Shift+Return no longer creates newline in input (regression in v2.1.70)

Describe the bug

Shift+Return (used for multi-line input) stopped working in v2.1.70. Pressing Shift+Return either sends the message or produces a backslash instead of inserting a newline. Works correctly on v2.1.69.

To reproduce

1. Update Claude Code to v2.1.70
2. Start a conversation
3. Press Shift+Return to try to create a new line

Expected behavior

A newline is inserted in the input, allowing multi-line messages before sending.

Confirmed regression

• v2.1.69: Shift+Return works correctly
• v2.1.70: Shift+Return broken

Environment

• Claude Code v2.1.70
• macOS (Darwin 25.3.0)
• Reproduces in both VS Code integrated terminal and Terminal.app