fix(diffs): start the restore ceiling at view attach, not component mount

Two P1s from adversarial review (Opus), both introduced by the previous commit.

The ceiling was armed in the mount-time layout effect, but the deadline can only
be extended at attach while `now < ceiling`. A large or remote diff whose first
postRender lands after the ceiling had already elapsed got no window at all, so
the restore never ran once -- scroll, selection and setDeletedTextSelectionActive
were silently dropped. This repo's own spec allows 20s for the first diff line to
appear, so renders past a mount-anchored 15s ceiling are expected. Arm the
ceiling at first attach instead, and clamp every deadline re-arm to it.

The self-heal also cleared `loadedIndices` unconditionally. requestSectionReload
already clears it when it proceeds and refuses while the row is dirty -- which is
exactly the state that triggers the skip -- so the only observable effect was to
strand the index unscheduled, making the next virtualizer scroll-in refetch a row
the user is typing in, over git, on SSH.

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

@@ -161,9 +161,10 @@ export function useCombinedDiffSectionLoader({
         storedContent.modifiedContent === liveDraft &&
         storedContent.originalContent === liveSection?.originalContent
       if (liveDraft !== draftAtFetchStart && !payloadMatchesLive) {
-        // Why: this index is already marked loaded, so drop that mark and re-drive the fetch —
-        // otherwise a rejected payload pins the section stale with no path back on its own.
-        loadedIndicesRef.current.delete(index)
+        // Why: re-drive the fetch so a rejected payload does not pin the section stale. Do not
+        // clear `loadedIndices` here — requestSectionReload clears it itself when it proceeds,
+        // and refuses while the row is dirty. Clearing unconditionally would strand the index
+        // unscheduled, making the next virtualizer scroll-in refetch a row being typed in.
         requestSectionReloadRef.current(index)
         return
       }

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

@@ -109,13 +109,13 @@ export function usePierreDiffNativeView(
     })
   }, [editorRef])
   useLayoutEffect(() => {
+    // Why: no window is granted here. The ceiling starts at the first view attach, not at
+    // component mount — a large or remote diff can attach many seconds later, and a window
+    // measured from mount would already be spent before the view ever exists.
     const now = Date.now()
-    // Arm once: the ceiling bounds this restore, not each mount. Re-arming per mount (or per
-    // activeGroupId change) would let an unmount/mount cycle extend it forever.
-    if (ceiling.current === 0) {
-      ceiling.current = now + RESTORE_CEILING_MS
+    if (ceiling.current !== 0 && now < ceiling.current) {
+      deadline.current = Math.min(now + RESTORE_DEADLINE_MS, ceiling.current)
     }
-    deadline.current = now + RESTORE_DEADLINE_MS
     schedule()
   }, [activeGroupId, schedule])
   useLayoutEffect(() => {
@@ -193,9 +193,13 @@ export function usePierreDiffNativeView(
       }
       {
         view.current = { host, instance }
-        // Extend while a restore is still pending, but never past the ceiling, and never re-arm
-        // the ceiling here: FileDiff emits 'mount' on every remount cycle.
+        // Start the ceiling at the first attach, then extend while a restore is still pending but
+        // never past it. FileDiff emits 'mount' on every remount cycle, so the ceiling is armed
+        // once and never re-armed here.
         const now = Date.now()
+        if (ceiling.current === 0) {
+          ceiling.current = now + RESTORE_CEILING_MS
+        }
         if (pending.current && now < ceiling.current) {
           deadline.current = Math.min(now + RESTORE_DEADLINE_MS, ceiling.current)
         }