Up/Down arrow keys no longer move cursor to beginning/end of input (regression since ~2.1.172)

Description

Up/Down arrow keys in the chat input no longer move the cursor to the beginning (Up) or end (Down) of the prompt text. This was a convenient shortcut for quickly navigating within a single-line or short prompt in version 2.1.89.

Environment

• OS: Windows 11
• Claude Code version with issue: latest (2.1.172+)
• Claude Code version without issue: 2.1.89
• Model: Opus 4.6 [1m]

Steps to Reproduce

1. Type a prompt in the chat input
2. Place cursor in the middle of the text
3. Press Up arrow — expect cursor to jump to the beginning of the input
4. Press Down arrow — expect cursor to jump to the end of the input

Expected Behavior (as in 2.1.89)

• Up arrow: moves cursor to the beginning of the input text
• Down arrow: moves cursor to the end of the input text

Actual Behavior

Up/Down arrow keys do not move the cursor to beginning/end of input. They may trigger history navigation or do nothing instead.

Notes

• This is a regression from 2.1.89 behavior.
• Release notes for 2.1.160 mention: "Fixed Up/Down arrows jumping to command history past the wrapped rows of a long input line — they now move through each visual row first, and history recall enters at the near edge" — this change likely altered the previous behavior where Up/Down acted as Home/End on single-line inputs.
• Ctrl+A / Ctrl+E (readline) exist as alternatives, but the Up/Down shortcut was faster for quick edits.