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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.

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Claude Code v2.1.221

Forked background sessions get clearer worktree guidance

You'll notice
Useful3 Signal0
Sessions not in their notes

Forked background sessions are told to stay in their own worktree and never touch the original session's branch.

appendSystemPrompt
What

The system prompt appended to a forked session that keeps the parent alive was rewritten to be explicit about isolation.

Details
  • names the tool to use for isolation
  • tells the fork never to enter the original session's worktree and explains why not to check out the original's branch
  • adds a new "own-worktree" case for forking out of the user's own checkout
  • the line is skipped if the same text is already present in appendSystemPrompt
  • only added for forks that keep the parent session alive
Evidence

so your edits don't land where the original session is editing.

Strings lifted out of the shipped bundle, so the claim above can be checked against them.

Related

Other releases about the same thing. Found by shared names or similar wording; neither means one caused the other.

See this entry in the whole of v2.1.221 →