[BUG] Shift+Enter newline regression in v2.1.91 (works in v2.1.87, Warp terminal)

Description

Shift+Enter no longer inserts a newline as of v2.1.91. This worked correctly in v2.1.87.

This is a new regression, separate from #31371 (which was about v2.1.69–2.1.70).

Steps to Reproduce

1. Install Claude Code v2.1.91
2. Open Warp terminal on macOS
3. Run claude
4. Type text, press Shift+Enter

Expected Behavior

A newline is inserted in the chat input.

Actual Behavior

The message is submitted (same as pressing Enter).

Key Observation

In the same Warp window, tabs still running v2.1.87 have working Shift+Enter, while new tabs running v2.1.91 do not. This confirms the regression is in Claude Code's input handler between these two versions, not in Warp.

Additional Details

• Adding shift+enter: chat:newline to ~/.claude/keybindings.json does not fix the issue.
• /terminal-setup reports "Shift+Enter is natively supported in Warp" but it does not work.
• Workaround: Ctrl+J still works for inserting newlines.

Environment

• macOS (Darwin 25.4.0)
• Warp terminal
• Claude Code v2.1.91 (broken), v2.1.87 (working)