You'll notice
Forking a session now fails outright if the fork point can't be saved, instead of silently continuing
What
When Claude Code creates a forked or background session, it now treats writing the fork point (a marker recording where the fork branched off, along with the last prompt) as required, separate from the fork briefing text, which stays optional. If the required fork-point marker fails to write, forking now fails with an explicit error. Previously, a failed write here only logged a warning and the fork went ahead anyway.
Why
This stops a fork from silently proceeding without a properly recorded starting point, which could otherwise lead to a forked session that doesn't know exactly where it branched from.