fix(dimension): zero the group-12 insertion point on baked blocks (#181)

A dimension's *D block is baked in absolute WCS, so the DWG group-12
insertion point must be the origin. OCS's dimension commands seeded it
with the text anchor, so a reader that positions the block by that point
(BricsCAD / ODA) drew the dimension shifted by the offset, while OCS —
which renders the block in place — showed it correctly.

Reset base.insertion_point to the origin in bake_dimension_blocks, where
the absolute-WCS block is created. Only dimensions whose block OCS bakes
are touched; blocks preserved from other applications (baseline/continue
dimensions with a legitimate non-zero clone insertion) are left alone.

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

src/modules/draw/modify/explode.rs

@@ -1060,6 +1060,15 @@ pub fn bake_dimension_blocks(doc: &mut CadDocument) {
 
         if let Some(EntityType::Dimension(d)) = doc.get_entity_mut(handle) {
             d.base_mut().block_name = name;
+            // The block we just baked holds the dimension graphics in absolute
+            // WCS, so the DWG group-12 insertion point (base.insertion_point)
+            // MUST be the origin. A reader that positions the *D block by that
+            // point (BricsCAD / ODA) otherwise draws it shifted by the offset,
+            // while OCS — which renders the block in place — shows it correctly.
+            // OCS's dimension commands seed insertion_point with the text
+            // anchor; reset it here so the saved dimension lands identically in
+            // every application. (#181)
+            d.base_mut().insertion_point = Vector3::new(0.0, 0.0, 0.0);
         }
     }
 }
@@ -1136,6 +1145,36 @@ mod tests {
         );
     }
 
+    /// Baking a blockless dimension resets its group-12 insertion point to the
+    /// origin. OCS's commands seed it with the text anchor; left non-zero, a
+    /// reader that positions the absolute-WCS block by that point draws the
+    /// dimension shifted. Regression test for #181.
+    #[test]
+    fn bake_zeroes_insertion_point() {
+        let mut doc = CadDocument::new();
+
+        let mut d = DimensionLinear::new(Vector3::new(0.0, 0.0, 0.0), Vector3::new(10.0, 0.0, 0.0));
+        d.definition_point = Vector3::new(0.0, 5.0, 0.0);
+        d.base.text_middle_point = Vector3::new(5.0, 5.0, 0.0);
+        // Exactly what OCS-created dimensions carry: insertion == text anchor.
+        d.base.insertion_point = d.base.text_middle_point;
+        let handle = doc
+            .add_entity(EntityType::Dimension(Dimension::Linear(d)))
+            .unwrap();
+
+        bake_dimension_blocks(&mut doc);
+
+        let ins = match doc.get_entity(handle) {
+            Some(EntityType::Dimension(d)) => d.base().insertion_point,
+            _ => panic!("dimension missing"),
+        };
+        assert_eq!(
+            ins,
+            Vector3::new(0.0, 0.0, 0.0),
+            "baked dimension must carry a zero insertion point (#181)"
+        );
+    }
+
     // Collect the line segments baked into the dimension's `*D` block.
     fn baked_segments(doc: &CadDocument, block_name: &str) -> Vec<(Vector3, Vector3)> {
         let rec = doc.block_records.get(block_name).expect("block record");