Refresh the Insert and Polyline wording in the design notes and plan

Co-Authored-By: Claude Sonnet 5 <[email protected]>

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

@@ -8,7 +8,7 @@ As of 20 September 2026, the working branch is `plugin/host-model-api` at
 `a8dd3640` plus the Leader increment, published as draft PR
 [#1391](https://github.com/HakanSeven12/OpenCADStudio/pull/1391). Host API is
 v7. The Python feature has explicit writes for **37 of 43** canvas kinds: 36
-are creatable (the legacy `Polyline` is update-only) and `Insert` remains update-only. This is **not** 37 completed
+are creatable (the legacy `Polyline` is update-only). This is **not** 37 completed
 kinds: Tolerance, Shape, AttributeEntity, Hatch, MLine, Dimension, MultiLeader, Table, PolygonMesh, PolyfaceMesh, Mesh, Wipeout, Point, Line, Circle, Arc, Ellipse, LwPolyline, Text, MText, Ray, XLine, Solid and Face3D pass every completion gate; Insert now passes every gate too; the audited Polyline (update-only by decision), Polyline2D, Polyline3D and Spline pass every gate that their format allows.
 AttributeDefinition passes its host and real IPC lifecycle but remains short of
 `Complete` because the previously pinned CAD codec dropped optional ATTDEF

docs/plugin-host-model.md

@@ -50,10 +50,11 @@ The bundled first-party adapter under `plugins/opencad-python` currently maps
 these entity kinds to Python dictionaries: Point, Line, Circle, Arc, Ellipse,
 Polyline, Polyline2D, Polyline3D, LwPolyline, Spline, Text, MText, Ray, XLine,
 Solid, Face3D, Insert, Tolerance, Shape, AttributeDefinition,
-AttributeEntity, and Hatch. Insert is update-only: the block name is readable
-but cannot be changed, and Python creation is withheld until block-table
-references can be established safely. Attached attributes remain available in
-the raw snapshot. The authoritative per-field mapping is
+AttributeEntity, and Hatch. An Insert is created by naming an existing
+ordinary block (the host refuses unknown blocks, model or paper space and
+containment cycles); the block name cannot be changed afterwards. Attached
+attributes stay with the AttributeEntity flow and remain in the raw snapshot.
+The legacy Polyline is update-only: create a Polyline2D or Polyline3D. The authoritative per-field mapping is
 `plugins/opencad-python/entity_manifest.json`. The generated
 mapping excludes fields it cannot represent, including common color, line
 weight, transparency, Polyline3D smooth type, and MText background color.