# Internal: Command Restore

## Purpose

Explain the implemented restore discovery, planning, installation, and
reporting flow in `internal/app`. User invocation belongs in
[CLI](../cli.md#session-restore), and the operator recovery procedure and
physical restore scope belong in
[Operations](../operations.md#restore-workflow).

Restore is split into explicit phases so remote authority, local conflict
policy, and filesystem mutation can be tested independently.

## Discovery Contract

Discovery delegates current-state pointer and manifest loading to
`internal/artifacts`, then validates the result against the resolved request:

- campaign must match;
- session ID must match.

Restore treats any missing or invalid remote current state as a command error.

## Planning Contract

Restore planner action kinds:

- `download`;
- `skip_same`;
- `conflict`.

Planner behavior:

- remote list scope is the resolved session prefix;
- remote-to-local mapping is traversal-safe;
- actions are sorted by local relative path and then remote key;
- force converts differing local targets from conflicts to downloads.

Previous-cache files are planned separately through `previouscache.BuildPlan`
when configured previous-session requirements exist.

## Execution Contract

Execution order and safety:

- non-manifest downloads happen before manifest install;
- `manifest.json` installs last;
- downloads use sibling temp files plus atomic rename;
- manifest replacement is validated before rename;
- failed installs do not roll back files already written in the same execution.

Audio restore path:

- uses `audio.MaterializeS3Audio`;
- integrates spool and S3 audio cache paths;
- supports cache-hit reuse without object redownload.

## Reporting Contract

- dry-run mode prints a summary and performs no local writes;
- execution mode persists the canonical restore report described in
  [Operations](../operations.md#restore-workflow);
- report includes plan counts, per-action status, and execution failures.

## Invariants

- restore uses committed remote current state as authority;
- `current/run_id.txt` is the remote publish commit marker;
- restore does not execute pipeline stages.

## Implementation And Tests

- Discovery: `internal/app/restore_discovery.go`
- Planning: `internal/app/restore_plan.go`, `internal/previouscache`
- Execution: `internal/app/restore_execute.go`
- Reporting and command coordination: `internal/app/restore_report.go`,
  `internal/app/restore.go`
- Tests: `internal/app/restore_discovery_test.go`,
  `internal/app/restore_plan_test.go`,
  `internal/app/restore_execution_test.go`,
  `internal/app/restore_workflow_test.go`