cmd+backspace in multi-line chat input deletes all lines instead of current line

Description

When the chat input contains multiple lines, pressing cmd+backspace deletes the entire input (all lines) instead of only the current line, which is the standard macOS behavior in virtually every other text input.

Expected behavior

cmd+backspace should delete only the current line (from cursor to start of line), matching native macOS text editing conventions.

Actual behavior

cmd+backspace clears the entire multi-line input, wiping work from other lines.

Steps to reproduce

1. Open Claude Code in a macOS terminal
2. In the chat input, type several lines (use ctrl+j for newlines)
3. Place cursor on one of the lines
4. Press cmd+backspace
5. Observe that all lines are deleted, not just the current one

Workaround

None via keybindings — the available chat actions only include chat:clearInput (full clear), with no line-level delete primitive to remap.

Environment

• macOS (Darwin 25.2.0)
• Shell: zsh
• Claude Code CLI