Add link management: create, select, delete with undo/redo

Implement full link workflow between component slots on the wiresheet:
- Link Mark / Link From / Link To context menu items for creating links
- Link dialog with slot type validation and source/target swap button
- Selectable link wires (click to highlight in red) with right-click delete
- Undo/redo support for both add and delete link operations
- Component deletion already cascades to remove related links

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

sax_file.py

@@ -65,12 +65,15 @@ def reset_to_startup_state():
     app_state.current_sheet_parent = None
     app_state.selected_canvas_tag = None
     app_state.selected_tree_item_id = None
+    app_state.link_mark_element = None
+    app_state.selected_link_tag = None
 
     app_state.active_components_list.clear()
     app_state.tree_element_map.clear()
     app_state.canvas_comp_map.clear()
     app_state.canvas_tag_by_element.clear()
     app_state.component_slot_offsets.clear()
+    app_state.canvas_link_map.clear()
     app_state.final_components_registry.clear()
     app_state.active_schema_kits.clear()
 
@@ -423,6 +426,59 @@ def add_component(kit_name, type_name, grid_x, grid_y):
     return element
 
 
+def remove_link(link_element):
+    """Removes a <link> element from the <links> section and repaints."""
+    if app_state.xml_root_element is None:
+        return
+
+    links_elem = app_state.xml_root_element.find("links")
+    if links_elem is None:
+        return
+
+    try:
+        index = list(links_elem).index(link_element)
+        links_elem.remove(link_element)
+    except ValueError:
+        return
+
+    from_ref = link_element.get("from", "")
+    to_ref = link_element.get("to", "")
+    from_slot = from_ref.rsplit(".", 1)[-1] if "." in from_ref else from_ref
+    to_slot = to_ref.rsplit(".", 1)[-1] if "." in to_ref else to_ref
+    undo.push(undo.DeleteLinkCommand(
+        links_elem, index, link_element,
+        label=f"delete link {from_slot}→{to_slot}"
+    ))
+
+    app_state.selected_link_tag = None
+    app_state.mark_dirty()
+    wiresheet.render_current_sheet()
+
+
+def add_link(from_path_slot, to_path_slot):
+    """Adds a <link> element to the <links> section of the SAX DOM."""
+    if app_state.xml_root_element is None:
+        return
+
+    links_elem = app_state.xml_root_element.find("links")
+    if links_elem is None:
+        links_elem = ET.SubElement(app_state.xml_root_element, "links")
+
+    link_elem = ET.SubElement(links_elem, "link")
+    link_elem.set("from", from_path_slot)
+    link_elem.set("to", to_path_slot)
+
+    from_slot = from_path_slot.rsplit(".", 1)[-1] if "." in from_path_slot else from_path_slot
+    to_slot = to_path_slot.rsplit(".", 1)[-1] if "." in to_path_slot else to_path_slot
+    undo.push(undo.AddLinkCommand(
+        links_elem, link_elem,
+        label=f"add link {from_slot}→{to_slot}"
+    ))
+
+    app_state.mark_dirty()
+    wiresheet.render_current_sheet()
+
+
 def execute_cascading_deletion(comp_element):
     """Shared application logic to wipe an element, its children, and related links from DOM and runtime lists."""
     comp_name = comp_element.get("name", "Unknown")