Visual artifacts / "ghost" characters remain rendered in TUI after deleting text

### Describe the bug

When backspacing or deleting a text string within the Copilot CLI prompt, the visual interface fails to completely clear or redraw the terminal cells. Characters from the deleted text remain floating/rendered as visual artifacts (ghost characters) even though they are logically removed from the input buffer.

### Affected version

v1.0.65

### Steps to reproduce the behavior

1. Open Copilot CLI in a terminal emulator.

2. Type a long prompt or command string.

3. Use Backspace to rapidly delete or clear portions of the text.

Observe that sporadic characters from the original string remain statically rendered on the screen despite the cursor moving past or behind them.

### Expected behavior

When rapidly deleting character from a long prompt or command string there should not be any remaining "ghost" characters rendered.

### Additional context

_No response_

Reproduce the issue in Copilot CLI v1.0.65 using a long prompt, then rapidly delete text with Backspace in a terminal emulator. Trace the CLI's TUI input and terminal-cell redraw path, and verify that deleting text leaves no residual characters while the cursor moves through the prompt.

索引モデルが issue の本文から書いたものです。