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/config/env.ts

@@ -1,19 +1,15 @@
+const truthy = (v?: string) => /^(?:1|true|yes|on)$/i.test((v ?? '').trim())
+
 export const STARTUP_RESUME_ID = (process.env.HERMES_TUI_RESUME ?? '').trim()
-export const MOUSE_TRACKING = !/^(?:1|true|yes|on)$/i.test((process.env.HERMES_TUI_DISABLE_MOUSE ?? '').trim())
-export const NO_CONFIRM_DESTRUCTIVE = /^(?:1|true|yes|on)$/i.test((process.env.HERMES_TUI_NO_CONFIRM ?? '').trim())
-// Inline mode: skip the alt-screen wrapper.  The TUI renders into the
-// primary buffer so the terminal's native scrollback captures whatever
-// scrolls off the top.  Wheel + PageUp are then handled by the host
-// terminal, not by our virtual-scroll logic.  The live composer/progress
-// area still pins to the bottom via Ink's normal flow.
-//
-// This is an experiment gate — the full "inline layout" (plain-text
-// transcript with composer pinned below) is a bigger change; the env var
-// here just disables AlternateScreen so we can measure whether native
-// scrolling beats our virtualization on the same pipeline.
-export const INLINE_MODE = /^(?:1|true|yes|on)$/i.test((process.env.HERMES_TUI_INLINE ?? '').trim())
-// Show a small FPS counter overlay in the bottom-right corner. Fed by
-// ink's onFrame callback (so it's the REAL render rate, not a synthetic
-// timer).  Useful during scroll-perf tuning to watch behavior in real
-// time instead of running a separate profile harness.
-export const SHOW_FPS = /^(?:1|true|yes|on)$/i.test((process.env.HERMES_TUI_FPS ?? '').trim())
+export const MOUSE_TRACKING = !truthy(process.env.HERMES_TUI_DISABLE_MOUSE)
+export const NO_CONFIRM_DESTRUCTIVE = truthy(process.env.HERMES_TUI_NO_CONFIRM)
+
+// Skip AlternateScreen — TUI renders into the primary buffer so the host
+// terminal's native scrollback captures whatever scrolls off the top.
+// Experiment gate: lets us measure native scroll vs our virtualization on
+// the same pipeline.
+export const INLINE_MODE = truthy(process.env.HERMES_TUI_INLINE)
+
+// Live FPS counter overlay, fed by ink's onFrame (real render rate, not a
+// synthetic timer).
+export const SHOW_FPS = truthy(process.env.HERMES_TUI_FPS)