[AZ-284] Autodev baseline + testability refactor

Phase A baseline outputs from /autodev (Steps 1-5):
- Problem & solution docs (_docs/00_problem, _docs/01_solution)
- Codebase documentation (_docs/02_document) incl. architecture,
  module-layout, glossary, system-flows, baseline compliance scan
- Test specs (blackbox, performance, resilience, security, resource,
  traceability matrix)
- Test task decomposition (_docs/02_tasks/todo): AZ-285..AZ-290
- Testability refactor (_docs/04_refactoring/01-testability-refactoring):
  - TC-01 Move DownloadedTileInfoV2 + new ExistingTileInfo to Common.DTO
  - TC-02 Replace dead ISatelliteDownloader API with real signatures
  - TC-03 GoogleMapsDownloaderV2 implements ISatelliteDownloader
  - TC-04 TileService depends on ISatelliteDownloader (mockable)
  - TC-05 DI + endpoints use ISatelliteDownloader
- Test runner scripts (scripts/run-tests.sh, run-performance-tests.sh)
- Autodev state pointer (_docs/_autodev_state.md)

Prepares the codebase for AZ-285..AZ-290 unit/integration test work.

Co-authored-by: Cursor <cursoragent@cursor.com>

_docs/02_document/components/04_region_processing/description.md

@@ -0,0 +1,71 @@
+# RegionProcessing
+
+## 1. High-Level Overview
+
+**Purpose**: Manages the lifecycle of geographic region tile requests — from API submission through a bounded queue to background processing that downloads tiles, generates CSV/summary files, and optionally stitches tiles into composite images.
+
+**Architectural Pattern**: Producer-Consumer with Background Workers
+
+**Upstream dependencies**: Common (DTOs, interfaces, configs, GeoUtils), DataAccess (RegionRepository), TileDownloader (ITileService)
+
+**Downstream consumers**: RouteManagement (creates regions for route points and geofences), WebApi (RequestRegion/GetRegionStatus endpoints)
+
+## 2. Internal Interfaces
+
+### Service: RegionService (implements IRegionService)
+See Common component for interface definition. Key implementation details:
+- `RequestRegionAsync`: creates DB record, enqueues to bounded channel
+- `ProcessRegionAsync`: 5-minute timeout, comprehensive error handling, generates CSV + summary + optional stitched image
+
+### BackgroundService: RegionProcessingService
+- `ExecuteAsync`: spawns N parallel workers (configurable via `MaxConcurrentRegions`) with staggered startup
+
+### Queue: RegionRequestQueue (implements IRegionRequestQueue)
+- Bounded `Channel<RegionRequest>` with `BoundedChannelFullMode.Wait`
+
+## 4. Data Access Patterns
+
+### Queries
+| Query | Frequency | Hot Path | Index Needed |
+|-------|-----------|----------|--------------|
+| Region GetByIdAsync | Very High (per processing) | Yes | PK |
+| Region UpdateAsync (status transitions) | High | Yes | PK |
+| Region InsertAsync | Medium | No | — |
+
+## 5. Implementation Details
+
+**State Management**: Region status tracked in database (queued → processing → completed/failed). Queue state is in-memory (Channel<T>).
+
+**Key Dependencies**:
+| Library | Version | Purpose |
+|---------|---------|---------|
+| SixLabors.ImageSharp | 3.1.11 | Tile stitching into composite JPEG |
+| System.Threading.Channels | built-in | Bounded async queue |
+
+**Error Handling**:
+- 5-minute processing timeout per region
+- Separate catch blocks for: timeout, external cancellation, rate limiting, HTTP errors, generic errors
+- All failures produce a summary file with error details and set status to "failed"
+
+## 7. Caveats & Edge Cases
+
+- Queue is in-memory: pending requests are lost on process restart (no persistence)
+- 5-minute timeout is hardcoded, not configurable
+- Stitching crosshair is drawn with a fixed 10-pixel arm length (±5 pixels)
+- Region status "queued" in code vs "pending" mentioned in some API documentation
+- `RegionProcessingService` workers have random startup delay (100–500ms) to avoid thundering herd on queue
+
+## 8. Dependency Graph
+
+**Must be implemented after**: Common, DataAccess, TileDownloader
+**Can be implemented in parallel with**: nothing at this layer
+**Blocks**: RouteManagement (uses IRegionService to create regions)
+
+## 9. Logging Strategy
+
+| Log Level | When | Example |
+|-----------|------|---------|
+| ERROR | Processing failure | `Failed to process region {RegionId}` |
+| ERROR | Rate limit exceeded | `Rate limit exceeded for region {RegionId}` |
+| WARN | Region not found, missing tile file | `Region {RegionId} not found in database` |
+| INFO | Service start/stop, queue creation | `Region Processing Service started with {N} workers` |