[BUG] Cmd+Delete and Ctrl+U delete entire buffer instead of line (regression since v2.1.100)

Summary

Since v2.1.100, both Cmd+Delete and Ctrl+U delete the entire multi-line prompt buffer instead of just the current line. Previously these were line-scoped.

Expected behavior

• Cmd+Delete — delete current line (macOS convention: delete to start of line)
• Ctrl+U — delete to start of line (readline convention, as in bash/zsh)

This matches Cmd+Arrow, which is line-scoped in Claude Code (moves line-by-line, not buffer start/end). The delete shortcuts should match the movement shortcuts.

Actual behavior

Both shortcuts wipe the entire prompt buffer. With no visible undo affordance, an accidental keypress destroys the whole in-progress prompt.

Impact

• Multi-line prompts (which Claude Code actively encourages) become risky to edit.
• Inconsistent with macOS / readline conventions that users have decades of muscle memory for.
• Inconsistent with Cmd+Arrow movement semantics inside Claude Code itself.
• Makes users want to compose prompts outside the terminal to avoid data loss.

Workaround / what's missing

• Ctrl+Y can restore the deleted content, but this isn't discoverable.
• There is no chat:deleteLine (or equivalent line-scoped) action in the keybindings system, so users can't rebind Cmd+Delete / Ctrl+U to the old behavior themselves.

Requests

1. Restore line-scoped behavior as the default for Cmd+Delete and Ctrl+U, or
2. Add a chat:deleteLine (and/or chat:deleteToLineStart) action so users can rebind via ~/.claude/keybindings.json.

Environment

• Claude Code version: v2.1.100+ (regression point per CHANGELOG)
• Platform: macOS (Darwin 24.6.0)