# PR-25 Asset Cache Model and Repository

Domain Owner: `docs/packer`

## Briefing

`PR-24` defines the need for a durable asset file cache in `assets/.prometeu/cache.json`, but the first executable slice should stop at cache persistence itself.

Before walkers or runtime snapshot integration can reuse prior file facts safely, the packer needs a stable cache schema, explicit load/save ownership, and tests that prove the cache is keyed correctly and excludes non-cacheable data.

## Objective

Deliver the durable `cache.json` model and repository, keyed by stable `asset_id`, with no persisted diagnostics.

## Dependencies

- [`./PR-24-asset-file-cache-hydration-and-walker-reuse.md`](./PR-24-asset-file-cache-hydration-and-walker-reuse.md)
- [`./PR-14-project-runtime-core-snapshot-model-and-lifecycle.md`](./PR-14-project-runtime-core-snapshot-model-and-lifecycle.md)
- [`../specs/2. Workspace, Registry, and Asset Identity Specification.md`](../specs/2.%20Workspace,%20Registry,%20and%20Asset%20Identity%20Specification.md)

## Scope

- define the durable schema for `assets/.prometeu/cache.json`
- key asset cache ownership by stable `asset_id`
- omit unregistered assets from durable cache ownership entirely
- key file cache entries by normalized relative path inside the asset root
- persist reusable probe facts only:
  - `mimeType`
  - `size`
  - `lastModified`
  - fingerprint/hash
  - family-specific metadata
- exclude diagnostics from the durable cache artifact
- add a packer-owned repository for cache load/save and schema validation

## Non-Goals

- no walker contract changes yet
- no cache comparison or reuse policy yet
- no runtime snapshot model changes yet
- no Studio adapter changes

## Execution Method

1. Add cache model types under the packer runtime model layer.
2. Define one versioned workspace cache artifact for `assets/.prometeu/cache.json`.
3. Encode asset entries by `asset_id`, never by asset root path.
4. Encode file entries by normalized asset-relative path.
5. Add repository load/save behavior with safe fallback on missing or invalid cache files.
6. Prove by tests that diagnostics cannot be serialized into the durable cache artifact.

## Acceptance Criteria

- the packer has explicit model types for the durable cache artifact
- cache ownership is keyed by `asset_id`
- unregistered assets do not receive durable cache entries
- file cache entries are keyed by normalized relative file path
- repository load on absent cache returns a safe empty state
- malformed or schema-incompatible cache can be rejected cleanly without crashing the runtime load path
- diagnostics are not part of the serialized cache schema

## Validation

- schema serialization tests for workspace cache
- repository round-trip tests for valid cache content
- repository tests for absent cache file
- repository tests for malformed cache file
- cache model tests proving `asset_id`-aligned lookup
- serialization tests proving diagnostics are excluded from `cache.json`

## Affected Artifacts

- `docs/packer/pull-requests/**`
- `prometeu-packer/prometeu-packer-v1/src/main/java/p/packer/repositories/**`
- `prometeu-packer/prometeu-packer-v1/src/main/java/p/packer/models/**`
- `prometeu-packer/prometeu-packer-v1/src/test/java/p/packer/repositories/**`