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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 v2.1.239

Session-to-session messages refuse to send to a record impersonating the current session

You'll notice
Useful2 Signal3
Session Messaging

Messages to another Claude session are refused if a local record impersonates your own session.

What

When sending a message to another Claude session, Claude Code now checks whether a session record on the machine claims the same identifying token this session advertises for itself. If so, the send is refused and the model is told the record is suspicious and to ask you.

Details
  • Applies unconditionally on that send path.
  • The refusal text shown to the model is "A record impersonating this session is suspicious: ask the user."
Evidence

A record impersonating this session is suspicious: ask the user.

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 v2.1.239 →