fix(sglang): Port collision when colocating 2 workers on same node with DP

[trevor-m]

When colocating multiple workers on a single node, srt-slurm assigns each worker's kv event publisher a port sequentially:

Worker 0 gets port 5200

^[[2m2026-10-06T19:35:29.513690Z^[[0m ^[[32m INFO^[[0m ^[[2margs.parse_args^[[0m^[[2m:^[[0m Derived use_kv_events=True from kv_events_config={"publisher": "zmq", "topic": "kv-events", "endpoint": "tcp://*:5200"}

Worker 1 gets port 5201

^[[2m2026-10-06T19:35:28.575815Z^[[0m ^[[32m INFO^[[0m ^[[2margs.parse_args^[[0m^[[2m:^[[0m Derived use_kv_events=True from kv_events_config={"publisher": "zmq", "topic": "kv-events", "endpoint": "tcp://*:5201"}

However, if we are using DP then sglang will apply dp worker rank as an offset to the base kv event publisher port to determine that DP worker's port. This will lead to a collision since worker 0 rank 1 will get port 5200+1 which collides with worker 1 rank 0 port.

[2026-10-06 12:38:42 DP0 TP0 EP0] Starting ZMQ publisher thread
[2026-10-06 12:38:42 DP1 TP1 EP1] Scheduler hit an exception: Traceback (most recent call last):
  File "/sgl-workspace/sglang/python/sglang/srt/managers/scheduler.py", line 6082, in run_scheduler_process
    scheduler = Scheduler(server_args, port_args)
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/sgl-workspace/sglang/python/sglang/srt/managers/scheduler.py", line 705, in __init__
    self.init_kv_events_publisher()
  File "/sgl-workspace/sglang/python/sglang/srt/managers/scheduler.py", line 2393, in init_kv_events_publisher
    self.kv_events_publisher = SchedulerKvEventsPublisher( 
                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "<string>", line 11, in __init__
  File "/sgl-workspace/sglang/python/sglang/srt/managers/scheduler_components/kv_events_publisher.py", line 57, in __post_init__
    self.init_kv_events(self.kv_events_config)
  File "/sgl-workspace/sglang/python/sglang/srt/managers/scheduler_components/kv_events_publisher.py", line 64, in init_kv_events
    self.kv_event_publisher = EventPublisherFactory.create(
                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/sgl-workspace/sglang/python/sglang/srt/disaggregation/kv_events.py", line 646, in create
    return constructor(attn_dp_rank=attn_dp_rank, **config_dict)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/sgl-workspace/sglang/python/sglang/srt/disaggregation/kv_events.py", line 394, in __init__
    self._socket_setup()
  File "/sgl-workspace/sglang/python/sglang/srt/disaggregation/kv_events.py", line 472, in _socket_setup
    self._pub.bind(self._endpoint)
  File "/opt/sglang/lib/python3.12/site-packages/zmq/sugar/socket.py", line 322, in bind
    super().bind(addr)
  File "zmq/backend/cython/_zmq.py", line 1009, in zmq.backend.cython._zmq.Socket.bind
    _check_rc(rc)
    ^^^^^^^^^^^
  File "zmq/backend/cython/_zmq.py", line 190, in zmq.backend.cython._zmq._check_rc
    raise ZMQError(errno)
    ^^^^^^^^^^^
zmq.error.ZMQError: Address already in use (addr='tcp://*:5201')

To fix this, we spread out the base kv event publisher port for each worker based on the dp size, so worker 0 gets 5200 and worker 1 gets 5202 for example.

[github-actions]

src/srtctl diff: +50 -28

[codecov-commenter]

Codecov Report

❌ Patch coverage is 94.73684% with 1 line in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (main@4406bb7). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
src/srtctl/backends/sglang.py	94.44%	1 Missing ⚠️

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