Implemented shared S3 audio caching for prepare and restore --include-audio

docs/internal/command-restore.md

@@ -34,6 +34,8 @@ Does not own:
 - `pipeline.workspace.root` (local restore target root).
 - `pipeline.storage.*` (remote backend + archive identity derivation).
 - `pipeline.storage.s3.*` identity components used by archive prefix helpers.
+- `pipeline.spool.root` for active audio downloads.
+- `pipeline.cache.root` and `pipeline.cache.s3_audio` for reusable S3 audio cache.
 - `session.session_id`
 - `session.campaign`
 
@@ -48,6 +50,7 @@ Does not own:
   - `current/run_id.txt` must exist and be non-empty.
   - `current/manifest.json` must decode and match requested session/campaign.
 - Non-dry-run writes restore files to canonical session paths.
+- With `--include-audio`, restore uses the shared S3 audio cache for `audio/**` objects. Cache hits avoid object downloads; cache misses download through spool, install the work file, and populate cache.
 - Manifest install behavior:
   - validated before replacement.
   - installed last among download actions.
@@ -72,6 +75,7 @@ Restore path scope:
 ## Skip and resume behavior
 - Restore does not participate in stage skip/resume decisions.
 - Restore provides durable local state so subsequent stage commands can resume or rerun based on restored manifest state.
+- Audio cache is outside the workspace and is reused across restore and prepare invocations.
 - Dry-run is read-only and returns plan output only.
 
 ## Failure behavior