The pipeline was only writer->judge, missing the format quality-check
gemma does on its own output before scoring (is_usable() in revise.rs).
Added spike/agents/critic.yaml with the [critic] prompts from
prompts.toml, wired as a middle pipeline stage. Confirmed the full
three-stage pipeline runs end to end. Note in NOTES.md that the stage
runs but doesn't gate/retry -- pipeline: is linear, real retry-on-unusable
behavior would need states:/transitions:.
