New-thread send shortcut: review evidence

Review evidence for the new-thread send-shortcut fix. This prerelease contains screenshots and recordings only, not application binaries.

Before: upstream main at 67c0fc0. After: 47e1a88.

Captured with T3 Code Browser on Linux Chromium against an isolated development instance and disposable project. Native Ctrl+Enter events exercise the Linux Mod shortcut; macOS uses Command. Before, Ctrl+Enter starts new chats in the background under both modifier-required send settings. After, it opens the new chat, while Ctrl+Shift+Enter still starts in background. Screenshots and recordings are unmodified.

PR #20929 review evidence

Review evidence for pingdotgg#20929. This prerelease stores screenshots and a short interaction recording only; it is not an application release.

Captured from an isolated development instance in Chromium on Linux, using a disposable project and a live Codex run waiting on sleep. Ctrl is the Linux equivalent of Command for the Mod shortcut. Settings: Ctrl+Enter always, follow-up behavior Steer.

Before: parent commit 89b42bf queues the follow-up on Ctrl+Enter. After: 8aec848 steers on Ctrl+Enter and queues on Ctrl+Shift+Enter. The MP4 shows the after Ctrl+Enter interaction. Screenshots are unmodified browser captures.