fix(cursor): improve cursor positioning logic for line breaks and diagnostics

- Implement special handling for BR elements in moveCursor
- Replace diagnostic ::before spacer with margin-left for better layout consistency
- Filter out diagnostic elements when calculating child index for cursor placement

Author: vipmax

anycode-base/src/cursor.ts

@@ -50,12 +50,32 @@ export function moveCursor(
         return
     }
 
-    const ch = chunk.firstChild || chunk;
+    // Special handling for BR elements: set cursor relative to parent, not inside BR
+    let ch: Node;
+    let chunkOffset: number;
+    
+    if (chunk.tagName === 'BR') {
+        // Find the index of the BR element within its parent
+        const parent = chunk.parentElement;
+        if (!parent) return;
+        
+        const childIndex = Array.from(parent.children)
+            .filter(child => !isDiagnosticElement(child))
+            .indexOf(chunk as Element);
+        
+        if (childIndex === -1) return;
+        
+        ch = parent;
+        chunkOffset = childIndex;
+    } else {
+        ch = chunk.firstChild || chunk;
+        chunkOffset = chunkCharacter;
+    }
 
     // Ensure we're working with the correct document context
     const doc = ch.ownerDocument || document;
     const range = doc.createRange();
-    range.setStart(ch, chunkCharacter);
+    range.setStart(ch, chunkOffset);
     range.collapse(true);
 
     // Check if the range is already the same as the current selection
@@ -86,8 +106,8 @@ export function moveCursor(
         const codePaddingLeft = codeElement ? 
             parseFloat(getComputedStyle(codeElement).paddingLeft) : 0;
 
-        const cursorNode = ch.firstChild || ch;
-        const cursorOffset = chunkCharacter;
+        const cursorNode = ch;
+        const cursorOffset = chunkOffset;
 
         scrollCursorIntoViewHorizontally(
             scrollable!, cursorNode, cursorOffset, 

anycode-base/src/styles.css

@@ -62,6 +62,7 @@
   color: #ff6b6b;
   border-radius: 4px;
   padding: 0 4px;
+  margin-left: 3ch;
   vertical-align: middle;
   line-height: 1;
   display: inline-block;
@@ -72,13 +73,6 @@
   cursor: text;
 }
 
-.diagnostic::before {
-  content: "";
-  display: inline-block;
-  width: 3ch;
-  pointer-events: none;
-}
-
 .code.selecting .diagnostic {
   user-select: none;
   -webkit-user-select: none;