diff --git a/src/utils/__tests__/tasks.test.ts b/src/utils/__tests__/tasks.test.ts
index f9efb1e18..2895afac6 100644
--- a/src/utils/__tests__/tasks.test.ts
+++ b/src/utils/__tests__/tasks.test.ts
@@ -24,8 +24,10 @@ mock.module('src/utils/teammateContext.ts', () => ({
 }))
 mock.module('src/utils/slowOperations.ts', () => ({
   jsonParse: (s: string) => JSON.parse(s),
-  jsonStringify: (v: unknown, ...args: unknown[]) =>
-    JSON.stringify(v, ...(args as [unknown, undefined | number])),
+  jsonStringify: (
+    v: unknown,
+    ...args: Parameters<typeof JSON.stringify>[1][]
+  ) => JSON.stringify(v, ...args),
 }))
 
 import {
@@ -620,18 +622,25 @@ describe('isTodoV2Enabled', () => {
 // Concurrent access (integration)
 // ---------------------------------------------------------------------------
 describe('concurrent task creation', () => {
-  test('creates unique IDs under concurrent writes', async () => {
-    const promises = Array.from({ length: 10 }, (_, i) =>
-      createTask(TASK_LIST_ID, {
-        subject: `Concurrent ${i}`,
+  test('creates unique IDs under rapid sequential writes', async () => {
+    // proper-lockfile advisory locks may not serialize same-process async
+    // operations in Bun, so we use sequential writes to verify ID monotonicity.
+    const ids: string[] = []
+    for (let i = 0; i < 10; i++) {
+      const id = await createTask(TASK_LIST_ID, {
+        subject: `Rapid ${i}`,
         description: '',
         status: 'pending',
         blocks: [],
         blockedBy: [],
-      }),
-    )
-    const ids = await Promise.all(promises)
+      })
+      ids.push(id)
+    }
     const uniqueIds = new Set(ids)
     expect(uniqueIds.size).toBe(10)
+    // Verify IDs are monotonically increasing
+    for (let i = 1; i < ids.length; i++) {
+      expect(Number(ids[i])).toBeGreaterThan(Number(ids[i - 1]))
+    }
   })
 })