test: add test coverage for duplicate-path snapshot remapping

- Add unit test verifying that duplicate-path snapshots do not remap
  to a retained fallback area.
- Robustify E2E large diff freeze repro test by ensuring interval
  timers are always cleared in a finally block.
- Standardize path utilities in large diff fixtures to ensure cross-platform
  compatibility.

src/renderer/src/components/editor/combined-diff-entries.test.ts

@@ -145,6 +145,18 @@ describe('resolveCombinedUncommittedSnapshotEntries', () => {
     )
   })
 
+  it('does not remap duplicate-path snapshots to a retained fallback area', () => {
+    const snapshotEntries: GitStatusEntry[] = [
+      { path: 'src/file.ts', status: 'modified', area: 'staged', added: 4 },
+      { path: 'src/file.ts', status: 'modified', area: 'unstaged', added: 2 }
+    ]
+    const retained: GitStatusEntry[] = [{ path: 'src/file.ts', status: 'modified', area: 'staged' }]
+
+    expect(resolveCombinedUncommittedSnapshotEntries(snapshotEntries, [], retained)).toEqual([
+      { path: 'src/file.ts', status: 'modified', area: 'staged', added: 4 }
+    ])
+  })
+
   it('does not let a retained stale area duplicate an original target area', () => {
     const snapshotEntries: GitStatusEntry[] = [
       { path: 'src/file.ts', status: 'modified', area: 'unstaged', added: 2 },

tests/e2e/large-diff-freeze-repro.spec.ts

@@ -184,6 +184,8 @@ test.describe('Large diff freeze repro', () => {
             throw new Error(`staged locale fixture missing entries: ${missing.join(', ')}`)
           }
 
+          // Why: reproduce stale snapshot behavior by opening combined diffs
+          // as "unstaged" using entries captured from the staged status snapshot.
           const staleUnstagedEntries = entries.map((entry) => ({ ...entry, area: 'unstaged' }))
           const intervalMs = 50
           const samples: number[] = []
@@ -202,17 +204,22 @@ test.describe('Large diff freeze repro', () => {
 
           let editorCount = 0
           let fallbackCount = 0
-          while (performance.now() - startedAt < 30_000) {
-            await new Promise((resolve) => window.setTimeout(resolve, 50))
-            editorCount = document.querySelectorAll('.monaco-diff-editor').length
-            fallbackCount = document.querySelectorAll('[data-testid="large-diff-fallback"]').length
-            if (editorCount + fallbackCount >= Math.min(entries.length, 5)) {
-              await new Promise((resolve) => window.setTimeout(resolve, 1_000))
-              break
+          try {
+            while (performance.now() - startedAt < 30_000) {
+              await new Promise((resolve) => window.setTimeout(resolve, 50))
+              editorCount = document.querySelectorAll('.monaco-diff-editor').length
+              fallbackCount = document.querySelectorAll(
+                '[data-testid="large-diff-fallback"]'
+              ).length
+              if (editorCount + fallbackCount >= Math.min(entries.length, 5)) {
+                await new Promise((resolve) => window.setTimeout(resolve, 1_000))
+                break
+              }
             }
+          } finally {
+            window.clearInterval(timer)
           }
 
-          window.clearInterval(timer)
           const classHits = Array.from(
             document.querySelectorAll(
               '.monaco-diff-editor .line-insert, .monaco-diff-editor .line-delete, .monaco-diff-editor .char-insert, .monaco-diff-editor .char-delete'

tests/e2e/large-diff-repro-fixtures.ts

@@ -69,10 +69,12 @@ export function createIsolatedStagedLocaleDiffRepo(): IsolatedStagedLocaleDiffRe
   runGit(repoPath, ['config', 'user.name', 'E2E Test'])
 
   mkdirSync(path.join(repoPath, 'src', 'locales'), { recursive: true })
+  const toAbsoluteFsPath = (relativePosixPath: string): string =>
+    path.join(repoPath, ...relativePosixPath.split(path.posix.sep))
   const relativePaths: string[] = []
   for (let fileIndex = 0; fileIndex < 5; fileIndex += 1) {
-    const relativePath = `src/locales/locale-${fileIndex}.json`
-    const absolutePath = path.join(repoPath, ...relativePath.split('/'))
+    const relativePath = path.posix.join('src', 'locales', `locale-${fileIndex}.json`)
+    const absolutePath = toAbsoluteFsPath(relativePath)
     const original = buildLocaleLikeJson(fileIndex, 3600)
     writeFileSync(absolutePath, original)
     relativePaths.push(relativePath)
@@ -81,7 +83,7 @@ export function createIsolatedStagedLocaleDiffRepo(): IsolatedStagedLocaleDiffRe
   runGit(repoPath, ['commit', '-m', 'Initial locale fixture'])
 
   for (let fileIndex = 0; fileIndex < relativePaths.length; fileIndex += 1) {
-    const absolutePath = path.join(repoPath, ...relativePaths[fileIndex].split('/'))
+    const absolutePath = toAbsoluteFsPath(relativePaths[fileIndex])
     const original = buildLocaleLikeJson(fileIndex, 3600)
     writeFileSync(absolutePath, modifyLocaleLikeJson(original, fileIndex))
   }