[FEATURE] Handle Shift+Enter as a unique key sequence instead of just passing literal newline

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

This is a reopening of closed / locked Issue 14939

I would like to bind Shift+Enter such as for CLI tools where I would like to enter multi-line text (e.g. CoPilot CLI, but probably also Claude, Cursor, etc. all might have the same issue).

If I enter command in my shell cat -v, then I press Shift+Enter, it just shows a new line and nothing special I can bind.

Proposed Solution

Handle Shift+Enter differently than Enter to allow keybind (like ^[[1;2R or ^[[13;2u).

Alternative Solutions

_No response_

Priority

High - Significant impact on productivity

Feature Category

Interactive mode (TUI)

Use Case Example

Example scenario:

1. I'm using a TUI application.
2. Enter (newline) is configured to submit a prompt.
3. But I actually want to add another line in the same prompt before submitting.
4. Shift+Enter should be able to allow multi-line text.

Additional Context

_No response_