# Module: Common infrastructure

## Purpose

Cross-cutting **filesystem layout** (annotation images, labels, thumbnails, results), **global error JSON**, and trivial shared API types.

## Components

### `PathResolver` (`Services/PathResolver.cs`)

- Lazy-loads paths from `directory_settings` via `AppDataConnection`.
- Methods: `GetImagePath`, `GetLabelPath`, `GetThumbnailPath`, `GetResultPath`, `GetMediaDir` — paths under configured dirs with `{annotationId}.jpg` / `.txt` patterns.
- `Reset()` clears cache after directory settings change.

### `ErrorHandlingMiddleware` (`Middleware/`)

Maps exceptions to `{ statusCode, message }` JSON (400/404/409/500). Aligns HTTP outcomes with `01_annotations.md` status tables.

### Shared DTOs (`DTOs/`)

- `PaginatedResponse<T>` — list + `totalCount` / `page` / `pageSize` (annotations list, media list, dataset).
- `ErrorResponse` — available for explicit error contracts where used.

### `GlobalUsings.cs`

Project-wide usings only.

## Dependencies

- `PathResolver` → `AppDataConnection`, `DirectorySettings` entity.

## Consumers

All services and controllers that touch disk or return paged lists.

## Suite doc

File cleanup on DELETE annotation (`GetImgPath` / label / thumb) in `01_annotations.md` §4.