feat(android-terminal): Phase B — setup screen with QR scanner

End-to-end pairing flow:

1. SetupScreen renders a CameraX preview on the left, a manual-entry
   form on the right (dev fallback). Camera permission is requested
   in-place — no accompanist dep.
2. QrScannerView uses ML Kit's barcode scanner (QR format only),
   single-shot fires the decoded JSON to the ViewModel and stops
   analysing.
3. SetupViewModel.pairFromQr decodes via Moshi, persists the pairing
   in DataStore, then verifies by hitting /api/v1/store/loyalty/program
   through the AuthInterceptor (which now sees the new url + token).
   On 200 it warms the staff PIN and category caches and emits Success;
   on failure it rolls back via DeviceConfigRepository.resetDevice() so
   the user is back at a clean Setup with an error.
4. The NavHost watches is_device_set_up and forwards to PIN once Success
   fires. The DataStore key was aligned to "is_device_set_up" so this
   reactive switch keeps working.

Backend: the QR payload generated by POST /merchants/loyalty/devices
now includes store_id and store_name in addition to api_url, store_code
and auth_token, so the tablet doesn't have to resolve them later via a
separate call. Old QRs (which only had three fields) won't decode — the
merchant has to revoke and re-pair, which is the same flow they'd run
anyway after losing a tablet.

Files:
- ui/scanner/QrScannerView.kt    (new) — CameraX + ML Kit composable
- ui/setup/SetupViewModel.kt     (rewrite) — pair flow + state machine
- ui/setup/SetupScreen.kt        (rewrite) — two-pane layout, status overlay
- data/model/ApiModels.kt        — SetupPayload model
- data/repository/DeviceConfigRepository.kt — IS_SET_UP key alignment
- app/modules/loyalty/services/terminal_device_service.py — richer QR payload

Verified by ./gradlew assembleDebug — clean build, all warnings address
in this commit (LocalLifecycleOwner moved to lifecycle.compose, OptIn on
ExperimentalGetImage removed since it's no longer @RequiresOptIn).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/modules/loyalty/services/terminal_device_service.py

@@ -144,7 +144,9 @@ class TerminalDeviceService:
 
         payload = {
             "api_url": settings.app_base_url,
+            "store_id": store.id,
             "store_code": store.store_code,
+            "store_name": store.name,
             "auth_token": token,
         }
         qr_png_base64 = self._render_qr_png_base64(json.dumps(payload))

clients/terminal-android/app/src/main/java/lu/rewardflow/terminal/data/model/ApiModels.kt

@@ -190,6 +190,24 @@ data class PinItem(
     val is_locked: Boolean,
 )
 
+// ── Pairing ─────────────────────────────────────────────────────────────
+
+/**
+ * JSON payload encoded in the pairing QR generated by
+ * ``POST /api/v1/merchants/loyalty/devices`` on the backend.
+ *
+ * The tablet decodes this once at the setup screen, persists the three
+ * fields via DeviceConfigRepository, and then never sees the QR again.
+ */
+@JsonClass(generateAdapter = true)
+data class SetupPayload(
+    val api_url: String,
+    val store_id: Int,
+    val store_code: String,
+    val store_name: String? = null,
+    val auth_token: String,
+)
+
 // ── Categories ──────────────────────────────────────────────────────────
 
 @JsonClass(generateAdapter = true)

clients/terminal-android/app/src/main/java/lu/rewardflow/terminal/data/repository/DeviceConfigRepository.kt

@@ -104,7 +104,9 @@ class DeviceConfigRepository @Inject constructor(
         private val KEY_STORE_ID = intPreferencesKey("store_id")
         private val KEY_STORE_CODE = stringPreferencesKey("store_code")
         private val KEY_STORE_NAME = stringPreferencesKey("store_name")
-        private val KEY_IS_SET_UP = booleanPreferencesKey("IS_SET_UP")
+        // Matches the key the existing SetupViewModel observed; keep this
+        // exact string so the NavHost's start-destination switch works.
+        private val KEY_IS_SET_UP = booleanPreferencesKey("is_device_set_up")
         private val KEY_PROGRAM_JSON = stringPreferencesKey("program_json")
         private val KEY_STAFF_PINS_JSON = stringPreferencesKey("staff_pins_json")
         private val KEY_CATEGORIES_JSON = stringPreferencesKey("categories_json")

clients/terminal-android/app/src/main/java/lu/rewardflow/terminal/ui/scanner/QrScannerView.kt

