fix(plugin): drive headless tasks, invalidate layer cache, and handle cancel event

crates/ocs_plugin_api/src/ipc/client.rs

@@ -419,7 +419,12 @@ impl HostApi for PluginHostApi {
 
     fn add_layer(&mut self, config: crate::host::LayerConfig) -> Option<Handle> {
         match self.client.request(PluginRequest::AddLayer(config)) {
-            Ok(PluginResponse::OptHandle(h)) => h,
+            Ok(PluginResponse::OptHandle(h)) => {
+                if h.is_some() {
+                    self.document_cache = OnceCell::new();
+                }
+                h
+            }
             Ok(other) => {
                 eprintln!("[plugin] unexpected AddLayer response: {other:?}");
                 None
@@ -433,7 +438,12 @@ impl HostApi for PluginHostApi {
 
     fn modify_layer(&mut self, config: crate::host::LayerConfig) -> bool {
         match self.client.request(PluginRequest::ModifyLayer(config)) {
-            Ok(PluginResponse::Bool(b)) => b,
+            Ok(PluginResponse::Bool(b)) => {
+                if b {
+                    self.document_cache = OnceCell::new();
+                }
+                b
+            }
             Ok(other) => {
                 eprintln!("[plugin] unexpected ModifyLayer response: {other:?}");
                 false