Complete MultiLeader host model coverage

Extends the adapter generator (Color, LineWeight, mixed unit/payload enums,
fixed float arrays, bitflags-2 newtypes, keep_types override) and maps
MultiLeader with a merge-style context patch, host validation and
reference checks. staged_python_multileader_lifecycle_over_real_ipc passes
the full gate including DWG and DXF reopen.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

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

@@ -7,13 +7,13 @@ Build a general Python document model over the OCS host API for all **43 canvas
 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 **25 of 43** canvas kinds: 24
-are creatable and `Insert` remains update-only. This is **not** 25 completed
-kinds: Tolerance, Shape, AttributeEntity, Hatch, MLine and Dimension pass every completion gate.
+v7. The Python feature has explicit writes for **26 of 43** canvas kinds: 25
+are creatable and `Insert` remains update-only. This is **not** 26 completed
+kinds: Tolerance, Shape, AttributeEntity, Hatch, MLine, Dimension and MultiLeader pass every completion gate.
 AttributeDefinition passes its host and real IPC lifecycle but remains short of
 `Complete` because the previously pinned CAD codec dropped optional ATTDEF
 fields during DXF reads; revalidate that blocker against the current
-`acadrust` revision `7ea4247`. Leader is mapped and integration-tested but blocked at W by three acadrust persistence gaps (see the ledger). The other 18 canvas kinds have only `layer`
+`acadrust` revision `7ea4247`. Leader is mapped and integration-tested but blocked at W by three acadrust persistence gaps (see the ledger). The other 17 canvas kinds have only `layer`
 writes through the document model. All 43 have raw typed snapshots. There are
 three internal records and two opaque fallbacks outside the 43 canvas kinds.
 
@@ -123,7 +123,7 @@ The last five may require new engine capabilities rather than only Python conver
 
 ## Handoff start point
 
-Continue with **MultiLeader** (queue item 4). Leader is done except for its W
+Continue with **Table** (queue item 5). Leader is done except for its W
 gate; when the engine writes DXF group 340, reads group 213 and the DWG
 R2010+ text-size question is decided, flip the canary assertions in
 `staged_python_leader_lifecycle_over_real_ipc` and mark it `Complete`.
@@ -160,3 +160,4 @@ exact queue above and update statuses with evidence after each increment.
 - Mapped `Leader` (host validation and reference binding in `entity_coverage.rs`, policy/build.rs/manifest entries, adapter count 23). `staged_python_leader_lifecycle_over_real_ipc` passes C/R/E/D/U/I/V/P through the real runner. W is blocked by acadrust: the DXF writer omits the annotation handle (340), DXF reads lose `annotation_offset` (213), and DWG R2010+ does not store text size or hookline flag. Each gap is pinned by a canary assertion so it fails loudly once fixed. The queue now continues with `MLine`.
 - Completed `MLine`. Host validation and style binding live in `ocs_plugin_api`; derived vertex geometry and element parameters are recomputed by the host (`normalize_scripted_mline`) on scripted create/edit, so scripts supply positions only. The adapter maps `flags` as an integer through a manifest override because the generator cannot classify acadrust's serde-newtype `MLineFlags`. `staged_python_mline_lifecycle_over_real_ipc` passes C/R/E/D/U/I/W/V/P with DWG and DXF reopen. The queue now continues with `Dimension`.
 - Completed `Dimension` for all nine subtypes. Because the payload is an enum, the adapter generator gained a `manual_kinds` hook (hand-written `<kind>_to_dict/_from_dict/_apply`) and the host catalog a `synthetic` policy section. The host derives `actual_measurement` and the base definition point on every scripted create/edit. Python ints are now accepted wherever a coordinate or angle is expected. `staged_python_dimension_lifecycle_over_real_ipc` records each subtype separately and all nine pass C/R/E/D/U/I/W/V/P. The queue now continues with `MultiLeader`.
+- Completed `MultiLeader`. The adapter generator now converts `Color`, `LineWeight`, mixed unit/payload enums, fixed float arrays and bitflags-2 newtypes, and a `keep_types` override lets a hand-written setter reuse generated converters (used for the merge-style `context` patch). `Leader.override_color` became writable through the same `Color` form; neither file format stores it. `staged_python_multileader_lifecycle_over_real_ipc` passes the full gate with DWG and DXF reopen. The queue now continues with `Table`.