test: add missing fallback test scenarios for useHighlightedFile

Add single-chunk equivalence test (≤200 lines produces complete token
map with no missing line entries) and AbortController abort spy test
(unmount during chunked fallback triggers abort signal) to cover the
remaining spec scenarios not included by the implementation branch.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/web/src/components/review/use-syntax-highlight.fallback.test.ts

@@ -67,4 +67,65 @@ describe('useHighlightedFile — fallback path (Worker unavailable)', () => {
     expect(result.current?.get(1)).toEqual([MOCK_TOKEN_A])
     expect(result.current?.get(2)).toEqual([MOCK_TOKEN_B])
   })
+
+  it('returns a complete token map with no lines missing for ≤200-line input (single-chunk equivalence)', async () => {
+    const { useHighlightedFile } = await import('./use-syntax-highlight')
+
+    // 5 lines — well within the 200-line chunk size, so a single codeToTokens call handles all
+    const MOCK_TOKENS = [
+      [{ content: 'line1', color: '#fff', offset: 0 }],
+      [{ content: 'line2', color: '#fff', offset: 0 }],
+      [{ content: 'line3', color: '#fff', offset: 0 }],
+      [{ content: 'line4', color: '#fff', offset: 0 }],
+      [{ content: 'line5', color: '#fff', offset: 0 }],
+    ]
+    mockCodeToTokens.mockReturnValueOnce({ tokens: MOCK_TOKENS })
+
+    const lines = [1, 2, 3, 4, 5].map((n) => ({
+      content: `line${n}`,
+      newLineNumber: n,
+      type: 'context' as const,
+    }))
+
+    const { result } = renderHook(() => useHighlightedFile('src/bar.ts', lines))
+
+    await waitFor(
+      () => {
+        expect(result.current).not.toBeNull()
+      },
+      { timeout: 5000 },
+    )
+
+    // All 5 line numbers must be present — no lines missing
+    expect(result.current!.size).toBe(5)
+    for (let n = 1; n <= 5; n++) {
+      expect(result.current!.get(n)).toEqual(MOCK_TOKENS[n - 1])
+    }
+  })
+
+  it('calls AbortController.abort() when component unmounts during chunked fallback', async () => {
+    const { useHighlightedFile } = await import('./use-syntax-highlight')
+
+    const abortSpy = vi.spyOn(AbortController.prototype, 'abort')
+
+    // Delay the mock so the hook is still in-flight when we unmount
+    mockCodeToTokens.mockImplementationOnce(
+      () =>
+        new Promise((resolve) =>
+          setTimeout(() => resolve({ tokens: [[MOCK_TOKEN_A]] }), 500),
+        ),
+    )
+
+    const lines = [{ content: 'const x = 1', newLineNumber: 1, type: 'added' as const }]
+
+    const { unmount } = renderHook(() => useHighlightedFile('unmount.ts', lines))
+
+    // Unmount while the async chunked highlight is still pending
+    unmount()
+
+    // The cleanup function calls abortController.abort()
+    expect(abortSpy).toHaveBeenCalled()
+
+    abortSpy.mockRestore()
+  })
 })