refactor(tui): /clean pass on memory + resize helpers

KISS/DRY sweep — drops ~90 LOC with no behavior change.

- circularBuffer: drop unused pushAll/toArray/size; fold toArray into drain
- gracefulExit: inline Cleanup type + failsafe const; signal→code as a
  record instead of nested ternary; drop dead .catch on Promise.allSettled;
  drop unused forceExit
- memory: inline heapDumpRoot() + writeSnapshot() (single-use); collapse
  the two fd/smaps try/catch blocks behind one `swallow` helper; build
  potentialLeaks functionally (array+filter) instead of imperative
  push-chain; UNITS at file bottom
- memoryMonitor: inline DEFAULTS; drop unused onSnapshot; collapse
  dumpedHigh/dumpedCritical bools to a single Set; single callback
  dispatch line instead of duplicated if-chains
- entry.tsx: factor `dumpNotice` formatter (used twice by onHigh +
  onCritical)
- useMainApp resize debounce: drop redundant `if (timer)` guards
  (clearTimeout(undefined) is a no-op); init as undefined not null
- useVirtualHistory: trim wall-of-text comment to one-line intent; hoist
  `const n = items.length`; split comma-declared lets; remove the
  `;[start, end] = frozenRange` destructure in favor of direct Math.min
  clamps; hoist `hi` init in upperBound for consistency

Validation: tsc clean (both configs), eslint clean on touched files,
vitest 102/102, build produces shebang-preserved dist/entry.js,
performHeapDump smoke-test still writes valid snapshot + diagnostics.

ui-tui/src/hooks/useVirtualHistory.ts

@@ -18,11 +18,12 @@ const QUANTUM = OVERSCAN >> 1
 const FREEZE_RENDERS = 2
 
 const upperBound = (arr: number[], target: number) => {
-  let lo = 0,
-    hi = arr.length
+  let lo = 0
+  let hi = arr.length
 
   while (lo < hi) {
     const mid = (lo + hi) >> 1
+
     arr[mid]! <= target ? (lo = mid + 1) : (hi = mid)
   }
 
@@ -42,16 +43,11 @@ export function useVirtualHistory(
   const [hasScrollRef, setHasScrollRef] = useState(false)
   const metrics = useRef({ sticky: true, top: 0, vp: 0 })
 
-  // Resize handling — scale cached heights by oldCols/newCols so post-resize
-  // offsets stay roughly aligned with (still-unknown) real Yoga heights.
-  // Clearing the cache instead would force a pessimistic back-walk that mounts
-  // ~190 rows at once (viewport+overscan at 1-row estimate), each a fresh
-  // marked.lexer + syntax highlight = ~3ms; ~600ms React commit block. Freeze
-  // the mount range for FREEZE_RENDERS so warm useMemo results survive while
-  // the layout effect writes post-resize real heights back into cache.
-  // skipMeasurement prevents that first post-resize useLayoutEffect from
-  // poisoning the cache with pre-resize Yoga values (Yoga's stored heights
-  // are from the frame BEFORE this render's calculateLayout with new width).
+  // Width change: scale cached heights (not clear — clearing forces a
+  // pessimistic back-walk mounting ~190 rows at once, each a fresh
+  // marked.lexer + syntax highlight ≈ 3ms). Freeze mount range for 2
+  // renders so warm memos survive; skip one measurement so useLayoutEffect
+  // doesn't poison the scaled cache with pre-resize Yoga heights.
   const prevColumns = useRef(columns)
   const skipMeasurement = useRef(false)
   const prevRange = useRef<null | readonly [number, number]>(null)
@@ -122,34 +118,32 @@ export function useVirtualHistory(
     return out
   }, [estimate, items, ver])
 
-  const total = offsets[items.length] ?? 0
+  const n = items.length
+  const total = offsets[n] ?? 0
   const top = Math.max(0, scrollRef.current?.getScrollTop() ?? 0)
   const vp = Math.max(0, scrollRef.current?.getViewportHeight() ?? 0)
   const sticky = scrollRef.current?.isSticky() ?? true
 
   const frozenRange = freezeRenders.current > 0 ? prevRange.current : null
 
-  let start = 0,
-    end = items.length
+  let start = 0
+  let end = n
 
   if (frozenRange) {
-    // Columns just changed. Reuse the pre-resize mount range so already-mounted
-    // MessageRows keep their warm memos (marked.lexer, syntax highlight). Clamp
-    // to n in case messages were removed (/clear, compaction) mid-freeze.
-    ;[start, end] = frozenRange
-    start = Math.min(start, items.length)
-    end = Math.min(end, items.length)
-  } else if (items.length > 0) {
+    // Clamp in case items shrank (/clear, compaction) mid-freeze.
+    start = Math.min(frozenRange[0], n)
+    end = Math.min(frozenRange[1], n)
+  } else if (n > 0) {
     if (vp <= 0) {
-      start = Math.max(0, items.length - coldStartCount)
+      start = Math.max(0, n - coldStartCount)
     } else {
-      start = Math.max(0, Math.min(items.length - 1, upperBound(offsets, Math.max(0, top - overscan)) - 1))
-      end = Math.max(start + 1, Math.min(items.length, upperBound(offsets, top + vp + overscan)))
+      start = Math.max(0, Math.min(n - 1, upperBound(offsets, Math.max(0, top - overscan)) - 1))
+      end = Math.max(start + 1, Math.min(n, upperBound(offsets, top + vp + overscan)))
     }
   }
 
   if (end - start > maxMounted) {
-    sticky ? (start = Math.max(0, end - maxMounted)) : (end = Math.min(items.length, start + maxMounted))
+    sticky ? (start = Math.max(0, end - maxMounted)) : (end = Math.min(n, start + maxMounted))
   }
 
   if (freezeRenders.current > 0) {
@@ -173,9 +167,6 @@ export function useVirtualHistory(
     let dirty = false
 
     if (skipMeasurement.current) {
-      // First render after a column change — Yoga heights still reflect the
-      // pre-resize layout. Writing them into cache would overwrite the scaled
-      // estimates with stale pre-resize values. Next render's Yoga is correct.
       skipMeasurement.current = false
     } else {
       for (let i = start; i < end; i++) {