# Tile Caching (Filesystem)

## Module
Attestor

## Status
IMPLEMENTED

## Description
Filesystem-based immutable tile cache for Rekor v2 tiles, SHA-256 indexed, suitable for offline/air-gap scenarios.

## Implementation Details
- **Filesystem Rekor Tile Cache**: `src/Attestor/StellaOps.Attestor/StellaOps.Attestor.Core/Rekor/FileSystemRekorTileCache.cs` -- filesystem-based tile cache implementing `IRekorTileCache.cs`. Stores tiles by SHA-256 content hash for deduplication and immutability.
- **Tile Cache Interface**: `Rekor/IRekorTileCache.cs` -- abstraction for tile caching (get, put, exists operations).
- **Content-Addressed Tile Store**: `StellaOps.Attestor.TileProxy/Services/ContentAddressedTileStore.cs` -- content-addressed storage for tiles with SHA-256 indexing.
- **Tile Proxy Service**: `StellaOps.Attestor.TileProxy/Services/TileProxyService.cs` -- serves cached tiles for offline verification.
- **Tile Sync Job**: `StellaOps.Attestor.TileProxy/Jobs/TileSyncJob.cs` -- background job syncing tiles from remote Rekor while online.
- **Tile Endpoints**: `StellaOps.Attestor.TileProxy/Endpoints/TileEndpoints.cs` -- HTTP endpoints for serving cached tiles.
- **Tile Proxy Options**: `StellaOps.Attestor.TileProxy/TileProxyOptions.cs` -- configuration options (cache directory, sync interval, max tile size).
- **Tests**: `__Tests/StellaOps.Attestor.Core.Tests/TileCacheTests.cs`

## E2E Test Plan
- [ ] Store a tile via `FileSystemRekorTileCache` and verify it is retrievable by SHA-256 hash
- [ ] Store the same tile twice and verify deduplication (only one copy on disk)
- [ ] Verify immutability: attempt to overwrite a cached tile and verify the operation is rejected or idempotent
- [ ] Sync tiles from a remote Rekor via `TileSyncJob` and verify they are cached locally
- [ ] Serve a cached tile via `TileEndpoints` and verify the response matches the original tile
- [ ] Verify offline scenario: disable network, request a tile via `TileProxyService`, and verify the cached tile is served
- [ ] Verify content-addressed storage: store tiles of different sizes and verify SHA-256 indexing works correctly