from './ink/hooks/use-terminal-viewport.js'
-export { isXtermJs } from './ink/terminal.js'
 export { default as measureElement } from './ink/measure-element.js'
-export {
-  resetScrollFastPathStats,
-  scrollFastPathStats,
-  type ScrollFastPathStats
-} from './ink/render-node-to-output.js'
+export { resetScrollFastPathStats, scrollFastPathStats, type ScrollFastPathStats } from './ink/render-node-to-output.js'
 export { createRoot, default as render, renderSync } from './ink/root.js'
 export { stringWidth } from './ink/stringWidth.js'
+export { isXtermJs } from './ink/terminal.js'
 export { default as TextInput, UncontrolledTextInput } from 'ink-text-input'

ui-tui/packages/hermes-ink/src/ink/cache-eviction.ts

@@ -9,12 +9,12 @@
 // (not session-keyed), so cross-session sharing is normally beneficial —
 // only evict when memory tightens or when the user explicitly resets.
 
+import { evictSliceCache, sliceCacheSize } from '../utils/sliceAnsi.js'
+
 import { evictLineWidthCache, lineWidthCacheSize } from './line-width-cache.js'
 import { evictWidthCache, widthCacheSize } from './stringWidth.js'
 import { evictWrapCache, wrapCacheSize } from './wrap-text.js'
 
-import { evictSliceCache, sliceCacheSize } from '../utils/sliceAnsi.js'
-
 export interface InkCacheSizes {
   lineWidth: number
   slice: number

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

@@ -979,15 +979,13 @@ export default class Ink {
     }
 
     const tWrite = performance.now()
+
     // Capture any stale pending write BEFORE starting this frame's write —
     // if the callback already fired, pendingWriteStart is null and lastDrainMs
     // already reflects the previous frame's drain.  If it hasn't fired, we
     // report "still pending" via a non-zero duration based on now-then so
     // backpressure shows up even if Node never flushes this session.
-    const staleDrain =
-      this.pendingWriteStart !== null
-        ? performance.now() - this.pendingWriteStart
-        : this.lastDrainMs
+    const staleDrain = this.pendingWriteStart !== null ? performance.now() - this.pendingWriteStart : this.lastDrainMs
 
     const prevFrameDrainMs = Math.round(staleDrain * 100) / 100
     this.lastDrainMs = 0
@@ -1016,6 +1014,7 @@ export default class Ink {
           }
         : undefined
     )
+
     const writeMs = performance.now() - tWrite
 
     // Update blit safety for the NEXT frame. The frame just rendered

ui-tui/packages/hermes-ink/src/ink/line-width-cache.ts

@@ -1,3 +1,4 @@
+import { lruEvict } from './lru.js'
 import { stringWidth } from './stringWidth.js'
 
 // During streaming, text grows but completed lines are immutable.
@@ -13,6 +14,7 @@ export function lineWidth(line: string): number {
   if (cached !== undefined) {
     cache.delete(line)
     cache.set(line, cached)
+
     return cached
   }
 
@@ -32,14 +34,5 @@ export function lineWidthCacheSize(): number {
 }
 
 export function evictLineWidthCache(keepRatio = 0): void {
-  if (keepRatio <= 0) {
-    cache.clear()
-    return
-  }
-
-  const target = Math.floor(cache.size * keepRatio)
-
-  while (cache.size > target) {
-    cache.delete(cache.keys().next().value!)
-  }
+  lruEvict(cache, keepRatio)
 }

ui-tui/packages/hermes-ink/src/ink/lru.ts

@@ -0,0 +1,14 @@
+// Shared eviction for the hot Ink LRU caches (widthCache, wrapCache,
+// sliceCache, lineWidthCache). Hot-path touch-on-read stays inlined per
+// cache — only the bulk eviction is factored here.
+export function lruEvict<K, V>(cache: Map<K, V>, keepRatio: number): void {
+  if (keepRatio <= 0) {
+    return cache.clear()
+  }
+
+  const target = Math.floor(cache.size * keepRatio)
+
+  while (cache.size > target) {
+    cache.delete(cache.keys().next().value!)
+  }
+}

ui-tui/packages/hermes-ink/src/ink/output.ts

@@ -467,15 +467,15 @@ export default class Output {
 
             if (clipHorizontally) {
               lines = lines.map(line => {
-                const startsBefore = x < clip.x1!
                 const width = stringWidth(line)
+                const startsBefore = x < clip.x1!
                 const endsAfter = x + width > clip.x2!
 
