fix: address pr-bug-scan validated finding from #4731

C1: restore-side git-status signature now applies the same treeMode short-circuit as save-side, so branch/commit caches restore. C2: editable-diff modified-model key/component key no longer embed dc.m

src/renderer/src/components/editor/CombinedDiffViewer.tsx

@@ -441,11 +441,19 @@ export default function CombinedDiffViewer({
   // find their place again.
   useEffect(() => {
     const cached = combinedDiffViewStateCache.get(viewStateKey)
+    // Why: the save-side signature is '' for branch/commit modes (only the
+    // uncommitted tree tracks git status), so the restore-side recompute must
+    // apply the same treeMode short-circuit. Otherwise '' can never equal the
+    // recomputed '[]'/'[...]', and branch/commit combined diffs would always
+    // discard their cached sections and re-enter Loading on every remount.
+    const cachedGitStatusSignature =
+      cached && treeMode === 'uncommitted'
+        ? buildCombinedGitStatusSignature(cached.sections, gitStatusEntries)
+        : ''
     const canRestoreCachedSections =
       cached &&
       cached.entrySignature === entrySignature &&
-      (cached.gitStatusSignature ?? '') ===
-        buildCombinedGitStatusSignature(cached.sections, gitStatusEntries) &&
+      (cached.gitStatusSignature ?? '') === cachedGitStatusSignature &&
       (cached.sections.length > 0 || entries.length === 0)
     if (canRestoreCachedSections && cached) {
       const collapsedPreference = combinedDiffCollapsedPreference
@@ -493,7 +501,7 @@ export default function CombinedDiffViewer({
     loadSchedulerRef.current.reset()
     generationRef.current += 1
     setGeneration((prev) => prev + 1)
-  }, [entries, entrySignature, file.diffSource, gitStatusEntries, viewStateKey])
+  }, [entries, entrySignature, file.diffSource, gitStatusEntries, treeMode, viewStateKey])
 
   const loadSectionNow = useCallback(
     async (index: number) => {

src/renderer/src/components/editor/EditorContent.tsx

@@ -851,10 +851,24 @@ export function EditorContent({
   // edit-buffer text, so editable unstaged diffs keep their undo stack.
   const diffReloadNonce = activeFile.diffContentReloadNonce ?? 0
   const originalModelKey = `${diffViewStateKey}:original:${getDiffContentSignature(dc.originalContent)}`
-  const modifiedModelKey = `${diffViewStateKey}:modified:${getDiffContentSignature(dc.modifiedContent)}:${diffReloadNonce}`
+  // Why: for editable diffs the modified side is the working tree the user is
+  // editing. Saving rewrites dc.modifiedContent (via the FILE_SAVED handler),
+  // so embedding its signature in the modified-model identity / component key
+  // would remount Monaco on every save and wipe the undo stack the user just
+  // built. Rotate the modified side on the explicit reload nonce instead; a
+  // kept modified model still repaints refreshed git blobs through the
+  // `modified` prop's undo-preserving executeEdits. Non-editable diffs have no
+  // undo to lose, so they keep rotating on the content signature.
+  const modifiedContentSignature = getDiffContentSignature(dc.modifiedContent)
+  const modifiedModelKey = isEditable
+    ? `${diffViewStateKey}:modified:${diffReloadNonce}`
+    : `${diffViewStateKey}:modified:${modifiedContentSignature}:${diffReloadNonce}`
+  const diffViewerKey = isEditable
+    ? `${viewStateScopeId}:${diffReloadNonce}`
+    : `${viewStateScopeId}:${diffReloadNonce}:${modifiedContentSignature}`
   return (
     <DiffViewer
-      key={`${viewStateScopeId}:${diffReloadNonce}:${getDiffContentSignature(dc.modifiedContent)}`}
+      key={diffViewerKey}
       modelKey={diffViewStateKey}
       originalModelKey={originalModelKey}
       modifiedModelKey={modifiedModelKey}