Each (stage_id, replica_id) route allocated its 3 handshake/input/output
ports via a separate get_open_ports_list(count=3) call. That helper only
guarantees uniqueness *within* a single call, so across routes the OS could
hand back a just-closed ephemeral port. Two stages then drew the same port
and the second engine subprocess to bind() it died with
"zmq.error.ZMQError: Address already in use", surfacing as
"Orchestrator initialization failed" / "Stage N replica M exited before API
server became ready". This flaked multi-stage startup (e.g. Qwen3-Omni
thinker/talker/code2wav) — one CI shard passed while a parallel shard failed
on the same commit (build 2630, dev/vllm-align).
OmniMasterServer now tracks every port it hands out in self._allocated_ports
(seeded with the registration port and the coordinator ROUTER port) and a new
_alloc_unique_ports() redraws any collision with a bounded retry budget,
raising loudly on port exhaustion instead of spinning. Adds _port_from_zmq_address()
helper and two CPU-only regression tests.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
