fix: await optional file database saves

src/features/ConfigSync/PendingConfigSaves.unit.spec.ts

@@ -0,0 +1,84 @@
+import { afterEach, describe, expect, it, vi } from "vitest";
+import { PendingConfigSaves } from "./PendingConfigSaves";
+
+function deferred() {
+    let resolve!: () => void;
+    let reject!: (error: unknown) => void;
+    const promise = new Promise<void>((onResolve, onReject) => {
+        resolve = onResolve;
+        reject = onReject;
+    });
+    return { promise, resolve, reject };
+}
+
+afterEach(() => vi.useRealTimers());
+
+describe("pending customisation saves", () => {
+    it("retains the quiet period and completes every coalesced notification after the actual save", async () => {
+        vi.useFakeTimers();
+        const pending = new PendingConfigSaves();
+        const save = deferred();
+        const firstSave = vi.fn(async () => {});
+        const lastSave = vi.fn(() => save.promise);
+        const first = pending.enqueue("plugin", firstSave);
+        await vi.advanceTimersByTimeAsync(80);
+        const second = pending.enqueue("plugin", lastSave);
+        let completed = false;
+        const all = Promise.all([first, second]).then(() => {
+            completed = true;
+        });
+        await vi.advanceTimersByTimeAsync(99);
+        expect(lastSave).not.toHaveBeenCalled();
+        await vi.advanceTimersByTimeAsync(1);
+        expect(firstSave).not.toHaveBeenCalled();
+        expect(lastSave).toHaveBeenCalledOnce();
+        expect(completed).toBe(false);
+        save.resolve();
+        await all;
+        expect(completed).toBe(true);
+    });
+
+    it("flushes the captured group without waiting for or releasing later notifications", async () => {
+        vi.useFakeTimers();
+        const pending = new PendingConfigSaves();
+        const flush = deferred();
+        const lateFlush = deferred();
+        const firstSave = deferred();
+        const work = vi.fn(() => firstSave.promise);
+        const first = pending.enqueue("plugin", work, flush.promise);
+        const coalesced = pending.enqueue("plugin", work, lateFlush.promise);
+        flush.resolve();
+        await vi.advanceTimersByTimeAsync(0);
+        expect(work).toHaveBeenCalledOnce();
+        const nextWork = vi.fn(async () => {});
+        const later = pending.enqueue("plugin", nextWork);
+        lateFlush.resolve();
+        await vi.advanceTimersByTimeAsync(0);
+        expect(nextWork).not.toHaveBeenCalled();
+        firstSave.resolve();
+        await Promise.all([first, coalesced]);
+        expect(nextWork).not.toHaveBeenCalled();
+        await vi.advanceTimersByTimeAsync(100);
+        await later;
+        expect(nextWork).toHaveBeenCalledOnce();
+    });
+
+    it("rejects every coalesced notification with the original failure and permits a later retry", async () => {
+        vi.useFakeTimers();
+        const pending = new PendingConfigSaves();
+        const failure = new Error("database write failed");
+        const save = async () => {
+            throw failure;
+        };
+        const first = pending.enqueue("plugin", save);
+        const second = pending.enqueue("plugin", save);
+        const outcomes = Promise.allSettled([first, second]);
+        await vi.advanceTimersByTimeAsync(100);
+        expect(await outcomes).toEqual([
+            { status: "rejected", reason: failure },
+            { status: "rejected", reason: failure },
+        ]);
+        const retry = pending.enqueue("plugin", async () => {}, Promise.resolve());
+        await retry;
+    });
+});