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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

Background sessions emit "interactive-mark" frames

Under the hood
Useful3 Signal0
Sessions Notable

Background sessions now send readiness marks so attaching knows when a session is actually interactive.

What

A new frame type flows from a background or rendezvous session to the daemon, carrying interactivity marks used to decide attach readiness.

Details
  • marks are queued before the socket is up
  • deduped to at most two, one per kind, per record
  • replayed to attachers that advertise the imark capability, forwarded with the attacher's own nonce
  • included in the session snapshot
  • new marksCapable and bootingForAttachMetrics accessors derive attach-readiness from the marks, feeding "marks capable" attach metrics
  • malformed frames are dropped with a warning and counted via a new event
  • none of this exists in v2.1.220
Evidence

dropped malformed rv interactive-mark frame, tengu_bg_imark_malformed

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

See this entry in the whole of v2.1.221 →