Remap dimension associations across a copy

COPY, MIRROR and ARRAY duplicated a dimension's baked block but left the
copy with no association at all. Now a copy keeps one, on one condition:
every handle in every chain — the viewport, each INSERT on the block
path, the source entity, and an intersection's second chain — must have
been copied too. Then the whole chain is remapped onto the copies, so
the copy measures the copied geometry.

The condition is all-or-nothing on purpose. A partially-remapped chain
would leave a copy quietly driven by the original's geometry, which is
worse than no association; and copying a dimension on its own still
produces an unassociated dimension, which is exactly what the model
space path did before. It is the same rule `copy_complete_groups` uses
for groups, applied to a longer chain.

Co-Authored-By: Claude Fable 5.1 <[email protected]>

src/scene/modify.rs

@@ -744,6 +744,11 @@ impl Scene {
         // Complete group copies record their new Group objects and dictionary
         // entry as targeted object deltas inside copy_complete_groups.
         self.copy_complete_groups(&handle_map);
+        // A dimension copied together with everything it measures (its
+        // viewport, its block path and its source) keeps an association, with
+        // every handle remapped onto the copies. Copied on its own it keeps
+        // none — see `copy_dimension_associations`.
+        self.copy_dimension_associations(&handle_map);
         // The copies are new handles (natural memo misses, tessellated fresh)
         // and reference only already-cached blocks — no block defn changes.
         // Report them as additions so derived caches patch in exactly the copies.