Resuming a session that is running in the background now opens it and hands over your prompt

What

A background session is a Claude Code conversation that keeps running without a terminal window attached to it. Before, choosing one in /resume or with claude --resume stopped with a message saying the session was still running, and told you to run claude attach or claude stop. Now Claude Code tries to open it for you:

• The session is opened as if you had run claude attach <jobId>, and Claude Code prints "Opening ..., running in the background".
• If you gave a prompt, it is first sent to that session so it runs as the next turn.
• Before handing over, Claude Code checks that the background session is running the same Claude Code build. If it is not, you get an ESKEW error.
• This needs an interactive terminal for both input and output. It does not happen with conflicting flags such as an --output-format other than text.
• The path sits behind tengu_resume_open_live_bg, whose built-in fallback is on when the server sends no value.

If opening fails or a launch prompt is still pending, a screen explains why. It now shows the session title followed by " is running in the background". It also says whether your prompt was queued, not confirmed, or not sent, and still suggests claude attach, claude stop and claude --resume ... --fork-session. A separate message tells you when your latest conversation is running in the background. It points to claude agents or claude --resume, and adds --fork-session when forking into a new copy is possible.

Why

Resuming a busy background session no longer dead-ends, and a prompt you typed is not silently lost. You are told what happened to it.