Date each customer's cumulative spend first crossed 1000

Table orders:

For each customer, find the date on which their running total of amount (orders in created_at order, ties by id) first reached 1000 or more. Customers who never reach 1000 are not listed.

Output columns: customer_id, crossed_on (date).

CREATE TABLE orders (
  id int PRIMARY KEY,
  customer_id int NOT NULL,
  amount int NOT NULL CHECK (amount > 0),
  created_at timestamp NOT NULL
);