Exercise document model lifecycle through plugin IPC

docs/plugin-host-model-completion-plan.md

@@ -104,3 +104,4 @@ Start with the **Phase 8 integration harness and coverage ledger**. Re-evaluate
 - The same Line test now also sends a duplicate-handle batch through Python and confirms the host rejects it without changing geometry or creating an undo entry.
 - The opt-in `staged_python_point_pick_and_cancel_over_real_ipc` test passes with the same runner. It requests point and entity picks through Python, drives the app's active-command point/object-pick callbacks, polls the returned tokens through a later Python run, and verifies Enter cancellation. The callbacks are invoked by the test harness, not by a physical GUI pointer event; live GUI verification remains open.
 - The opt-in `staged_python_tabs_isolate_tokens_and_notifications` test passes with two real OCS document tabs and the staged runner. A token created in tab 0 cannot be observed or consumed in tab 1 before or after completion. Host-to-plugin DrawingChanged notifications for both tab ids are delivered over IPC and drained only by their owning tab. A 257-event burst reports overflow, and `DocumentTabClosed` discards queued events for that tab.
+- Added `doc.create_entity(kind, **properties)` and `doc.delete_entity(entity_or_handle)` to the high-level Python document model. Unit tests cover forwarding and managed identity fields. The real staged-plugin Line lifecycle now uses these methods rather than low-level `ocs.add`/`remove_entity`.