# Stage: prepare

## Purpose

Materialize canonical current-session inputs before processing stages.

## Inputs

- resolved campaign, session, and pipeline configuration
- stable input files (`speakers`, `autocorrect`, `glossary`, `players`, `party`)
- one resolved local or S3 audio source
- enabled configured artifact input requirements for previous-session sources

## Outputs

- `inputs/campaign.yml`
- `inputs/session.yml`
- `inputs/pipeline.resolved.yml`
- `inputs/speakers.yml`
- `inputs/autocorrect.yml`
- `inputs/glossary.yml`
- `inputs/players.yml`
- `inputs/party.yml`
- `audio/*.flac`
- optional `previous/manifest.json`
- optional `previous/artifacts/**`
- deterministic `manifest.inputs` entries (checksums + provenance)

## Key Behavior

- validates required config/store state.
- enforces local audio vs S3 audio mutual exclusivity.
- materializes S3 audio through spool/cache-aware logic.
- scans enabled configured artifact inputs for `narratio.previous_session.artifact.*` requirements.
- when previous requirements exist:
  - clears managed `previous/` state;
  - builds previous-cache remote plan;
  - downloads previous manifest/artifacts;
  - records previous inputs in `manifest.inputs`.

Required previous-session inputs fail when unavailable; optional missing inputs are skipped.

## Invariants

- only `prepare` hydrates canonical `previous/` cache state.
- managed previous artifacts are stored under `previous/artifacts/**` without
  duplicate `artifacts/artifacts/` nesting.
- `manifest.inputs` ordering is deterministic (`kind`, `path`).

## Related Contracts And Tests

- [Configuration](../config.md) owns audio selection, stable input fields, and
  previous-session settings.
- [Operations](../operations.md) owns physical input, audio, spool, cache, and
  previous-state layout.
- [Storage Internals](storage.md) and [Artifact Internals](artifacts.md) explain
  the internal collaborators.
- Implementation and tests: `internal/stage/prepare.go`,
  `internal/stage/prepare_test.go`, `internal/audio/s3_audio_test.go`,
  `internal/previouscache/*_test.go`