fix: serialize diagnostic log appends

src/background/diagnostic-log-store.ts

@@ -6,9 +6,12 @@ const MAX_RECENT_LOGS = 300;
 type DiagnosticStoreStorage = Pick<StorageManager, 'get' | 'set' | 'remove'>;
 
 export class DiagnosticLogStore {
+  private appendChain: Promise<void> = Promise.resolve();
+
   constructor(private readonly storageManager: DiagnosticStoreStorage = storage) {}
 
   async append(entry: DiagnosticLogEntry): Promise<void> {
+    const runAppend = async () => {
       const recent = await this.getRecent();
       const next = [...recent, entry];
 
@@ -17,6 +20,11 @@ export class DiagnosticLogStore {
       }
 
       await this.storageManager.set(DIAGNOSTIC_STORAGE_KEYS.RECENT_LOGS, next);
+    };
+
+    const appendPromise = this.appendChain.then(runAppend, runAppend);
+    this.appendChain = appendPromise.catch(() => undefined);
+    return appendPromise;
   }
 
   async getRecent(): Promise<DiagnosticLogEntry[]> {

tests/unit/diagnostic-log-store.test.ts

@@ -54,6 +54,33 @@ describe('DiagnosticLogStore', () => {
     expect(logs.at(-1)?.id).toBe('log-304');
   });
 
+  it('does not lose logs when append is called concurrently', async () => {
+    let currentLogs: DiagnosticLogEntry[] = [];
+
+    const concurrentStorage = {
+      get: vi.fn(async () => {
+        const snapshot = [...currentLogs];
+        await new Promise((resolve) => setTimeout(resolve, 0));
+        return snapshot;
+      }),
+      set: vi.fn(async (_key: string, value: DiagnosticLogEntry[]) => {
+        currentLogs = value;
+      }),
+      remove: vi.fn(async () => {}),
+    };
+
+    const store = new DiagnosticLogStore(concurrentStorage as any);
+
+    await Promise.all([
+      store.append({ id: 'log-a', level: 'INFO', message: 'A' }),
+      store.append({ id: 'log-b', level: 'INFO', message: 'B' }),
+    ]);
+
+    expect(currentLogs).toHaveLength(2);
+    expect(currentLogs.map((item) => item.id)).toEqual(['log-a', 'log-b']);
+  });
+
+
   it('clears the buffer without touching unrelated keys', async () => {
     const store = new DiagnosticLogStore(new StorageManager());