Add scanner-to-api design document

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/plans/2026-05-07-scanner-to-api-design.md

@@ -0,0 +1,109 @@
+# PAD Scanner to API - Design
+
+## Goal
+
+Build a Flutter app on the D500 PAD scanner device that captures scanned barcodes and sends the data to a configurable HTTP endpoint via POST request. This is a proof-of-concept to validate the end-to-end data pipeline.
+
+## Architecture
+
+```
+D500 Scanner Hardware
+       │
+       ▼
+Device Scan Service (system broadcast)
+  action: com.android.server.scannerservice.broadcast
+  key: scannerdata
+       │
+       ▼
+Flutter App
+  BroadcastReceiver (Android native)
+       │
+       ▼
+  EventChannel → Dart stream
+       │
+       ▼
+  HTTP POST to user-configured URL
+       │
+       ▼
+User's backend (Postman / custom server)
+```
+
+## App Pages
+
+### Main Page (Scan Records)
+
+- Real-time status indicator (waiting for scan / sending / sent / failed)
+- List of scanned barcode records, each showing:
+  - Barcode content
+  - Barcode type (CODE128, QR, etc.)
+  - Timestamp
+  - Send status (pending / success / failed)
+- AppBar with settings gear icon
+
+### Settings Page
+
+- URL input field (e.g. `http://192.168.1.100:8000/scan`)
+- Save button
+- Test connection button (sends a test request)
+
+## HTTP Request Format
+
+```
+POST {user-configured-url}
+Content-Type: application/json
+
+{
+  "barcode": "scanned content",
+  "code_type": "CODE128",
+  "timestamp": "2026-05-07T10:30:00Z"
+}
+```
+
+Expected response: any 2xx status code = success.
+
+## Technical Implementation
+
+### Scanner Data Capture
+
+- Register an Android `BroadcastReceiver` in `MainActivity.kt` to listen for `com.android.server.scannerservice.broadcast`
+- Forward scanned data to Flutter via `EventChannel` as a stream
+- BroadcastReceiver registration: dynamic (in code), not static (in manifest) - register on resume, unregister on pause
+
+### HTTP Client
+
+- Dart `http` package for POST requests
+- Async fire-and-forget on each scan result
+- Store failed requests in local list for retry display
+
+### URL Persistence
+
+- `shared_preferences` package to save/load the configured endpoint URL
+- Default value: empty (user must configure before scanning)
+
+### Dependencies
+
+```yaml
+dependencies:
+  http: ^1.2.0
+  shared_preferences: ^2.2.0
+```
+
+## File Changes
+
+| File | Action |
+|------|--------|
+| `lib/main.dart` | Rewrite - app entry with routing |
+| `lib/pages/scan_page.dart` | New - main scan records page |
+| `lib/pages/settings_page.dart` | New - URL configuration page |
+| `lib/services/scanner_service.dart` | New - EventChannel wrapper for scanner |
+| `lib/services/api_service.dart` | New - HTTP POST client |
+| `lib/models/scan_record.dart` | New - scan record data model |
+| `android/app/src/main/kotlin/.../MainActivity.kt` | Modify - add BroadcastReceiver + EventChannel |
+| `pubspec.yaml` | Modify - add dependencies |
+
+## Out of Scope
+
+- FastAPI backend implementation (user handles separately)
+- Database persistence in app
+- Authentication / encryption
+- Offline queue / retry mechanism