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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

claude attach now measures time-to-interactive

Under the hood
Useful2 Signal0
Sessions

Attaching to a background session now times how long it takes to paint and reach an idle prompt.

claude attach
What

Attaching to a background session records how long it takes to reach first paint and an idle prompt, alongside how much of the transcript was loaded and rendered.

Details
  • A gesture record is created up front and the child's output is watched for content-paint and prompt-idle marks.
  • tengu_bg_attach_outcome gained attach_ms, content_paint_ms, prompt_idle_ms, msgs_loaded, msgs_in_jsonl, msgs_rendered_at_first_paint, first_frame_kind and marks_expected.
  • Daemon boot is marked when the daemon starts.
  • Error exits (crash loop, respawn failure, daemon unavailable) flush the gesture with a 750 ms race before exiting.
Evidence

msgs_rendered_at_first_paint

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 →