Pipeline boundaries — where one agent's job ends — step 6 of 7

The orchestrator is code, not an agent — a loop that walks the stages in order and stops at the first boundary whose artifact failed its check. Write first_blocked(stages):

• Walk stages in order.
• Return the name of the first stage whose artifact_ok is False — that's where the pipeline halts and the producer retries.
• If every artifact passed, return "ship".

Two pipelines run. Expected output:

review
ship