fix(diffs): bound the selection-restore retry window

Adversarial review (Opus) showed the wall-clock deadline re-armed on Pierre's
'update' phase, which fires on every render, so a row receiving periodic renders
could push it forward indefinitely -- the 2s bound was not a bound.

Keep the extension (convergence genuinely needs a later Pierre render; gating to
'mount' alone regresses restore) but add a hard ceiling from mount, past which no
further extension is granted. A row that renders forever without converging can
no longer spin forever.

Also moves the measured-height discard below the stale-payload skip: a rejected
payload was resizing the row the user is typing in.

src/renderer/src/components/editor/combined-diff/load-sections/use-combined-diff-section-loader.ts

@@ -151,10 +151,6 @@ export function useCombinedDiffSectionLoader({
       ) {
         return
       }
-      if (wasShowingContent) {
-        // Why: content really changed, so the old Monaco height no longer describes this row.
-        setSectionHeights((prev) => removeDiffSectionMeasuredHeight(prev, index))
-      }
       // `dirty` flips back to false once a save is acknowledged, so it cannot tell a stale payload
       // from a fresh one. If the draft moved while this fetch was in flight, only commit when the
       // payload actually agrees with that draft — otherwise this reverts the user's saved text on
@@ -163,6 +159,11 @@ export function useCombinedDiffSectionLoader({
       if (liveDraft !== draftAtFetchStart && storedContent.modifiedContent !== liveDraft) {
         return
       }
+      if (wasShowingContent) {
+        // Why: content really changed, so the old measured height no longer describes this row.
+        // Must follow the skip above, or a rejected payload resizes the row being typed in.
+        setSectionHeights((prev) => removeDiffSectionMeasuredHeight(prev, index))
+      }
       setSections((prev) => {
         return prev.map((s, i) =>
           i === index && !s.dirty

src/renderer/src/components/editor/pierre-diff/use-pierre-diff-native-view.ts

@@ -14,7 +14,12 @@ import {
 // The editor reasserts its own selection on attach, which can land well after ours. Budget by
 // wall clock, not frames: under load a frame count expires long before the editor settles.
 // User interaction still cancels the pending restore, so this only bounds the quiet case.
+// The editor reasserts its own selection well after ours, and convergence needs a later Pierre
+// render, so the window extends on each render while a restore is still pending. RESTORE_CEILING
+// is the hard bound: past it no further extension is granted, so a row that renders forever
+// without converging cannot spin forever. User interaction cancels the restore sooner still.
 const RESTORE_DEADLINE_MS = 2_000
+const RESTORE_CEILING_MS = 15_000
 
 export function usePierreDiffNativeView(
   key: string | undefined,
@@ -34,6 +39,7 @@ export function usePierreDiffNativeView(
   const frame = useRef<number | null>(null)
   // Armed on attach; 0 until then so a stale ref can never keep a restore alive.
   const deadline = useRef(0)
+  const ceiling = useRef(0)
   const lastSnapshot = useRef<PierreNativeViewState | undefined>(undefined)
   const schedule = useCallback(() => {
     if (frame.current !== null || !pending.current || Date.now() > deadline.current) {
@@ -103,7 +109,9 @@ export function usePierreDiffNativeView(
     })
   }, [editorRef])
   useLayoutEffect(() => {
-    deadline.current = Date.now() + RESTORE_DEADLINE_MS
+    const now = Date.now()
+    ceiling.current = now + RESTORE_CEILING_MS
+    deadline.current = now + RESTORE_DEADLINE_MS
     schedule()
   }, [activeGroupId, schedule])
   useLayoutEffect(() => {
@@ -174,8 +182,14 @@ export function usePierreDiffNativeView(
     (host: HTMLElement, phase: PostRenderPhase, instance: PierreDiffInstance) => {
       if (phase !== 'unmount') {
         view.current = { host, instance }
-        // Re-arm on attach: the remount is the point a restore becomes possible.
-        deadline.current = Date.now() + RESTORE_DEADLINE_MS
+        const now = Date.now()
+        if (phase === 'mount') {
+          ceiling.current = now + RESTORE_CEILING_MS
+        }
+        // Extend while a restore is still pending, but never past the ceiling.
+        if (pending.current && now < ceiling.current) {
+          deadline.current = Math.min(now + RESTORE_DEADLINE_MS, ceiling.current)
+        }
         schedule()
       }
     },