DisclaimerUnofficial, and not affiliated with Anthropic. Nearly all of this is read straight out of what ships: npm bundles, captured prompts, published docs. Anthropic's own notes go in verbatim, marked as theirs. The rest is my reading, and every entry carries the strings behind it. If one looks wrong, vote it down and say why.
Clear message when resuming a session that is still running
You'll notice
Useful4Signal2
Sessions
Resuming a session that is still running now offers to attach, stop or fork it.
What's wrong with this entry?
Anonymous. No account, no email.
What
Trying to resume or fork a session that is currently running as a background session now explains the situation and gives the options: attach to it, stop it, or fork a copy. Previously this surfaced as a generic error.
Details
Triggered whenever the target session is detected as an active background job. Available to everyone, no flag.
Evidence
That session is still running as a background session
Strings lifted out of the shipped bundle, so the claim above can be checked against them.