feat(dimstyle): block/linetype Handle cyclers for arrowheads & ext lines

The arrowhead-block (DIMBLK/DIMBLK1/DIMBLK2/DIMLDRBLK) and ext-line
linetype (DIMLTYPE/DIMLTEX1/DIMLTEX2) Handle fields are now editable in
the Dimension Style manager. Each shows the resolved block-record /
linetype name and a Cycle button that advances through the available
records (NULL = Default arrowhead / ByBlock linetype). Edits bump
geometry so dimensions re-render with the new arrowheads/linetypes.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/mod.rs

@@ -1071,6 +1071,9 @@ pub enum Message {
     // Field edit messages:
     DsEdit(DsField, String),
     DsToggle(DsField),
+    /// Cycle a block/linetype Handle field on the selected dim style to the
+    /// next available block-record / linetype.
+    DsCycleHandle(&'static str),
     // ── Raster Image ──────────────────────────────────────────────────────
     /// Open file-picker dialog for IMAGE command (async).
     ImagePick,

src/app/update.rs

@@ -6534,6 +6534,53 @@ impl OpenCADStudio {
                 self.apply_ds_toggle(field);
                 Task::none()
             }
+            Message::DsCycleHandle(field) => {
+                let i = self.active_tab;
+                let name = self.dimstyle_selected.clone();
+                let is_lt = matches!(
+                    field,
+                    "dimltex_handle" | "dimltex1_handle" | "dimltex2_handle"
+                );
+                let doc = &self.tabs[i].scene.document;
+                let mut candidates: Vec<acadrust::types::Handle> =
+                    vec![acadrust::types::Handle::NULL];
+                if is_lt {
+                    candidates.extend(doc.line_types.iter().map(|lt| lt.handle));
+                } else {
+                    candidates.extend(doc.block_records.iter().map(|b| b.handle));
+                }
+                let Some(ds) = doc.dim_styles.get(&name) else {
+                    return Task::none();
+                };
+                let cur = match field {
+                    "dimblk" => ds.dimblk,
+                    "dimblk1" => ds.dimblk1,
+                    "dimblk2" => ds.dimblk2,
+                    "dimldrblk" => ds.dimldrblk,
+                    "dimltex_handle" => ds.dimltex_handle,
+                    "dimltex1_handle" => ds.dimltex1_handle,
+                    "dimltex2_handle" => ds.dimltex2_handle,
+                    _ => return Task::none(),
+                };
+                let idx = candidates.iter().position(|h| *h == cur).unwrap_or(0);
+                let next = candidates[(idx + 1) % candidates.len()];
+                self.push_undo_snapshot(i, "DIMSTYLE EDIT");
+                if let Some(ds) = self.tabs[i].scene.document.dim_styles.get_mut(&name) {
+                    match field {
+                        "dimblk" => ds.dimblk = next,
+                        "dimblk1" => ds.dimblk1 = next,
+                        "dimblk2" => ds.dimblk2 = next,
+                        "dimldrblk" => ds.dimldrblk = next,
+                        "dimltex_handle" => ds.dimltex_handle = next,
+                        "dimltex1_handle" => ds.dimltex1_handle = next,
+                        "dimltex2_handle" => ds.dimltex2_handle = next,
+                        _ => {}
+                    }
+                }
+                self.tabs[i].dirty = true;
+                self.tabs[i].scene.bump_geometry();
+                Task::none()
+            }
         }
     }
 }

src/app/view.rs

@@ -234,6 +234,50 @@ impl OpenCADStudio {
                 .iter()
                 .map(|s| s.name.clone())
                 .collect();
+            let doc = &tab.scene.document;
+            let blk_name = |h: acadrust::types::Handle| -> String {
+                if h.is_null() {
+                    "Default".to_string()
+                } else {
+                    doc.block_records
+                        .iter()
+                        .find(|b| b.handle == h)
+                        .map(|b| b.name.trim_start_matches('_').to_string())
+                        .unwrap_or_else(|| "?".to_string())
+                }
+            };
+            let lt_name = |h: acadrust::types::Handle| -> String {
+                if h.is_null() {
+                    "ByBlock".to_string()
+                } else {
+                    doc.line_types
+                        .iter()
+                        .find(|lt| lt.handle == h)
+                        .map(|lt| lt.name.clone())
+                        .unwrap_or_else(|| "?".to_string())
+                }
+            };
+            let ds_sel = doc.dim_styles.get(&self.dimstyle_selected);
+            let (
+                dimblk_name,
+                dimblk1_name,
+                dimblk2_name,
+                dimldrblk_name,
+                dimltex_name,
+                dimltex1_name,
+                dimltex2_name,
+            ) = match ds_sel {
+                Some(d) => (
+                    blk_name(d.dimblk),
+                    blk_name(d.dimblk1),
+                    blk_name(d.dimblk2),
+                    blk_name(d.dimldrblk),
+                    lt_name(d.dimltex_handle),
+                    lt_name(d.dimltex1_handle),
+                    lt_name(d.dimltex2_handle),
+                ),
+                None => Default::default(),
+            };
             return crate::ui::dimstyle::view_window(
                 styles,
                 &self.dimstyle_selected,
@@ -308,6 +352,13 @@ impl OpenCADStudio {
                     dimalttz: &self.ds_dimalttz,
                     dimtolj: &self.ds_dimtolj,
                     dimtzin: &self.ds_dimtzin,
+                    dimblk_name,
+                    dimblk1_name,
+                    dimblk2_name,
+                    dimldrblk_name,
+                    dimltex_name,
+                    dimltex1_name,
+                    dimltex2_name,
                 },
             );
         }