@@ -0,0 +1,184 @@
+package lu.rewardflow.terminal.ui.scanner
+
+import android.Manifest
+import android.content.pm.PackageManager
+import android.util.Log
+import androidx.activity.compose.rememberLauncherForActivityResult
+import androidx.activity.result.contract.ActivityResultContracts
+import androidx.camera.core.CameraSelector
+import androidx.camera.core.ImageAnalysis
+import androidx.camera.core.Preview
+import androidx.camera.lifecycle.ProcessCameraProvider
+import androidx.camera.view.PreviewView
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.padding
+import androidx.compose.material3.Button
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.DisposableEffect
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.platform.LocalContext
+import androidx.compose.ui.res.stringResource
+import androidx.compose.ui.unit.dp
+import androidx.compose.ui.viewinterop.AndroidView
+import androidx.core.content.ContextCompat
+import androidx.lifecycle.compose.LocalLifecycleOwner
+import com.google.mlkit.vision.barcode.BarcodeScanner
+import com.google.mlkit.vision.barcode.BarcodeScannerOptions
+import com.google.mlkit.vision.barcode.BarcodeScanning
+import com.google.mlkit.vision.barcode.common.Barcode
+import com.google.mlkit.vision.common.InputImage
+import lu.rewardflow.terminal.R
+import java.util.concurrent.Executors
+import java.util.concurrent.atomic.AtomicBoolean
+
+/**
+ * CameraX preview that scans QR codes via ML Kit.
+ *
+ * Calls [onQrScanned] exactly once with the decoded raw value, then stops
+ * analysing. Re-mount the composable (or have the caller key it on a state)
+ * to scan again.
+ *
+ * Camera permission is requested in-place — when the user has not granted
+ * it, the preview area is replaced by a permission prompt. Manifest already
+ * declares `android.permission.CAMERA` as optional.
+ */
+@Composable
+fun QrScannerView(
+    modifier: Modifier = Modifier,
+    onQrScanned: (String) -> Unit,
+) {
+    val context = LocalContext.current
+
+    var hasCameraPermission by remember {
+        mutableStateOf(
+            ContextCompat.checkSelfPermission(
+                context, Manifest.permission.CAMERA
+            ) == PackageManager.PERMISSION_GRANTED
+        )
+    }
+
+    val permissionLauncher = rememberLauncherForActivityResult(
+        contract = ActivityResultContracts.RequestPermission(),
+    ) { granted ->
+        hasCameraPermission = granted
+    }
+
+    Box(modifier = modifier.fillMaxSize()) {
+        if (hasCameraPermission) {
+            CameraXPreview(onQrScanned = onQrScanned)
+        } else {
+            Column(
+                modifier = Modifier
+                    .fillMaxSize()
+                    .padding(24.dp),
+                verticalArrangement = androidx.compose.foundation.layout.Arrangement.Center,
+                horizontalAlignment = Alignment.CenterHorizontally,
+            ) {
+                Text(
+                    text = stringResource(R.string.setup_camera_permission_required),
+                    style = MaterialTheme.typography.bodyLarge,
+                )
+                Button(
+                    modifier = Modifier.padding(top = 16.dp),
+                    onClick = { permissionLauncher.launch(Manifest.permission.CAMERA) },
+                ) {
+                    Text(text = stringResource(R.string.setup_connect))
+                }
+            }
+        }
+    }
+
+    // Trigger the permission prompt the first time the composable is shown.
+    DisposableEffect(Unit) {
+        if (!hasCameraPermission) {
+            permissionLauncher.launch(Manifest.permission.CAMERA)
+        }
+        onDispose { }
+    }
+}
+
+@Composable
+private fun CameraXPreview(
+    onQrScanned: (String) -> Unit,
+) {
+    val context = LocalContext.current
+    val lifecycleOwner = LocalLifecycleOwner.current
+    val executor = remember { Executors.newSingleThreadExecutor() }
+    val alreadyScanned = remember { AtomicBoolean(false) }
+
+    val barcodeScanner: BarcodeScanner = remember {
+        BarcodeScanning.getClient(
+            BarcodeScannerOptions.Builder()
+                .setBarcodeFormats(Barcode.FORMAT_QR_CODE)
+                .build()
+        )
+    }
+
+    AndroidView(
+        modifier = Modifier.fillMaxSize(),
+        factory = { ctx ->
+            val previewView = PreviewView(ctx)
+            val cameraProviderFuture = ProcessCameraProvider.getInstance(ctx)
+
+            cameraProviderFuture.addListener({
+                val cameraProvider = cameraProviderFuture.get()
+
+                val preview = Preview.Builder().build().also {
+                    it.setSurfaceProvider(previewView.surfaceProvider)
+                }
+
+                val analysis = ImageAnalysis.Builder()
+                    .setBackpressureStrategy(ImageAnalysis.STRATEGY_KEEP_ONLY_LATEST)
+                    .build()
+                analysis.setAnalyzer(executor) { imageProxy ->
+                    val mediaImage = imageProxy.image
+                    if (mediaImage == null || alreadyScanned.get()) {
+                        imageProxy.close()
+                        return@setAnalyzer
+                    }
+                    val image = InputImage.fromMediaImage(
+                        mediaImage,
+                        imageProxy.imageInfo.rotationDegrees,
+                    )
+                    barcodeScanner.process(image)
+                        .addOnSuccessListener { barcodes ->
+                            val raw = barcodes.firstOrNull()?.rawValue
+                            if (!raw.isNullOrBlank() && alreadyScanned.compareAndSet(false, true)) {
+                                onQrScanned(raw)
+                            }
+                        }
+                        .addOnFailureListener { e ->
+                            Log.w("QrScannerView", "Barcode scan failed", e)
+                        }
+                        .addOnCompleteListener { imageProxy.close() }
+                }
+
+                cameraProvider.unbindAll()
+                cameraProvider.bindToLifecycle(
+                    lifecycleOwner,
+                    CameraSelector.DEFAULT_BACK_CAMERA,
+                    preview,
+                    analysis,
+                )
+            }, ContextCompat.getMainExecutor(ctx))
+
+            previewView
+        },
+    )
+
+    DisposableEffect(Unit) {
+        onDispose {
+            executor.shutdown()
+            barcodeScanner.close()
+        }
+    }
+}

