feat(props): make dim-line colour editable for leaders and dimensions

The "Dim line color" row on Leader and Dimension entities was
read-only: an earlier attempt wired it to Leader.override_color, which
acadrust never serialises, so the pick was lost on save. Store it
instead as a standard ACAD_DSTYLE per-object dimension-style override
(DXF code 176, an ACI index) through the existing dim_override codec,
so it round-trips through both DWG and DXF like the other dim
overrides. RGB picks collapse to the nearest ACI, matching the rest of
the dim-colour stack (dimension styles are index-only through the file
layer). The renderer prefers the override over the style's DIMCLRD.

The write branch is guarded to leaders and dimensions so a mixed
selection cannot stamp the override onto other entity types.

Bumps acadrust to c9fe982, which carries parsed XDATA onto dimensions
on DXF read (it was dropping common.extended_data), so the dimension
override persists on DXF save as well as DWG.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

src/entities/dim_override.rs

@@ -6,6 +6,7 @@
 //! renderer and the properties panel prefer an override over the style default,
 //! so editing one of these rows writes here and the change round-trips to file.
 
+use acadrust::types::Color;
 use acadrust::xdata::{ExtendedData, XDataValue};
 use acadrust::{CadDocument, Handle};
 
@@ -13,6 +14,7 @@ use acadrust::{CadDocument, Handle};
 pub const DIMSCALE: i16 = 40; // overall scale       (real)
 pub const DIMASZ: i16 = 41; // arrow size          (real)
 pub const DIMTAD: i16 = 77; // text vertical pos   (int16)
+pub const DIMCLRD: i16 = 176; // dim line colour     (int16 = ACI index)
 pub const DIMGAP: i16 = 147; // text offset / gap   (real)
 pub const DIMLWD: i16 = 371; // dim line lineweight (int16)
 pub const DIMLDRBLK: i16 = 341; // leader arrow block  (handle)
@@ -58,6 +60,13 @@ pub fn int(xd: &ExtendedData, code: i16) -> Option<i16> {
         })
 }
 
+/// The colour override for `code`, if present. Dim-colour overrides are stored
+/// as an ACI index (the same `int16` slot the dimension style uses), so this
+/// decodes it back into a `Color` (0 = ByBlock, 256 = ByLayer, else indexed).
+pub fn color(xd: &ExtendedData, code: i16) -> Option<Color> {
+    int(xd, code).map(Color::from_index)
+}
+
 /// The handle-valued override for `code`, if present.
 pub fn handle(xd: &ExtendedData, code: i16) -> Option<Handle> {
     pairs(xd)

src/entities/dimension.rs

@@ -1290,11 +1290,18 @@ fn tessellate_dimension_inner(
     );
 
     // Per-spec colours: DIMCLRD (dim/arrows), DIMCLRE (ext), DIMCLRT (text).
-    // 0=ByBlock and 256=ByLayer fall through to entity_color.
+    // 0=ByBlock and 256=ByLayer fall through to entity_color. DIMCLRD also
+    // honours a per-object ACAD_DSTYLE override (code 176) so an edited
+    // dim-line colour renders even without touching the style.
     let dim_color = if selected {
         WireModel::SELECTED
     } else {
-        resolve_dim_color(style.map(|s| s.dimclrd).unwrap_or(0), entity_color)
+        let dim_clr = crate::entities::dim_override::int(
+            &dim.base().common.extended_data,
+            crate::entities::dim_override::DIMCLRD,
+        )
+        .unwrap_or_else(|| style.map(|s| s.dimclrd).unwrap_or(0));
+        resolve_dim_color(dim_clr, entity_color)
     };
     let ext_color = if selected {
         WireModel::SELECTED

src/entities/leader.rs

@@ -547,10 +547,29 @@ impl LeaderTess for Leader {
         use crate::entities::dim_override as dov;
         use crate::scene::model::wire_model::WireModel;
         let xd = &self.common.extended_data;
+        // Dim-line colour: a per-object ACAD_DSTYLE override (code 176, an ACI
+        // index) wins over the assigned dim style's DIMCLRD; ByLayer / ByBlock
+        // (0 / 256) and no setting fall through to the entity colour.
         let color = if selected {
             WireModel::SELECTED
         } else {
-            entity_color
+            let dim_clr = dov::int(xd, dov::DIMCLRD).or_else(|| {
+                document
+                    .dim_styles
+                    .iter()
+                    .find(|s| {
+                        s.name.eq_ignore_ascii_case(&self.dimension_style)
+                            || (self.dimension_style.trim().is_empty()
+                                && s.name.eq_ignore_ascii_case("Standard"))
+                    })
+                    .map(|s| s.dimclrd)
+            });
+            match dim_clr {
+                Some(idx) if idx != 0 && idx != 256 => crate::scene::convert::tess_util::aci_to_rgba(
+                    &acadrust::types::Color::from_index(idx),
+                ),
+                _ => entity_color,
+            }
         };
         // A concrete DIMLWD override sets the leader line's weight; ByLayer /
         // ByBlock / Default and no override keep the resolved weight passed in.