Host side of HostApi::set_reference_only: plugin-owned display geometry that
renders and snaps normally but must not be edited or picked by the person at
the screen, while the owning plugin keeps full write access through the host.
- Storage: a human-readable marker value in an XDATA record under the
host-owned OCS APPID (registered on first use; foreign values survive
verbatim; stale verbatim DWG EED is dropped on rewrite), so the flag
round-trips DWG and DXF with the entity and cannot collide with plugin
APPID namespaces.
- Grips: refresh_selected_grips yields none for a reference-only entity and
an active grip edit on a newly designated target is cancelled like a
locked-layer one.
- Picking: a reference-only wire flag extends the snap_only skips in every
hit test, so a click passes through to the editable entity underneath, and
box, window, lasso, fence and select-all gathers skip the designation;
fills, solids and instanced meshes are excluded through the shared
candidate handle set.
- Write policy: built-in user paths treat a reference-only entity like a
locked-layer one (Scene::update_entity / update_entities refuse,
erase_entities skips), while the plugin-owned variants
(update_entity_plugin / erase_entities_plugin, mirroring the
remove_entities editor split) and the whole HostSession surface write
through. The MCP entities read exposes a top-level reference_only boolean
and set_properties refuses with the reference_only failure code.
- Undo: the entity-write contract - a change joins a plugin-opened push_undo
scope, a scope-less change is one undo step of its own, refusals and
idempotent re-marks record nothing.
- Known limit: entities nested inside block instances (the block cache
rebuilds instance wires without the flag).
Evidence: marking_flags_and_unmarking_clears,
foreign_values_under_the_host_app_id_survive, other_apps_are_untouched,
reference_only_refusals_record_no_undo_step,
reference_only_designation_composes_undo_like_entity_writes,
reference_only_survives_dxf_and_dwg_round_trips,
user_paths_refuse_and_plugin_paths_write_reference_only_entities,
select_all_visible_skips_reference_only_entities,
clicks_pass_through_reference_only_wires,
box_selections_skip_reference_only_wires,
entities_records_expose_the_reference_only_designation.
