/fork refuses in additional edge cases with clear messages:
Session not yet saved: "Couldn't fork — this conversation is still being saved. Try again in a moment."
No messages yet: "Nothing to fork yet — send a message first."
Session started with incompatible launch flags: describes which flags prevent inheritance.
Evidence
"Cannot fork — session persistence is off, so the new session would have nothing to start from." (search for "Cannot fork")
Strings lifted out of the shipped bundle, so the claim above can be checked against them.
How sure we are
One source agreesOne thing we can check says the same as this entry.
Anthropic's release notes agree/fork now copies your conversation into a new background session (its own row in claude agents) while you keep working; the in-session…
