Import locomotive availability descriptors with overlay context

fixtures/runtime/packed-event-locomotive-availability-overlay-base-snapshot.json

@@ -0,0 +1,44 @@
+{
+  "format_version": 1,
+  "snapshot_id": "packed-event-locomotive-availability-overlay-base-snapshot",
+  "source": {
+    "description": "Base runtime snapshot supplying locomotive catalog context for descriptor-driven named locomotive availability import."
+  },
+  "state": {
+    "calendar": {
+      "year": 1835,
+      "month_slot": 1,
+      "phase_slot": 2,
+      "tick_slot": 4
+    },
+    "world_flags": {
+      "base.only": true
+    },
+    "metadata": {
+      "base.note": "preserve locomotive catalog context"
+    },
+    "locomotive_catalog": [
+      {
+        "locomotive_id": 10,
+        "name": "Locomotive 10"
+      },
+      {
+        "locomotive_id": 112,
+        "name": "Locomotive 112"
+      }
+    ],
+    "named_locomotive_availability": {
+      "Locomotive 10": 0,
+      "Locomotive 112": 1
+    },
+    "event_runtime_records": [],
+    "candidate_availability": {},
+    "special_conditions": {},
+    "service_state": {
+      "periodic_boundary_calls": 0,
+      "trigger_dispatch_counts": {},
+      "total_event_record_services": 0,
+      "dirty_rerun_count": 0
+    }
+  }
+}