diff --git a/src/app/api/v1/collection-map/items/[id]/assign/route.test.ts b/src/app/api/v1/collection-map/items/[id]/assign/route.test.ts
index f3ada73..6a043cc 100644
--- a/src/app/api/v1/collection-map/items/[id]/assign/route.test.ts
+++ b/src/app/api/v1/collection-map/items/[id]/assign/route.test.ts
@@ -96,4 +96,23 @@ describe("PATCH /api/v1/collection-map/items/[id]/assign", () => {
     // The unmark path must not silently overwrite the existing note.
     expect(payload.notes).toBeUndefined();
   });
+
+  it("clears assigned_at when returning an item to the pool (no driverId)", async () => {
+    getOneMock.mockResolvedValueOnce({
+      id: "item-1",
+      assigned_at: "2026-07-09T00:00:00.000Z",
+    });
+    updateMock.mockResolvedValueOnce({ id: "item-1" });
+
+    const res = await PATCH(
+      makeReq({ date: "" }),
+      { params: Promise.resolve({ id: "item-1" }) },
+    );
+
+    expect(res.status).toBe(200);
+    const payload = updateMock.mock.calls[0][1] as Record<string, unknown>;
+    expect(payload.assigned_at).toBe("");
+    expect(payload.item_status).toBe("collection_pool");
+    expect(payload.drv_status).toBe("unassigned");
+  });
 });
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