fix(blocks): block_explode keeps attribute text as TEXT (BURST rule) on both engines

virtual_entities() yields geometry only, so an exploded tagged symbol lost
its tag value silently. Every attached ATTRIB now becomes a TEXT at the
same WCS placement/height/rotation/style/layer (invisible stays
invisible), reported as attribute_texts. COM reads GetAttributes before
Explode, deletes the ATTDEF placeholders Explode returns, AddText per
value, and deletes the reference ActiveX Explode leaves behind.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FKFStjEFzpGyLq5bMpWxTd

server.py

@@ -3026,7 +3026,17 @@ async def block_explode(
     handle: Annotated[str, "Block reference (INSERT) entity handle"],
     ctx: Context = None,
 ) -> dict:
-    """Explode a block reference into its individual component entities."""
+    """Explode a block reference into its component entities, keeping its
+    attribute text (the Express Tools BURST rule, on both engines).
+
+    Every attached ATTRIB becomes a TEXT with the same value, placement,
+    height, rotation and layer (an invisible attribute becomes an invisible
+    TEXT); AutoCAD's plain EXPLODE would keep only the tag-name placeholders
+    and drop the values. Returns `inserted_handles` (the geometry),
+    `attribute_texts` (one TEXT handle per attribute), `exploded_handle` and
+    `backend`. Refused: a handle that is not a block reference (nothing is
+    written). Not undoable except through `drawing_undo` / a transaction.
+    """
     await ctx.warning(f"Exploding block reference {handle}")
     return await _backend(ctx).block_explode(handle)