Throw abort error if signal is pre-aborted

Respect pre-aborted AbortSignals immediately instead of attempting
the operation first. This ensures callers that abort before invoking
the retry function receive the expected rejection without unnecessary
execution.

src/shared/git-index-lock-retry.test.ts

@@ -45,6 +45,16 @@ describe('git index lock retry', () => {
     expect(run).toHaveBeenCalledTimes(2)
   })
 
+  it('rejects without running when the signal is already aborted', async () => {
+    vi.useFakeTimers()
+    const run = vi.fn<() => Promise<string>>().mockResolvedValue('ok')
+
+    await expect(runWithGitIndexLockRetry(run, AbortSignal.abort())).rejects.toMatchObject({
+      name: 'AbortError'
+    })
+    expect(run).not.toHaveBeenCalled()
+  })
+
   it('cancels a pending retry when the caller aborts', async () => {
     vi.useFakeTimers()
     const controller = new AbortController()

src/shared/git-index-lock-retry.ts

@@ -51,6 +51,9 @@ export async function runWithGitIndexLockRetry<T>(
   signal?: AbortSignal
 ): Promise<T> {
   for (let attempt = 0; ; attempt += 1) {
+    if (signal?.aborted) {
+      throw createAbortError()
+    }
     try {
       return await run()
     } catch (error) {