diff --git a/tests/core/sched/test_omni_scheduler_forces_v1_model_runner.py b/tests/core/sched/test_omni_scheduler_forces_v1_model_runner.py
new file mode 100644
index 000000000..fb8546e2d
--- /dev/null
+++ b/tests/core/sched/test_omni_scheduler_forces_v1_model_runner.py
@@ -0,0 +1,59 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM-Omni project
+"""The omni scheduler must stay on the v1 model runner, like every omni worker.
+
+vLLM 0.28 resolved this config to v1; 0.29 ends its fallback chain with v2. When
+only the workers forced v1, the scheduler took its v2 fast path -- which omits
+resumed-request token ids -- while the v1 runner still read them, so resuming a
+request raised ``KeyError: <req_id>`` in ``_update_states`` and killed the engine
+core (Multi-Replica Startup Test).
+
+The default is upstream's to change, so this pins Omni's side of the contract
+rather than the default itself.
+"""
+
+from __future__ import annotations
+
+from types import SimpleNamespace
+
+import pytest
+
+from vllm_omni.core.sched.omni_scheduler_mixin import OmniSchedulerMixin
+
+pytestmark = [pytest.mark.core_model, pytest.mark.cpu]
+
+
+class _Scheduler(OmniSchedulerMixin):
+    """Minimal carrier for the shared init hook both omni schedulers call."""
+
+    def __init__(self, *, use_v2_model_runner: bool) -> None:
+        self.use_v2_model_runner = use_v2_model_runner
+        self.vllm_config = SimpleNamespace(
+            model_config=SimpleNamespace(
+                async_chunk=False,
+                stage_id=0,
+                pooling_output_decoder=None,
+            )
+        )
+        self._init_omni_io_scheduling_state()
+
+
+@pytest.mark.parametrize("initial", [True, False])
+def test_scheduler_ends_on_v1_model_runner(initial: bool) -> None:
+    """Whatever upstream resolves, the omni scheduler runs v1."""
+    assert _Scheduler(use_v2_model_runner=initial).use_v2_model_runner is False
+
+
+def test_v2_default_does_not_reach_the_resumed_request_fast_path() -> None:
+    """The v2 fast path is what dropped resumed-request token ids.
+
+    ``OmniGenerationScheduler`` branches on ``use_v2_model_runner`` when it
+    assembles SchedulerOutput; forcing it false keeps the v1 assembly that
+    carries ``all_token_ids`` for resumed requests, which the v1 runner reads.
+    """
+    scheduler = _Scheduler(use_v2_model_runner=True)
+
+    assert not scheduler.use_v2_model_runner, (
+        "scheduler would take the v2 fast path while omni workers run v1; "
+        "resumed requests then KeyError in _update_states"
+    )
diff --git a/vllm_omni/core/sched/omni_scheduler_mixin.py b/vllm_omni/core/sched/omni_scheduler_mixin.py
index aa71245a0..9123b794d 100644
--- a/vllm_omni/core/sched/omni_scheduler_mixin.py
+++ b/vllm_omni/core/sched/omni_scheduler_mixin.py
@@ -107,6 +107,17 @@ class OmniSchedulerMixin:
 
     def _init_omni_io_scheduling_state(self) -> None:
         """Initialize scheduler state shared by AR and generation stages."""
+        # Every omni worker forces the v1 model runner (the v2 runner carries no
+        # omni hooks), so the scheduler has to agree or the two disagree about
+        # what the SchedulerOutput carries. vLLM 0.29 defaults this to v2 where
+        # 0.28 did not, so the scheduler took its v2 fast path -- the one that
+        # deliberately omits resumed-request token ids -- while the v1 runner
+        # still read them, and resuming a request raised ``KeyError: <req_id>``
+        # in ``_update_states``.
+        if getattr(self, "use_v2_model_runner", False):
+            logger.warning("OMNI scheduler forces v1 model runner for omni hooks.")
+            self.use_v2_model_runner = False
+
         model_config = self.vllm_config.model_config
         self.chunk_transfer_adapter = (
             OmniChunkTransferAdapter(self.vllm_config) if getattr(model_config, "async_chunk", False) else None