Shift+Enter still does not insert newline in chat input (regression from #751) #878

Description:
In Vibe CLI v2.18.4, pressing Shift+Enter in the chat input still submits the message instead of inserting a new line, despite issue #751 being marked as completed.

Steps to reproduce:

1. Launch Vibe CLI v2.18.4
2. Type some text in the chat input
3. Press Shift+Enter
4. Observe: message is submitted (same as pressing Enter)
5. Note: Ctrl+J works correctly and inserts a newline

Root cause analysis:
In vibe/cli/textual_ui/widgets/chat_input/text_area.py:

• Line 37: Binding "shift+enter,ctrl+j" → insert_newline is correctly defined
• Line 157-158: action_insert_newline() correctly inserts \n
• Line 336-339: Event handler intercepts shift+enter and stops it WITHOUT calling the action:

  if event.key == "shift+enter":
      event.prevent_default()
      event.stop()
      return

This handler runs before the binding can trigger, effectively blocking Shift+Enter. Ctrl+J works because it is not intercepted by this handler.

Expected behavior:
Shift+Enter should insert a newline in the chat input, just like Ctrl+J does.

Actual behavior:
Shift+Enter submits the message (same as Enter).

Version:

• Vibe CLI: 2.18.4
• OS: macOS (reporter confirmed it works everywhere else)

Related:

• Issue Shift+Enter submits instead of creating new line in chat input #751 was closed as "completed" on 2026-06-07, but the bug persists
• Issue Can we have multi-line input please? #193 also mentioned this problem

Suggested fix:
Either:

1. Remove lines 336-339 entirely (let the binding handle it), OR
2. Replace the handler with: self.action_insert_newline()