Numpad Enter outputs raw CSI u sequence (57414u) in cmux/Ghostty — regression in 2.1.84

Bug Description

Numpad Enter key outputs 7414u (the tail end of the CSI u escape sequence ^[[57414u) instead of registering as Enter. Main Enter key works correctly. This appears to be a regression in Claude Code 2.1.84.

Environment

• Claude Code version: 2.1.84
• Terminal: cmux 0.62.2 (Ghostty-based, TERM=xterm-ghostty)
• OS: macOS (Darwin 25.4.0, MacBook Pro M3 Max)
• Keyboard: NuPhy Air96 V2 — confirmed working correctly via VIA test mode (both Enter keys register correct keycodes)

Steps to Reproduce

1. Open Claude Code in cmux terminal
2. Type any text
3. Press numpad Enter (KP_Enter)
4. Observe 7414u appended to input instead of submit

Expected Behaviour

Numpad Enter should submit input, identical to main Enter.

Actual Behaviour

Raw CSI u sequence characters 7414u are inserted as text. The full sequence ^[[57414u is being sent by the terminal (Kitty keyboard protocol encoding for KP_Enter, codepoint 57414) but Claude Code is not interpreting it.

Context

• This was not happening prior to 2.1.84. The user has been using cmux daily for over a week with no issues.
• 2.1.84 also fixed a separate issue with spacebar/voice input, suggesting the keyboard protocol negotiation changed in this release.
• The keyboard is confirmed innocent — VIA test mode shows correct keycodes for both Enter keys.
• This is purely a Claude Code ↔ Kitty keyboard protocol handling issue, not a terminal or hardware bug.

Related Issues

• #17040 (closed as inactive)
• #18480 (closed as duplicate of #17040)
• #17386 (similar CSI u issue in iTerm2)

Both prior issues were auto-closed without a fix. This is a fresh regression in 2.1.84.

Workaround

Use the main Enter key instead of numpad Enter. No terminal-side fix is available — cmux doesn't support custom keybindings yet (manaflow-ai/cmux#135).