feat: unify worker lifecycle restore semantics

crates/protocol/src/subscription.rs

@@ -557,7 +557,6 @@ pub enum SubscriptionWorkerState {
     Running,
     Paused,
     Stopped,
-    Cancelled,
 }
 
 #[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
@@ -1110,6 +1109,25 @@ mod tests {
         );
     }
 
+    #[test]
+    fn worker_subscription_state_has_exactly_four_lifecycle_values() {
+        for (state, wire) in [
+            (SubscriptionWorkerState::Idle, "idle"),
+            (SubscriptionWorkerState::Running, "running"),
+            (SubscriptionWorkerState::Paused, "paused"),
+            (SubscriptionWorkerState::Stopped, "stopped"),
+        ] {
+            assert_eq!(
+                serde_json::to_value(state).unwrap(),
+                serde_json::json!(wire)
+            );
+        }
+        assert!(
+            serde_json::from_value::<SubscriptionWorkerState>(serde_json::json!("cancelled"))
+                .is_err()
+        );
+    }
+
     #[test]
     fn client_selector_has_no_workspace_scope_field() {
         let json = serde_json::to_value(EventSubscriptionSelector::WorkspaceWorkers).unwrap();