fix(core): correct ellipsis logic in EditTool getDescription()

The description snippet for old_string and new_string was using
the total string length to decide whether to append '...' instead
of checking the first-line length that was actually being displayed.

This caused two issues:
- Multi-line strings with a short first line (< 30 chars) would not
  show '...' even though the edit description was only showing the
  first line, hiding that the edit spans multiple lines.
- The check was inconsistent: substring(0, 30) was applied on the
  first line, but the length guard was on the entire string.

Fix by extracting the first line into a variable and checking:
1. Whether the first line itself exceeds 30 characters (truncated by
   substring), OR
2. Whether the full string is multi-line (\n present), indicating
   more content exists beyond what is shown.

Added unit tests to cover all cases: new file, short single-line,
multi-line with short first line, long first line, and no-op edits.

Author: Megashubham

packages/core/src/tools/edit.test.ts

@@ -703,6 +703,79 @@ function doIt() {
     });
   });
 
+  describe('getDescription', () => {
+    it('should return "Create <path>" for new file (empty old_string)', () => {
+      const filePath = path.join(rootDir, 'new.ts');
+      const params: EditToolParams = {
+        file_path: filePath,
+        instruction: 'Create new file',
+        old_string: '',
+        new_string: 'content',
+      };
+      const invocation = tool.build(params);
+      expect(invocation.getDescription()).toMatch(/^Create /);
+    });
+
+    it('should NOT append "..." to a short single-line old_string and new_string', () => {
+      const filePath = path.join(rootDir, 'test.ts');
+      const params: EditToolParams = {
+        file_path: filePath,
+        instruction: 'Replace short old with short new',
+        old_string: 'short old',
+        new_string: 'short new',
+      };
+      const invocation = tool.build(params);
+      const description = invocation.getDescription();
+      expect(description).toContain('short old');
+      expect(description).toContain('short new');
+      expect(description).not.toMatch(/short old\.\.\./);
+      expect(description).not.toMatch(/short new\.\.\./);
+    });
+
+    it('should append "..." when old_string or new_string is multi-line, even if first line is short', () => {
+      const filePath = path.join(rootDir, 'test.ts');
+      // old_string first line is only 17 chars (< 30), but the full string is multi-line
+      const params: EditToolParams = {
+        file_path: filePath,
+        instruction: 'Replace function foo with bar',
+        old_string: 'function foo() {\n  return 1;\n}',
+        new_string: 'function bar() {\n  return 2;\n}',
+      };
+      const invocation = tool.build(params);
+      const description = invocation.getDescription();
+      // First lines are short, but since strings are multi-line, '...' should appear
+      // The full first line 'function foo() {' is kept (17 chars < 30) and '...' is appended
+      expect(description).toContain('function foo() {...');
+      expect(description).toContain('function bar() {...');
+    });
+
+    it('should append "..." when the first line of old_string exceeds 30 characters', () => {
+      const filePath = path.join(rootDir, 'test.ts');
+      const longFirstLine = 'a'.repeat(35); // 35 chars, exceeds 30
+      const params: EditToolParams = {
+        file_path: filePath,
+        instruction: 'Replace long line',
+        old_string: longFirstLine,
+        new_string: 'short',
+      };
+      const invocation = tool.build(params);
+      const description = invocation.getDescription();
+      expect(description).toContain('...');
+    });
+
+    it('should return "No file changes" when old_string equals new_string', () => {
+      const filePath = path.join(rootDir, 'test.ts');
+      const params: EditToolParams = {
+        file_path: filePath,
+        instruction: 'No-op edit',
+        old_string: 'same content',
+        new_string: 'same content',
+      };
+      const invocation = tool.build(params);
+      expect(invocation.getDescription()).toMatch(/No file changes/);
+    });
+  });
+
   describe('execute', () => {
     const testFile = 'execute_me.txt';
     let filePath: string;

packages/core/src/tools/edit.ts

@@ -837,12 +837,18 @@ class EditToolInvocation
       return `Create ${shortenPath(relativePath)}`;
     }
 
-    const oldStringSnippet =
-      this.params.old_string.split('\n')[0].substring(0, 30) +
-      (this.params.old_string.length > 30 ? '...' : '');
-    const newStringSnippet =
-      this.params.new_string.split('\n')[0].substring(0, 30) +
-      (this.params.new_string.length > 30 ? '...' : '');
+    const getSnippet = (str: string): string => {
+      const newlineIdx = str.indexOf('\n');
+      const firstLine = newlineIdx !== -1 ? str.substring(0, newlineIdx) : str;
+      const chars = Array.from(firstLine);
+      if (chars.length > 30) {
+        return chars.slice(0, 30).join('') + '...';
+      }
+      return firstLine + (newlineIdx !== -1 ? '...' : '');
+    };
+
+    const oldStringSnippet = getSnippet(this.params.old_string);
+    const newStringSnippet = getSnippet(this.params.new_string);
 
     if (this.params.old_string === this.params.new_string) {
       return `No file changes to ${shortenPath(relativePath)}`;