feat(bedit): add Edit Block Definition dialog and new block authoring

Open the Edit Block Definition dialog when BEDIT is invoked without an active selection, listing candidate block definitions alphabetically while filtering layout records, anonymous blocks, and external references. Allow typing a new valid block name to start an empty block editor session that only commits to the drawing block table upon explicit save.

src/scene/block_service.rs

@@ -16,7 +16,7 @@
 use codec::objects::ObjectType;
 use codec::tables::BlockRecord;
 use codec::types::Handle;
-use codec::{CadDocument, EntityType};
+use codec::{CadDocument, EntityType, TableEntry};
 use std::collections::HashSet;
 use std::fmt;
 
@@ -285,6 +285,29 @@ fn is_layout_record(document: &CadDocument, record: &BlockRecord) -> bool {
         )
 }
 
+/// Candidate block names for the Edit Block Definition (BEDIT) dialog:
+/// excludes standard layouts (*MODEL_SPACE, *PAPER_SPACE), layout records,
+/// anonymous blocks (*U, *D, *T, etc.), and externally referenced blocks.
+/// Sorted alphabetically, case-insensitive.
+pub fn bedit_candidate_block_names(document: &CadDocument) -> Vec<String> {
+    let mut names: Vec<String> = document
+        .block_records
+        .iter()
+        .filter(|record| {
+            !record.is_standard()
+                && !is_layout_record(document, record)
+                && !record.is_anonymous()
+                && !record.name.starts_with('*')
+                && !record.flags.is_xref
+                && !record.flags.is_xref_overlay
+                && !record.name.contains('|')
+        })
+        .map(|record| record.name.clone())
+        .collect();
+    names.sort_by_key(|n| n.to_ascii_lowercase());
+    names
+}
+
 /// The extension-dictionary key on a dynamic block's record.
 const ENHANCED_BLOCK_KEY: &str = "ACAD_ENHANCEDBLOCK";
 
@@ -1238,4 +1261,32 @@ mod tests {
         assert!(would_create_cycle(&scene.document, "blockb", "BLOCKA"));
         assert!(!would_create_cycle(&scene.document, "blocka", "BLOCKB"));
     }
+
+    #[test]
+    fn locked_bedit_candidate_block_names_filters_and_sorts() {
+        let mut scene = scene();
+        define(&mut scene, "zebra");
+        define(&mut scene, "Alpha");
+        define(&mut scene, "Beta");
+
+        // Anonymous block
+        let mut anon = BlockRecord::new("*U1");
+        anon.handle = Handle::new(9901);
+        anon.flags.anonymous = true;
+        scene.document.block_records.add(anon).unwrap();
+
+        // Xref block
+        let mut xref = BlockRecord::new("XrefBlock");
+        xref.handle = Handle::new(9902);
+        xref.flags.is_xref = true;
+        scene.document.block_records.add(xref).unwrap();
+
+        // Xref dependent symbol
+        let mut xref_dep = BlockRecord::new("HOST|CHILD");
+        xref_dep.handle = Handle::new(9903);
+        scene.document.block_records.add(xref_dep).unwrap();
+
+        let candidates = bedit_candidate_block_names(&scene.document);
+        assert_eq!(candidates, vec!["Alpha", "Beta", "zebra"]);
+    }
 }