0.147.0: Screenshots take half the space

humanish 0.147.0 keeps a computer-use participant's screenshots as lossless WebP, 0.47 to 0.55 of
the PNG size with the same pixels, and verify, study analysis and export read them; earlier
humanish versions refuse a bundle with WebP screenshots. actor.serviceTier: fast runs OpenAI
computer-use participants in Fast mode. On the Taskly benchmark a Fast mode step took 14% less
time at 2.15 times the participant cost, and each request is priced at the tier that served it.

Added

• actor.serviceTier: fast sends every OpenAI computer-use participant request in Fast mode
  (service_tier: "fast"). The spend estimate and caps price each request at the tier the response
  says served it, from the Fast mode rates now in the rate table for gpt-5.6-sol, gpt-6.1-sol,
  gpt-6-luna and gpt-6-astra. The trace records the requested tier in modelSettings.serviceTier
  and the served tier on each tokenUsage.turns record. A study that asks for Fast mode on a model
  without a Fast mode rate, or on a route that does not send it, is refused before it starts. The
  benchmark takes --participant, --service-tier and --persona.

Changed

• A computer-use participant's screenshots end as lossless WebP, about half the bytes of PNG: 0.47
  to 0.55 of the PNG size on 511 retained frames, with the same pixels. Each frame is written as
  PNG during the session, as the live Observer reads it, and encoded in one worker thread off the
  turn's path. When the participant ends, its trace names the WebP of each frame encoded by then,
  and the run removes those PNGs once its final bundle is written. A frame still encoding after
  5 s, or past the worker's 64 MB queue, stays PNG, and so does every frame of a study with
  policies.redactScreenshots: true. An interrupted run keeps both files of a frame.
• verify, study analysis and export --format bundle accept lossless WebP screenshots at
  screenshots/**/*.webp beside PNG ones. Verify reads a WebP frame's structure: a RIFF file
  holding one lossless VP8L chunk, with no Exif, XMP or ICC data, under the PNG pixel cap. A WebP
  frame is always full-fidelity evidence, so only a blurred PNG counts as blurred. Analysis sends a
  WebP capture as image/webp. Export blurs a WebP frame to a PNG at the same path ending .png
  and points the copy's references at it. Earlier humanish versions refuse WebP screenshots.