[Bug] Shift+Enter submits prompt instead of inserting newline on Windows Terminal

Bug Description
Environment:

• Windows 11 Enterprise 10.0.26300
• Windows Terminal 1.24.11911.0
• Process chain: WindowsTerminal.exe -> powershell.exe -> claude.exe
• No custom keybindings (~/.claude/keybindings.json absent, no shift+enter

action in Windows Terminal settings.json)

Expected: Shift+Enter inserts a newline in the prompt.
Actual: Shift+Enter submits the prompt, same as Enter.

/terminal-setup reports "Shift+Enter is natively supported in Windows
Terminal. No configuration needed." — but it does not work.

The terminal does deliver the Shift modifier. In a separate Windows Terminal
tab, this PowerShell loop:
while ($true) { $k = [Console]::ReadKey($true); "$($k.Key) $($k.Modifiers)" }
prints "Enter Shift" for Shift+Enter and "Enter 0" for Enter.
So the modifier is lost inside Claude Code, not by the terminal.

Workarounds that work: "\" + Enter, Ctrl+J.

Environment Info

• Platform: win32
• Terminal: windows-terminal
• Version: 2.1.289
• Feedback ID: 1a6e176b-fb84-47fb-a88f-d37844423f9d