fix(cron): retry rename on EBUSY and fall back to copyFile on Windows

Landed from contributor PR #16932 with additional changelog alignment and verification.

src/cron/store.test.ts

@@ -92,3 +92,56 @@ describe("cron store", () => {
     await store.cleanup();
   });
 });
+
+describe("saveCronStore", () => {
+  const dummyStore: CronStoreFile = { version: 1, jobs: [] };
+
+  it("persists and round-trips a store file", async () => {
+    const { storePath, cleanup } = await makeStorePath();
+    await saveCronStore(storePath, dummyStore);
+    const loaded = await loadCronStore(storePath);
+    expect(loaded).toEqual(dummyStore);
+    await cleanup();
+  });
+
+  it("retries rename on EBUSY then succeeds", async () => {
+    const { storePath, cleanup } = await makeStorePath();
+
+    const origRename = fs.rename.bind(fs);
+    let ebusyCount = 0;
+    const spy = vi.spyOn(fs, "rename").mockImplementation(async (src, dest) => {
+      if (ebusyCount < 2) {
+        ebusyCount++;
+        const err = new Error("EBUSY") as NodeJS.ErrnoException;
+        err.code = "EBUSY";
+        throw err;
+      }
+      return origRename(src, dest);
+    });
+
+    await saveCronStore(storePath, dummyStore);
+    expect(ebusyCount).toBe(2);
+    const loaded = await loadCronStore(storePath);
+    expect(loaded).toEqual(dummyStore);
+
+    spy.mockRestore();
+    await cleanup();
+  });
+
+  it("falls back to copyFile on EPERM (Windows)", async () => {
+    const { storePath, cleanup } = await makeStorePath();
+
+    const spy = vi.spyOn(fs, "rename").mockImplementation(async () => {
+      const err = new Error("EPERM") as NodeJS.ErrnoException;
+      err.code = "EPERM";
+      throw err;
+    });
+
+    await saveCronStore(storePath, dummyStore);
+    const loaded = await loadCronStore(storePath);
+    expect(loaded).toEqual(dummyStore);
+
+    spy.mockRestore();
+    await cleanup();
+  });
+});

src/cron/store.ts

@@ -71,5 +71,30 @@ export async function saveCronStore(storePath: string, store: CronStoreFile) {
       // best-effort
     }
   }
-  await fs.promises.rename(tmp, storePath);
+  await renameWithRetry(tmp, storePath);
+}
+
+const RENAME_MAX_RETRIES = 3;
+const RENAME_BASE_DELAY_MS = 50;
+
+async function renameWithRetry(src: string, dest: string): Promise<void> {
+  for (let attempt = 0; attempt <= RENAME_MAX_RETRIES; attempt++) {
+    try {
+      await fs.promises.rename(src, dest);
+      return;
+    } catch (err) {
+      const code = (err as { code?: string }).code;
+      if (code === "EBUSY" && attempt < RENAME_MAX_RETRIES) {
+        await new Promise((resolve) => setTimeout(resolve, RENAME_BASE_DELAY_MS * 2 ** attempt));
+        continue;
+      }
+      // Windows doesn't reliably support atomic replace via rename when dest exists.
+      if (code === "EPERM" || code === "EEXIST") {
+        await fs.promises.copyFile(src, dest);
+        await fs.promises.unlink(src).catch(() => {});
+        return;
+      }
+      throw err;
+    }
+  }
 }