Input field background renders black with near-invisible text (low contrast) mid-session

Describe the bug

Mid-session, only the command input field's background turned black, making typed text nearly invisible against it. The rest of the terminal/session output rendered normally and was unaffected. A standard terminal  reset  did not fix it, indicating the issue is in the CLI's own TUI rendering rather than a terminal-level escape sequence leak.

Affected version

Copilot CLI version: 1.0.81

Steps to reproduce the behavior

1. Run  copilot  inside a tmux session (TERM=tmux-256color).
2. Use the CLI normally for a while (no manual  /theme  change).
3. Observe the input field's background suddenly turns black with low-contrast/invisible text, while surrounding output text stays normal.
4. Run  reset  in the terminal — input field remains black.

Expected behavior

Input field should maintain consistent theme-appropriate contrast for the whole session.

Additional context

Suspected cause: Theme/color-mode detection or caching bug specific to tmux ( TERM=tmux-256color ), possibly triggered by a state change during the session (resize, mode switch, subagent/tool output, etc.).

首先，在 TERM=tmux-256color 的 tmux 中的 copilot 里复现该问题，然后观察列出的各种可能会话变化中的 theme 或 color-mode 行为。当只有输入字段变黑时，跟踪 CLI TUI 的渲染状态，并验证该字段在整个会话期间以及运行 reset 后都保持适合 theme 的对比度。