feat(annotations): broadcast live-stroke geometry to plugin_events_group

AnnotationBasePtr is not Python-bound, so Python plugins cannot
subscribe to live_edit_event_group directly. Serialize the cumulative
in-progress stroke via Annotation::serialise() and broadcast it as a
JsonStore alongside (event_atom, annotation_data_atom, user_id,
stroke_completed) via plugin_events_group(), so Python plugins can
render partial strokes directly from event geometry instead of
polling/hot-scanning bookmarks. Shapes (Square/Circle/Arrow/Line/
Ellipse) are only broadcast on pen-up, since a shape isn't a
meaningful annotation until the drag completes.

Also fix subscribe_to_plugin_events: BroadcastActor forwards messages
via send_as(current_sender(), subscriber, msg), so a Python subscriber
sees the owning actor as the sender, not the broadcast group. The
2-arg add_message_callback() only registered the group's address, so
plugin_events_ messages were silently dropped. Pass the plugin's actor
as the owner_actor (3rd arg), mirroring the same fix already applied
to subscribe_to_event_group.

Signed-off-by: Sam.Richards@taurich.org <Sam.Richards@taurich.org>

Author: richardssam

python/src/xstudio/plugin/plugin_base.py

@@ -296,7 +296,7 @@ def subscribe_to_plugin_events(self, plugin, callback_method):
             raise Exception("Actor has no event group.")
 
         return self.connection.link.add_message_callback(
-            event_group, callback_method
+            event_group, callback_method, plugin.remote
             )
 
     def register_ui_panel_qml(self,

src/plugin/viewport_overlay/annotations/src/annotations_core_plugin.cpp

@@ -1291,13 +1291,34 @@ void AnnotationsCore::broadcast_live_stroke(
     if (user_edit_data->live_stroke)
         anno->canvas().append_item(*(user_edit_data->live_stroke));
 
-    mail(
-        utility::event_atom_v,
-        annotation_data_atom_v,
-        AnnotationBasePtr(anno),
-        user_id,
-        stroke_completed)
+    AnnotationBasePtr anno_ptr(anno);
+
+    mail(utility::event_atom_v, annotation_data_atom_v, anno_ptr, user_id, stroke_completed)
         .send(live_edit_event_group_);
+
+    // Python-accessible event: AnnotationBasePtr is not Python-bound, so broadcast
+    // the serialised geometry via plugin_events_ so Python plugins can render
+    // in-progress strokes directly, without polling/hot-scanning bookmarks.
+    // Shapes (as opposed to pen/brush strokes) are only broadcast on pen-up,
+    // since a shape isn't a meaningful annotation until the drag completes.
+    const bool is_shape = user_edit_data->item_type == Canvas::ItemType::Square ||
+                           user_edit_data->item_type == Canvas::ItemType::Circle ||
+                           user_edit_data->item_type == Canvas::ItemType::Arrow ||
+                           user_edit_data->item_type == Canvas::ItemType::Line ||
+                           user_edit_data->item_type == Canvas::ItemType::Ellipse;
+
+    if (!is_shape || stroke_completed) {
+        utility::Uuid plugin_uuid;
+        utility::JsonStore anno_json = anno_ptr->serialise(plugin_uuid);
+
+        mail(
+            utility::event_atom_v,
+            annotation_data_atom_v,
+            anno_json,
+            user_id,
+            stroke_completed)
+            .send(plugin_events_group());
+    }
 }
 
 void AnnotationsCore::broadcast_live_laser_stroke(