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/app/useSessionLifecycle.ts

@@ -29,10 +29,11 @@ export const writeActiveSessionFile = (sessionId: null | string, file = process.
     return
   }
 
+  // Best-effort shell-epilogue hint; never break live session changes.
   try {
     writeFileSync(file, JSON.stringify({ session_id: sessionId }), { mode: 0o600 })
   } catch {
-    // Best-effort shell epilogue hint only; never break live session changes.
+    /* best-effort */
   }
 }
 
@@ -98,8 +99,8 @@ export function useSessionLifecycle(opts: UseSessionLifecycleOptions) {
     setLastUserMsg('')
     setStickyPrompt('')
     composerActions.setPasteSnips([])
-    // Half-prune Ink content caches: new session has new keys, but a partial
-    // warm pool helps if the user resumes back to the prior session.
+    // Half-prune: new session has new keys, but keep a warm pool in case
+    // the user resumes back to the prior session.
     evictInkCaches('half')
   }, [composerActions, setHistoryItems, setLastUserMsg, setStickyPrompt, setVoiceProcessing, setVoiceRecording])