diff --git a/src/features/team-mode/team-tasklist/store.test.ts b/src/features/team-mode/team-tasklist/store.test.ts
new file mode 100644
index 000000000..f23fa74e6
--- /dev/null
+++ b/src/features/team-mode/team-tasklist/store.test.ts
@@ -0,0 +1,32 @@
+/// <reference types="bun-types" />
+
+import { expect, test } from "bun:test"
+import { readFile } from "node:fs/promises"
+import path from "node:path"
+
+import { getTasksDir, resolveBaseDir } from "../team-registry"
+import { createTask } from "./store"
+import { createTaskInput, createTasklistFixture } from "./test-support"
+
+test("createTask assigns distinct ids during concurrent creation", async () => {
+  // given
+  const fixture = await createTasklistFixture()
+
+  try {
+    // when
+    const [firstTask, secondTask] = await Promise.all([
+      createTask(fixture.teamRunId, createTaskInput({ subject: "first task" }), fixture.config),
+      createTask(fixture.teamRunId, createTaskInput({ subject: "second task" }), fixture.config),
+    ])
+
+    const tasksDirectory = getTasksDir(resolveBaseDir(fixture.config), fixture.teamRunId)
+    const watermarkContent = await readFile(path.join(tasksDirectory, ".highwatermark"), "utf8")
+    const sortedIds = [firstTask.id, secondTask.id].sort((leftId, rightId) => Number(leftId) - Number(rightId))
+
+    // then
+    expect(sortedIds).toEqual(["1", "2"])
+    expect(watermarkContent.trim()).toBe("2")
+  } finally {
+    await fixture.cleanup()
+  }
+})
diff --git a/src/features/team-mode/team-tasklist/store.ts b/src/features/team-mode/team-tasklist/store.ts
new file mode 100644
index 000000000..9a703839b
--- /dev/null
+++ b/src/features/team-mode/team-tasklist/store.ts
@@ -0,0 +1,53 @@
+import { mkdir, readFile } from "node:fs/promises"
+import path from "node:path"
+
+import type { TeamModeConfig } from "../../../config/schema/team-mode"
+import { getTasksDir, resolveBaseDir } from "../team-registry"
+import { atomicWrite, withLock } from "../team-state-store/locks"
+import { TaskSchema } from "../types"
+import type { Task } from "../types"
+
+const HIGH_WATERMARK_FILE = ".highwatermark"
+
+async function readHighWatermark(watermarkPath: string): Promise<number> {
+  try {
+    const watermarkContent = (await readFile(watermarkPath, "utf8")).trim()
+    const parsedWatermark = Number.parseInt(watermarkContent, 10)
+    return Number.isInteger(parsedWatermark) && parsedWatermark >= 0 ? parsedWatermark : 0
+  } catch {
+    await atomicWrite(watermarkPath, "0")
+    return 0
+  }
+}
+
+export async function createTask(
+  teamRunId: string,
+  taskInput: Omit<Task, "id" | "createdAt" | "updatedAt" | "version">,
+  config: TeamModeConfig,
+): Promise<Task> {
+  const tasksDirectory = getTasksDir(resolveBaseDir(config), teamRunId)
+  await mkdir(tasksDirectory, { recursive: true, mode: 0o700 })
+  await mkdir(path.join(tasksDirectory, "claims"), { recursive: true, mode: 0o700 })
+
+  return withLock(path.join(tasksDirectory, ".lock"), async () => {
+    const watermarkPath = path.join(tasksDirectory, HIGH_WATERMARK_FILE)
+    const nextTaskId = (await readHighWatermark(watermarkPath)) + 1
+    await atomicWrite(watermarkPath, String(nextTaskId))
+
+    const now = Date.now()
+    const task = TaskSchema.parse({
+      ...taskInput,
+      version: 1,
+      id: String(nextTaskId),
+      createdAt: now,
+      updatedAt: now,
+    })
+
+    await atomicWrite(
+      path.join(tasksDirectory, `${task.id}.json`),
+      `${JSON.stringify(task, null, 2)}\n`,
+    )
+
+    return task
+  }, { ownerTag: `create-task:${teamRunId}` })
+}