diff --git a/rlix/pipeline/miles_model_update_service.py b/rlix/pipeline/miles_model_update_service.py
index 6371f38..e3e8093 100644
--- a/rlix/pipeline/miles_model_update_service.py
+++ b/rlix/pipeline/miles_model_update_service.py
@@ -190,13 +190,17 @@ async def sync_selected_workers(
             )
         cpu_serialize_set = target - broadcast_set
 
-        # R06-F1 fix: track every Ray ObjectRef issued by this atomic
-        # unit so an asyncio.wait_for timeout (or any other cancellation)
-        # can fan out ray.cancel(force=True) on them. Without this, the
-        # local coroutine cancels but the Ray actor methods on
-        # cache_owner / rollout_manager keep running and continue to
-        # hold cache_owner._cache_lock — the next sync_selected_workers
-        # call would queue behind the still-executing prior method.
+        # R06-F1: track every Ray ObjectRef issued by this atomic unit so
+        # an asyncio.wait_for timeout (or any other cancellation) can fan
+        # out ray.cancel on them. Scope of what cancel can actually do
+        # (Ray actor-task semantics): QUEUED tasks are cancelled and never
+        # start; a task already EXECUTING on the sync cache_owner /
+        # rollout_manager actors cannot be interrupted (Ray only sets a
+        # cooperative is_canceled() flag that miles does not poll), so a
+        # running run_sync_session keeps holding cache_owner._cache_lock
+        # until it finishes and the next sync queues behind it. Preventing
+        # the queued follow-up RPCs (finalize / set_weight_version /
+        # try_put) from firing after a timeout is the effective win here.
         inflight_refs: list = []
 
         async def _run() -> int:
@@ -235,7 +239,14 @@ def _cancel_inflight(self, inflight_refs: list, *, reason: str) -> None:
         )
         for ref in inflight_refs:
             try:
-                ray.cancel(ref, force=True)
+                # force=False is the ONLY mode Ray allows for actor tasks —
+                # force=True raises ValueError before cancelling anything
+                # (docs: "Only force=False is allowed for an Actor Task"),
+                # which made this whole fan-out a silent no-op. force=False
+                # cancels queued tasks; executing tasks on sync actors run
+                # to completion (see the R06-F1 note in
+                # sync_selected_workers).
+                ray.cancel(ref, force=False)
             except Exception as exc:  # noqa: BLE001
                 logger.warning(
                     "ray.cancel failed pipeline_id=%s reason=%s exc=%r",
diff --git a/tests/test_miles_service_cancel_inflight.py b/tests/test_miles_service_cancel_inflight.py
new file mode 100644
index 0000000..176543f
--- /dev/null
+++ b/tests/test_miles_service_cancel_inflight.py
@@ -0,0 +1,90 @@
+"""Regression test for _cancel_inflight's Ray actor-task cancel semantics.
+
+Every ref in ``inflight_refs`` is an actor-method ObjectRef, and Ray only
+allows ``force=False`` for actor tasks — ``force=True`` raises ValueError
+before cancelling anything, which made the R06-F1 fan-out a silent no-op
+(each ValueError was swallowed by the per-ref try/except). Pin that every
+cancel goes out with ``force=False`` and actually reaches ray.cancel.
+"""
+
+from __future__ import annotations
+
+import importlib
+import sys
+import types
+from pathlib import Path
+
+import pytest
+
+REPO_ROOT = Path(__file__).resolve().parents[1]
+RLIX_ROOT = REPO_ROOT / "rlix"
+
+
+def _install_import_stubs(monkeypatch: pytest.MonkeyPatch) -> tuple[list, types.ModuleType]:
+    for module_name in list(sys.modules):
+        if module_name == "ray" or module_name.startswith("rlix"):
+            monkeypatch.delitem(sys.modules, module_name, raising=False)
+
+    ray_stub = types.ModuleType("ray")
+    cancel_calls: list = []
+
+    def _remote(*args, **kwargs):
+        # Support both bare ``@ray.remote`` (class passed directly) and
+        # ``@ray.remote(...)`` / ``ray.remote(cls)`` forms.
+        if len(args) == 1 and callable(args[0]) and not kwargs:
+            return args[0]
+
+        def _decorate(obj):
+            return obj
+
+        return _decorate
+
+    def _cancel(ref, *, force=False, recursive=True):
+        # Mirror Ray's actor-task contract: force=True raises ValueError
+        # before any cancellation happens.
+        if force:
+            raise ValueError("force=True is not allowed for an Actor Task")
+        cancel_calls.append((ref, force))
+
+    ray_stub.remote = _remote
+    ray_stub.cancel = _cancel
+    ray_stub.get = lambda ref, timeout=None: ref
+    ray_stub.get_actor = lambda *args, **kwargs: None
+    monkeypatch.setitem(sys.modules, "ray", ray_stub)
+
+    package_roots = {
+        "rlix": RLIX_ROOT,
+        "rlix.pipeline": RLIX_ROOT / "pipeline",
+        "rlix.protocol": RLIX_ROOT / "protocol",
+        "rlix.utils": RLIX_ROOT / "utils",
+    }
+    for module_name, module_path in package_roots.items():
+        package_module = types.ModuleType(module_name)
+        package_module.__path__ = [str(module_path)]  # type: ignore[attr-defined]
+        monkeypatch.setitem(sys.modules, module_name, package_module)
+
+    return cancel_calls, ray_stub
+
+
+def test_cancel_inflight_uses_force_false_and_cancels_every_ref(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    cancel_calls, _ = _install_import_stubs(monkeypatch)
+    module = importlib.import_module("rlix.pipeline.miles_model_update_service")
+
+    service = module.MilesModelUpdateService(
+        pipeline_id="miles_test",
+        cache_owner_actor=object(),
+        rollout_manager=object(),
+    )
+
+    refs = ["ref_a", "ref_b", "ref_c"]
+    inflight = list(refs)
+    service._cancel_inflight(inflight, reason="unit-test")
+
+    # Every ref reached ray.cancel with force=False (force=True would have
+    # raised inside the stub and never recorded the call — the pre-fix
+    # silent-no-op behavior).
+    assert cancel_calls == [(ref, False) for ref in refs]
+    # The list is drained so a second timeout cannot double-cancel.
+    assert inflight == []