Fix desktop settings first-launch race

packages/desktop/src/settings/desktop-settings.test.ts

@@ -43,6 +43,22 @@ describe("desktop-settings", () => {
     expect(persisted.settings).toEqual(DEFAULT_DESKTOP_SETTINGS);
   });
 
+  it("handles concurrent first-launch reads without racing the settings write", async () => {
+    const userDataPath = await createTempUserDataDir();
+    directories.add(userDataPath);
+    const store = createDesktopSettingsStore({ userDataPath });
+
+    const settings = await Promise.all(Array.from({ length: 20 }, () => store.get()));
+    const persisted = JSON.parse(await readFile(settingsFilePath(userDataPath), "utf8")) as {
+      settings: DesktopSettings;
+    };
+    const files = await readdir(userDataPath);
+
+    expect(settings).toEqual(Array.from({ length: 20 }, () => DEFAULT_DESKTOP_SETTINGS));
+    expect(persisted.settings).toEqual(DEFAULT_DESKTOP_SETTINGS);
+    expect(files).toEqual(["desktop-settings.json"]);
+  });
+
   it("coerces invalid persisted values back to safe defaults", async () => {
     const userDataPath = await createTempUserDataDir();
     directories.add(userDataPath);

packages/desktop/src/settings/desktop-settings.ts

@@ -1,3 +1,4 @@
+import { randomUUID } from "node:crypto";
 import { mkdir, readFile, rename, writeFile } from "node:fs/promises";
 import path from "node:path";
 
@@ -198,13 +199,19 @@ export function createDesktopSettingsStore({
 }): DesktopSettingsStore {
   const filePath = path.join(userDataPath, DESKTOP_SETTINGS_FILENAME);
   let cachedDocument: PersistedDesktopSettingsDocument | null = null;
+  let persistQueue: Promise<void> = Promise.resolve();
 
   async function persistDocument(document: PersistedDesktopSettingsDocument): Promise<void> {
-    await mkdir(userDataPath, { recursive: true });
+    const write = async () => {
-    const tempFilePath = `${filePath}.tmp`;
+      await mkdir(userDataPath, { recursive: true });
-    await writeFile(tempFilePath, `${JSON.stringify(document, null, 2)}\n`, "utf8");
+      const tempFilePath = `${filePath}.tmp.${process.pid}.${randomUUID()}`;
-    await rename(tempFilePath, filePath);
+      await writeFile(tempFilePath, `${JSON.stringify(document, null, 2)}\n`, "utf8");
-    cachedDocument = document;
+      await rename(tempFilePath, filePath);
+      cachedDocument = document;
+    };
+    const queued = persistQueue.then(write, write);
+    persistQueue = queued.catch(() => undefined);
+    await queued;
   }
 
   async function loadDocument(): Promise<PersistedDesktopSettingsDocument> {