fix(diff): keep the load registry live across a StrictMode effect replay

StrictMode runs setup -> cleanup -> setup with no render between the two setups, so the
render-time write alone left the flag false for the life of the replayed mount and every
later reload silently bailed. Write it in both places: render covers the window where child
effects run before this parent's, the effect covers the replayed cleanup.

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

@@ -59,8 +59,9 @@ export function useCombinedDiffSectionLoadRegistry(
   loadSchedulerRef.current ??= createCombinedDiffLoadScheduler({
     loadSection: (index) => loadSectionRef.current(index)
   })
-  // Why here and not in the effect below: child effects run before this parent's, so StrictMode's
-  // replayed mount would leave a window where the ref reads false while the viewer is live.
+  // Why in render AND in the effect below: child effects run before this parent's, so a
+  // render-only write covers that window; StrictMode replays setup -> cleanup -> setup with no
+  // render in between, so an effect-only write is needed to survive the replayed cleanup.
   registryLiveRef.current = true
 
   useEffect(() => {
@@ -68,6 +69,7 @@ export function useCombinedDiffSectionLoadRegistry(
     const scheduler = loadSchedulerRef.current
     const reloadTimers = reloadTimersRef.current
     scheduler.reset()
+    registryLiveRef.current = true
     return () => {
       registryLiveRef.current = false
       clearPendingSectionReloadTimers(reloadTimers)

src/renderer/src/components/editor/combined-diff/load-sections/use-combined-diff-section-retry.test.tsx

@@ -1,7 +1,7 @@
 // @vitest-environment happy-dom
 import { act, renderHook } from '@testing-library/react'
 import { beforeEach, describe, expect, it, vi } from 'vitest'
-import { useRef } from 'react'
+import { StrictMode, useRef } from 'react'
 import type { DiffSection } from '../../diff-section-types'
 import { useCombinedDiffSectionLoadRegistry } from './combined-diff-section-load-registry'
 import { useCombinedDiffSectionRetry } from './use-combined-diff-section-retry'
@@ -77,3 +77,25 @@ describe('deferred section reloads', () => {
     expect(invalidate).not.toHaveBeenCalled()
   })
 })
+
+it('still reloads after StrictMode replays the registry effect', () => {
+  // Why: StrictMode runs setup -> cleanup -> setup with no render between the two setups, so a
+  // render-only live flag stays false for the life of the replayed mount.
+  const view = renderHook(
+    () => {
+      const sectionsRef = useRef([section()])
+      const registry = useCombinedDiffSectionLoadRegistry(sectionsRef)
+      const actions = useCombinedDiffSectionRetry({
+        invalidateViewStateCache: invalidate,
+        registry,
+        setSectionHeights: vi.fn(),
+        setSections: vi.fn()
+      })
+      registry.renderedIndicesRef.current.add(0)
+      return actions
+    },
+    { wrapper: StrictMode }
+  )
+  act(() => view.result.current.requestSectionReload(0))
+  expect(invalidate).toHaveBeenCalled()
+})