fix: honor live scheduling revisions at dispatch

tests/scheduling/test_preparation.py

@@ -56,9 +56,15 @@ def _scheduler(
 ) -> tuple[Scheduler, FileScheduleStore, FileRunStore]:
     sched_store = FileScheduleStore(tmp_path / "sched")
     run_store = FileRunStore(tmp_path / "runs")
+
+    def revisioned_fixture_environment(sched: Any) -> Any:
+        environment = fixture_environment(sched)
+        deployment = environment.deployment.model_copy(update={"revision": 3})
+        return environment.model_copy(update={"deployment": deployment})
+
     preparer = SchedulePreparer(
         DictDeployments({"dep-1": {"rev": 3, "required": []}}),
-        fixture_environment,
+        revisioned_fixture_environment,
     )
     sched = Scheduler(
         schedule_store=sched_store,
@@ -159,6 +165,23 @@ def test_unknown_deployment_rejects_without_a_run(tmp_path: Path) -> None:
     sched.ownership.release()
 
 
+def test_deployment_revision_mismatch_rejects_pinned_environment() -> None:
+    """Preparation fails when directory metadata no longer matches the pin."""
+    preparer = SchedulePreparer(
+        DictDeployments({"dep-1": {"rev": 2, "required": []}}),
+        fixture_environment,
+    )
+
+    result = preparer.prepare(
+        sched=_sched_model("s"),
+        intended=ts(2026, 9, 8, 12, 0),
+        now=ts(2026, 9, 8, 12, 0),
+    )
+
+    assert isinstance(result, PreparationRejected)
+    assert result.reason == "deployment-changed"
+
+
 def test_missing_required_input_rejects_without_a_run(tmp_path: Path) -> None:
     sched_store = FileScheduleStore(tmp_path / "sched")
     run_store = FileRunStore(tmp_path / "runs")