chore: mark fill_tris_low unpaired sites with FIXME

dimension.rs (x2), multileader.rs (x3), table.rs (x1) emit fill_tris
without a corresponding fill_tris_low. These will trip the debug_assert_eq!
added in the preceding commit when the entity appears inside a block
definition. Each site is marked with a FIXME referencing block_cache.rs:1397
and the correct fix pattern (split_ds on each vertex).

src/entities/dimension.rs

@@ -1261,6 +1261,9 @@ fn tessellate_dimension_inner(
         plinegen: true,
         vp_scissor: None,
         fill_tris: geom.arrow_fill,
+        // FIXME: fill_tris_low left empty — needs double-single split to match
+        // fill_tris. Any geometry from this path inside a block definition will
+        // trip the debug_assert_eq! in emit_wire (block_cache.rs:1397).
         fill_tris_low: Vec::new(),
     });
 
@@ -1293,8 +1296,11 @@ fn tessellate_dimension_inner(
                     aabb: WireModel::UNBOUNDED_AABB,
                     plinegen: true,
                     vp_scissor: None,
-                    fill_tris: rect,
+        fill_tris: rect,
-                    fill_tris_low: Vec::new(),
+        // FIXME: fill_tris_low left empty — needs double-single split to match
+        // fill_tris. Any geometry from this path inside a block definition will
+        // trip the debug_assert_eq! in emit_wire (block_cache.rs:1397).
+        fill_tris_low: Vec::new(),
                 });
             }
         }

src/entities/multileader.rs

@@ -1304,6 +1304,9 @@ impl MultiLeaderTess for MultiLeader {
             plinegen: true,
             vp_scissor: None,
             fill_tris: arrow_fill,
+            // FIXME: fill_tris_low left empty — needs double-single split to match
+            // fill_tris. Any geometry from this path inside a block definition will
+            // trip the debug_assert_eq! in emit_wire (block_cache.rs:1397).
             fill_tris_low: Vec::new(),
         });
 
@@ -1593,6 +1596,9 @@ impl MultiLeaderTess for MultiLeader {
                         plinegen: true,
                         vp_scissor: None,
                         fill_tris: greek_tris,
+                        // FIXME: fill_tris_low left empty — needs double-single split to match
+                        // fill_tris. Any geometry from this path inside a block definition will
+                        // trip the debug_assert_eq! in emit_wire (block_cache.rs:1397).
                         fill_tris_low: Vec::new(),
                     });
                 }
@@ -1670,6 +1676,9 @@ impl MultiLeaderTess for MultiLeader {
                         plinegen: true,
                         vp_scissor: None,
                         fill_tris: text_fill_tris,
+                        // FIXME: fill_tris_low left empty — needs double-single split to match
+                        // fill_tris. Any geometry from this path inside a block definition will
+                        // trip the debug_assert_eq! in emit_wire (block_cache.rs:1397).
                         fill_tris_low: Vec::new(),
                     });
                 }

src/entities/table.rs

@@ -755,6 +755,9 @@ pub fn tessellate_table(
                 plinegen: true,
                 vp_scissor: None,
                 fill_tris,
+                // FIXME: fill_tris_low left empty — needs double-single split to match
+                // fill_tris. Any geometry from this path inside a block definition will
+                // trip the debug_assert_eq! in emit_wire (block_cache.rs:1397).
                 fill_tris_low: Vec::new(),
             }
         };