clients/terminal-android/app/src/main/java/lu/rewardflow/terminal/ui/setup/SetupScreen.kt

@@ -1,49 +1,237 @@
 package lu.rewardflow.terminal.ui.setup
 
-import androidx.compose.foundation.layout.*
-import androidx.compose.material3.*
+import androidx.compose.foundation.background
+import androidx.compose.foundation.layout.Arrangement
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.PaddingValues
+import androidx.compose.foundation.layout.Row
+import androidx.compose.foundation.layout.Spacer
+import androidx.compose.foundation.layout.fillMaxHeight
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.height
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.shape.RoundedCornerShape
+import androidx.compose.material3.Button
+import androidx.compose.material3.CircularProgressIndicator
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.OutlinedTextField
+import androidx.compose.material3.Text
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.LaunchedEffect
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.saveable.rememberSaveable
+import androidx.compose.runtime.setValue
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
+import androidx.compose.ui.draw.clip
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.res.stringResource
+import androidx.compose.ui.text.input.KeyboardType
+import androidx.compose.ui.text.input.PasswordVisualTransformation
 import androidx.compose.ui.text.style.TextAlign
 import androidx.compose.ui.unit.dp
+import androidx.hilt.navigation.compose.hiltViewModel
+import androidx.lifecycle.compose.collectAsStateWithLifecycle
+import lu.rewardflow.terminal.R
+import lu.rewardflow.terminal.ui.scanner.QrScannerView
 
