fix(storage): retry transient notification outbox renames

Retry bounded Windows EPERM, EACCES, and EBUSY rename failures for asynchronous and startup outbox persistence while preserving atomic writes and immediate failure for permanent errors.

tests/notification-outbox.test.ts

@@ -296,6 +296,23 @@ describe("NotificationOutbox", () => {
     }
   });
 
+  it("retries a transient Windows rename failure before persisting", async () => {
+    const filePath = createOutboxFile();
+    const actualRename = fsp.rename;
+    const rename = vi.spyOn(fsp, "rename")
+      .mockRejectedValueOnce(Object.assign(new Error("locked"), { code: "EPERM" }))
+      .mockImplementation((oldPath, newPath) => actualRename(oldPath, newPath));
+    try {
+      const outbox = new NotificationOutbox({ filePath, now: () => 1000, send: async () => true });
+      await outbox.enqueue(event("rename-retry"));
+
+      expect(rename).toHaveBeenCalledTimes(2);
+      expect(persisted(filePath).events.map((queuedEvent) => queuedEvent.id)).toEqual(["rename-retry"]);
+    } finally {
+      rename.mockRestore();
+    }
+  });
+
   it("persists a cleaned empty legacy file atomically during load", () => {
     const filePath = createOutboxFile();
     const rename = vi.spyOn(fs, "renameSync");
@@ -328,6 +345,26 @@ describe("NotificationOutbox", () => {
     rename.mockRestore();
   });
 
+  it("retries a transient synchronous Windows rename failure during load", () => {
+    const filePath = createOutboxFile();
+    fs.writeFileSync(filePath, JSON.stringify({ version: 1, events: [], lastSuccessAt: 0, lastFailureAt: 0 }), "utf8");
+    const actualRenameSync = fs.renameSync;
+    const rename = vi.spyOn(fs, "renameSync")
+      .mockImplementationOnce(() => {
+        throw Object.assign(new Error("locked"), { code: "EBUSY" });
+      })
+      .mockImplementation((oldPath, newPath) => actualRenameSync(oldPath, newPath));
+    try {
+      const outbox = new NotificationOutbox({ filePath, send: async () => true, now: () => 1000 });
+
+      expect(outbox.getStatus().queued).toBe(0);
+      expect(rename).toHaveBeenCalledTimes(2);
+      expect(fs.existsSync(`${filePath}.tmp`)).toBe(false);
+    } finally {
+      rename.mockRestore();
+    }
+  });
+
   it("drops expired events before persisting or sending", async () => {
     const filePath = createOutboxFile();
     const send = vi.fn().mockResolvedValue(true);