                 // Fast path: line fits entirely within the clip box — skip
-                // the tokenize/slice. This is the common case for transcript
-                // text where containers are wider than the rendered content.
-                // CPU profile (Apr 2026) showed sliceAnsi at 18% total time;
-                // most calls were no-op slices like (line, 0, width).
+                // tokenize/slice. Common case for transcript text where
+                // containers are wider than rendered content. CPU profile
+                // (Apr 2026): sliceAnsi at 18% total during scroll, mostly
+                // no-op (line, 0, width) slices.
                 if (!startsBefore && !endsAfter) {
                   return line
                 }

ui-tui/packages/hermes-ink/src/ink/render-node-to-output.ts

@@ -111,7 +111,6 @@ export function resetScrollFastPathStats(): void {
   scrollFastPathStats.lastPrevHeight = undefined
 }
 
-
 export function getScrollHint(): ScrollHint | null {
   return scrollHint
 }

ui-tui/packages/hermes-ink/src/ink/stringWidth.ts

@@ -4,6 +4,8 @@ import stripAnsi from 'strip-ansi'
 
 import { getGraphemeSegmenter } from '../utils/intl.js'
 
+import { lruEvict } from './lru.js'
+
 const EMOJI_REGEX = emojiRegex()
 
 /**
@@ -299,6 +301,7 @@ export const stringWidth: (str: string) => number = str => {
 
       if (code >= 127 || code === 0x1b) {
         asciiOnly = false
+
         break
       }
     }
@@ -334,14 +337,5 @@ export function widthCacheSize(): number {
 }
 
 export function evictWidthCache(keepRatio = 0): void {
-  if (keepRatio <= 0) {
-    widthCache.clear()
-    return
-  }
-
-  const target = Math.floor(widthCache.size * keepRatio)
-
-  while (widthCache.size > target) {
-    widthCache.delete(widthCache.keys().next().value!)
-  }
+  lruEvict(widthCache, keepRatio)
 }

ui-tui/packages/hermes-ink/src/ink/terminal.ts

@@ -289,9 +289,7 @@ export function writeDiffToTerminal(
   // The 2-arg form attaches a drain callback that fires once the chunk
   // is actually flushed to the OS socket/pipe — giving us end-to-end
   // drain timing, not just "queued in Node".
-  const wrote = onDrain
-    ? terminal.stdout.write(buffer, () => onDrain())
-    : terminal.stdout.write(buffer)
+  const wrote = onDrain ? terminal.stdout.write(buffer, () => onDrain()) : terminal.stdout.write(buffer)
 
   return { bytes: Buffer.byteLength(buffer, 'utf8'), backpressure: !wrote }
 }

ui-tui/packages/hermes-ink/src/ink/wrap-text.ts

@@ -1,5 +1,6 @@
 import sliceAnsi from '../utils/sliceAnsi.js'
 
+import { lruEvict } from './lru.js'
 import { stringWidth } from './stringWidth.js'
 import type { Styles } from './styles.js'
 import { wrapAnsi } from './wrapAnsi.js'
@@ -113,14 +114,5 @@ export function wrapCacheSize(): number {
 }
 
 export function evictWrapCache(keepRatio = 0): void {
-  if (keepRatio <= 0) {
-    wrapCache.clear()
-    return
-  }
-
-  const target = Math.floor(wrapCache.size * keepRatio)
-
-  while (wrapCache.size > target) {
-    wrapCache.delete(wrapCache.keys().next().value!)
-  }
+  lruEvict(wrapCache, keepRatio)
 }

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 {