# Internal: Command Restore

## Purpose
Define the implemented `narratio session restore` contract: committed remote-state discovery, deterministic plan classification, safe file install semantics, and restore reporting.

## Inputs and outputs
Inputs:
- CLI syntax: `narratio session restore <session_id>`.
- CLI flags: `--config`, `--campaign`, `--campaign-file`, `--session`, `--previous-session-id`, `--dry-run`, `--force`, `--include-audio`.
- Resolved/validated `pipeline.yml` and `session.yml`.
- Configured remote object store.
- Remote committed current-state markers (`current/run_id.txt`, `current/manifest.json`).

Outputs:
- Dry-run summary to stdout (plan + counts).
- Non-dry-run completion summary to stdout.
- Local durable session files restored under canonical session root.
- Non-dry-run restore report at `reports/restore-latest.json`.

## Boundaries
Owns:
- Restore command flag parsing and command wiring.
- Remote current-state discovery and identity validation.
- Restore plan construction and conflict classification.
- Restore execution for planned downloads.
- Restore report model and persistence.

Does not own:
- Stage execution orchestration (`run`, `resume`, `run-stage`).
- Publish-stage behavior.
- Storage transport implementation details (owned by storage adapters).

## Config fields used
- Config/session discovery and templating fields consumed by all commands.
- `pipeline.workspace.root` (local restore target root).
- `pipeline.storage.*` (remote backend + publish identity derivation).
- `pipeline.storage.s3.*` identity components used by session-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`

## External adapters used
- `storage.ObjectStore` for `Exists`, `List`, `Download`.
- `artifacts.Store` (`LocalStore`) for layout and session lock management.
- `manifest.LocalStore` for manifest decode/validation and identity checks.

## State and manifest behavior
- Restore is not a pipeline run and does not create a run manifest.
- Restore uses committed remote current state only:
  - `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.
  - existing local manifest is preserved if restored manifest validation/install fails.
- Non-dry-run report persists summary/action status metadata in `reports/restore-latest.json`.

Restore path scope:
- includes:
  - `manifest.json`
  - `transcripts/**`
  - `artifacts/**`
  - `previous/**`
  - `audio/**` only when `--include-audio` is set
- excludes:
  - `runs/**`
  - `logs/**`
  - `reports/**`
  - `config/**`
  - `inputs/**`
  - remote `current/**` pointer files as local restore targets

## 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
- Fails when storage backend is unavailable or publish identity cannot be resolved.
- Fails when remote current pointer/manifest is missing or invalid.
- Fails when remote manifest identity mismatches requested campaign/session.
- Fails on local conflicts unless `--force` is set.
- Fails fast on session lock acquisition conflict for non-dry-run execution.
- On execution failure, previously installed files remain; no rollback is performed.

## Tests to inspect before changing
- `internal/app/restore_test.go`
- `internal/app/restore_discovery_test.go`
- `internal/app/restore_plan_test.go`
- `internal/app/restore_execution_test.go`
- `internal/app/restore_workflow_test.go`
- `internal/artifacts/archive_identity_test.go`

## Architectural invariants
- Restore relies on centralized path/key helpers (`internal/artifacts`) rather than ad hoc key building.
- `current/run_id.txt` is the remote commit marker; restore must not infer committed state from incidental files.
- Local path mapping is traversal-safe and constrained to session root.
- Restore scope is deterministic and path-classified:
  - include `manifest.json`, `transcripts/**`, `artifacts/**`, `previous/**`
  - include `audio/**` only with `--include-audio`
  - exclude `runs/**`, `logs/**`, `reports/**`, `config/**`, `inputs/**`
- Command remains standalone; no implicit `run --restore` behavior.