[BUG] Input background highlighting appears inconsistently

Bug Description

The background color/highlighting of user input in the Claude Code CLI appears inconsistently - sometimes the input area has a highlighted background, and sometimes it does not. This happens without any apparent pattern or user action.

Environment

• Claude Code Version: 2.0.69
• OS: macOS
• Terminal: (Standard macOS terminal)
• Shell: fish

Steps to Reproduce

1. Start Claude Code
2. Use the CLI normally
3. Observe that the input background highlighting sometimes appears and sometimes doesn't

Expected Behavior

The input background highlighting should be consistent - either always present or always absent.

Actual Behavior

The input background highlighting appears intermittently/inconsistently.

Screenshots

(Screenshot to be attached in comments)

Possibly Related Issues

• #8504 - Disable or Customize User Input Background Highlighting
• #12910 - OSC terminal color query responses leak into input buffer