feat(plugin): persist XDATA to DWG and let plugins modify/delete entities (#249, #250)

#249 — plugin XDATA written via write_record survived only in memory: the
acadrust DWG writer dropped ExtendedData::records on save. Bump acadrust to
e88a9a6 (records now encode to EED and decode back on read) and fix the host
side that fed it:
  - ensure_app_id allocates a real APPID handle; a null handle serializes as
    0 and the EED reference can't resolve, so the XDATA vanished on reopen.
  - write_record / remove_record drop stale raw_dwg_eed for the target app so
    an edit made after a save/reopen wins over the pre-edit bytes.

#250 — out-of-process plugins got a throwaway document_mut() snapshot, so
edits to existing entities were silently discarded and deletion wasn't
expressible at all. Add the missing mutation surface:
  - UpdateEntity / RemoveEntity IPC requests + HostApi::update_entity /
    remove_entity (default in-process impls, RPC overrides on the client that
    invalidate the stale document cache).
  - Scene::update_entity replaces the entity in place, preserving its handle
    and owning block, and reseeds only its derived caches; remove reuses the
    cache-coherent erase_entities (which also honours layer locks).
  - document_mut() is documented as a local-only snapshot out-of-process.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

crates/ocs_plugin_api/src/ipc/client.rs

@@ -151,6 +151,46 @@ impl HostApi for PluginHostApi {
         }
     }
 
+    fn update_entity(&mut self, entity: EntityType) -> bool {
+        match self.client.request(PluginRequest::UpdateEntity(entity)) {
+            Ok(PluginResponse::Bool(b)) => {
+                if b {
+                    // The cached snapshot is now stale; drop it so a later
+                    // document() re-fetches the host's post-edit truth.
+                    self.document_cache = OnceCell::new();
+                }
+                b
+            }
+            Ok(other) => {
+                eprintln!("[plugin] unexpected UpdateEntity response: {other:?}");
+                false
+            }
+            Err(e) => {
+                eprintln!("[plugin] UpdateEntity failed: {e}");
+                false
+            }
+        }
+    }
+
+    fn remove_entity(&mut self, handle: Handle) -> bool {
+        match self.client.request(PluginRequest::RemoveEntity { handle }) {
+            Ok(PluginResponse::Bool(b)) => {
+                if b {
+                    self.document_cache = OnceCell::new();
+                }
+                b
+            }
+            Ok(other) => {
+                eprintln!("[plugin] unexpected RemoveEntity response: {other:?}");
+                false
+            }
+            Err(e) => {
+                eprintln!("[plugin] RemoveEntity failed: {e}");
+                false
+            }
+        }
+    }
+
     fn bump_geometry(&mut self) {
         let _ = self.client.request(PluginRequest::BumpGeometry);
     }
@@ -438,4 +478,36 @@ mod tests {
         peer_handle.join().unwrap();
         assert_eq!(handle, Handle::new(42));
     }
+
+    #[test]
+    fn update_entity_awaits_bool_response() {
+        let (mut api, mut peer) = make_client();
+        let peer_handle = thread::spawn(move || {
+            let msg = recv::<PluginToHost>(&mut peer).unwrap();
+            match msg {
+                PluginToHost::Request(PluginRequest::UpdateEntity(_)) => {}
+                other => panic!("unexpected: {other:?}"),
+            }
+            send(&mut peer, &HostToPlugin::Response(PluginResponse::Bool(true))).unwrap();
+        });
+        assert!(api.update_entity(EntityType::Point(Point::new())));
+        peer_handle.join().unwrap();
+    }
+
+    #[test]
+    fn remove_entity_awaits_bool_response() {
+        let (mut api, mut peer) = make_client();
+        let peer_handle = thread::spawn(move || {
+            let msg = recv::<PluginToHost>(&mut peer).unwrap();
+            match msg {
+                PluginToHost::Request(PluginRequest::RemoveEntity { handle }) => {
+                    assert_eq!(handle, Handle::new(7));
+                }
+                other => panic!("unexpected: {other:?}"),
+            }
+            send(&mut peer, &HostToPlugin::Response(PluginResponse::Bool(true))).unwrap();
+        });
+        assert!(api.remove_entity(Handle::new(7)));
+        peer_handle.join().unwrap();
+    }
 }

crates/ocs_plugin_api/src/ipc/protocol.rs

@@ -75,6 +75,12 @@ pub enum PluginRequest {
     PushOutput(String),
     PushError(String),
     AddEntity(EntityType),
+    /// Replace the existing entity carrying this entity's handle in place.
+    UpdateEntity(EntityType),
+    /// Delete the entity with `handle`.
+    RemoveEntity {
+        handle: Handle,
+    },
     BumpGeometry,
     ReadRecord {
         handle: Handle,

crates/ocs_plugin_api/src/ipc/server.rs

@@ -28,6 +28,8 @@ pub fn handle_plugin_request(
             PluginResponse::Ok
         }
         AddEntity(entity) => PluginResponse::Handle(host.add_entity(entity)),
+        UpdateEntity(entity) => PluginResponse::Bool(host.update_entity(entity)),
+        RemoveEntity { handle } => PluginResponse::Bool(host.remove_entity(handle)),
         BumpGeometry => {
             host.bump_geometry();
             PluginResponse::Ok