Fix up/down arrow regression and add test. (google-gemini#18108)

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Author: jacob314

packages/cli/src/ui/components/shared/text-buffer.test.ts

@@ -1384,6 +1384,61 @@ describe('useTextBuffer', () => {
       expect(state.visualCursor).toEqual([0, 1]);
     });
 
+    it('move: up/down should work on wrapped lines (regression test)', () => {
+      // Line that wraps into two visual lines
+      // Viewport width 10. "0123456789ABCDE" (15 chars)
+      // Visual Line 0: "0123456789"
+      // Visual Line 1: "ABCDE"
+      const { result } = renderHook(() =>
+        useTextBuffer({
+          viewport: { width: 10, height: 5 },
+          isValidPath: () => false,
+        }),
+      );
+
+      act(() => {
+        result.current.setText('0123456789ABCDE');
+      });
+
+      // Cursor should be at the end: logical [0, 15], visual [1, 5]
+      expect(getBufferState(result).cursor).toEqual([0, 15]);
+      expect(getBufferState(result).visualCursor).toEqual([1, 5]);
+
+      // Press Up arrow - should move to first visual line
+      // This currently fails because handleInput returns false if cursorRow === 0
+      let handledUp = false;
+      act(() => {
+        handledUp = result.current.handleInput({
+          name: 'up',
+          shift: false,
+          alt: false,
+          ctrl: false,
+          cmd: false,
+          insertable: false,
+          sequence: '\x1b[A',
+        });
+      });
+      expect(handledUp).toBe(true);
+      expect(getBufferState(result).visualCursor[0]).toBe(0);
+
+      // Press Down arrow - should move back to second visual line
+      // This would also fail if cursorRow is the last logical row
+      let handledDown = false;
+      act(() => {
+        handledDown = result.current.handleInput({
+          name: 'down',
+          shift: false,
+          alt: false,
+          ctrl: false,
+          cmd: false,
+          insertable: false,
+          sequence: '\x1b[B',
+        });
+      });
+      expect(handledDown).toBe(true);
+      expect(getBufferState(result).visualCursor[0]).toBe(1);
+    });
+
     it('moveToVisualPosition: should correctly handle wide characters (Chinese)', () => {
       const { result } = renderHook(() =>
         useTextBuffer({

packages/cli/src/ui/components/shared/text-buffer.ts

@@ -2905,12 +2905,12 @@ export function useTextBuffer({
         return true;
       }
       if (keyMatchers[Command.MOVE_UP](key)) {
-        if (cursorRow === 0) return false;
+        if (visualCursor[0] === 0) return false;
         move('up');
         return true;
       }
       if (keyMatchers[Command.MOVE_DOWN](key)) {
-        if (cursorRow === lines.length - 1) return false;
+        if (visualCursor[0] === visualLines.length - 1) return false;
         move('down');
         return true;
       }
@@ -2990,6 +2990,8 @@ export function useTextBuffer({
       singleLine,
       setText,
       text,
+      visualCursor,
+      visualLines,
     ],
   );