# K1 audio classification projection fold
Pure, non-interactive composition for one audio-classification fragment across V5, V6, and V7. `fold(current, callback_txid, payload)` returns the fragment, `ProjectionEffect`, and an optional complete `FragmentProjection`; `None` is a semantic no-op. `FragmentProjection` exposes identity, overlaid visible status, ordered `ResumePlan`, work eligibility, retained-completion label validation, and feature-gated bounded error injection. `FoldResult` and `ResumePlan` expose their documented fields. State, artifact signature, and effect types remain re-exported.
Decoded V5 and V6 callbacks delegate to their versioned pure fold owners. V5 retains lifecycle, execution fencing, and legacy completion repair; V6 retains attempt and artifact transitions. V7 requires a known matching fragment. Discarded, settled, and stale-attempt V7 callbacks are no-ops before nested completion validation; current Running attempts are fully validated. Accepted V7 stores final analysis, the first callback as interim identity, succeeded analysis stages, and Completed or Confirmed state. Exact later duplicates preserve that first identity. Visible status overlays durable artifacts. Resume plans expose ordered artifacts and an active attempt only for incomplete Running work; `needs_work` is true only for incomplete Queued or Running work. The crate performs no I/O, scheduling, retry, persistence, locking, provider work, or deployment.