 /**
- * First-time device setup screen.
+ * First-time pairing screen.
  *
- * Flow:
- * 1. Show "Scan QR Code" prompt
- * 2. Merchant owner scans QR from web settings page
- * 3. QR contains: API URL + store auth token + store_id + store_code
- * 4. App downloads store config and enters kiosk mode
+ * Left half: live QR scanner. Decoded value is fed to [SetupViewModel.pairFromQr]
+ * which verifies with the server and persists the configuration.
+ *
+ * Right half: manual entry form (dev fallback). Same downstream flow.
+ *
+ * On successful pair, [onSetupComplete] is invoked once — the NavHost reacts
+ * to the persisted ``is_device_set_up`` flag and forwards to the PIN screen.
  */
 @Composable
 fun SetupScreen(
     onSetupComplete: () -> Unit,
+    viewModel: SetupViewModel = hiltViewModel(),
 ) {
-    Box(
-        modifier = Modifier.fillMaxSize(),
-        contentAlignment = Alignment.Center,
-    ) {
-        Column(
-            horizontalAlignment = Alignment.CenterHorizontally,
-            modifier = Modifier.padding(48.dp),
+    val state by viewModel.state.collectAsStateWithLifecycle()
+
+    LaunchedEffect(state) {
+        if (state is SetupState.Success) onSetupComplete()
+    }
+
+    Row(modifier = Modifier.fillMaxSize()) {
+        // ── Left half: QR scanner
+        Box(
+            modifier = Modifier
+                .weight(1f)
+                .fillMaxHeight()
+                .background(Color.Black),
         ) {
-            Text(
-                text = "RewardFlow Terminal",
-                style = MaterialTheme.typography.headlineLarge,
+            QrScannerView(
+                onQrScanned = { raw -> viewModel.pairFromQr(raw) },
             )
-            Spacer(modifier = Modifier.height(16.dp))
-            Text(
-                text = "Scan the setup QR code from your store settings page to configure this device.",
-                style = MaterialTheme.typography.bodyLarge,
-                textAlign = TextAlign.Center,
-            )
-            Spacer(modifier = Modifier.height(32.dp))
-            // TODO: CameraX QR scanner for setup code
-            Button(onClick = onSetupComplete) {
-                Text("Setup Complete (placeholder)")
+
+            // Status overlay on top of the camera preview
+            StatusOverlay(state = state, onDismissError = viewModel::resetError)
+        }
+
+        // ── Right half: manual entry + instruction
+        ManualEntryPanel(
+            modifier = Modifier
+                .weight(1f)
+                .fillMaxHeight()
+                .padding(32.dp),
+            isConnecting = state is SetupState.Connecting,
+            onConnect = { apiUrl, storeId, storeCode, token ->
+                viewModel.pairManually(apiUrl, storeId, storeCode, token)
+            },
+        )
+    }
+}
+
+@Composable
+private fun StatusOverlay(
+    state: SetupState,
+    onDismissError: () -> Unit,
+) {
+    when (state) {
+        is SetupState.Connecting -> {
+            Box(
+                modifier = Modifier
+                    .fillMaxSize()
+                    .background(Color.Black.copy(alpha = 0.55f)),
+                contentAlignment = Alignment.Center,
+            ) {
+                Column(horizontalAlignment = Alignment.CenterHorizontally) {
+                    CircularProgressIndicator(color = Color.White)
+                    Spacer(Modifier.height(12.dp))
+                    Text(
+                        text = stringResource(R.string.setup_connecting),
+                        color = Color.White,
+                        style = MaterialTheme.typography.bodyLarge,
+                    )
+                }
             }
         }
+
+        is SetupState.Error -> {
+            val message = when (val e = state.reason) {
+                SetupError.InvalidQr -> stringResource(R.string.setup_invalid_qr)
+                is SetupError.ConnectionFailed ->
+                    e.detail ?: stringResource(R.string.setup_connection_failed)
+            }
+            Box(
+                modifier = Modifier
+                    .fillMaxSize()
+                    .padding(24.dp),
+                contentAlignment = Alignment.BottomCenter,
+            ) {
+                Column(
+                    horizontalAlignment = Alignment.CenterHorizontally,
+                    modifier = Modifier
+                        .clip(RoundedCornerShape(8.dp))
+                        .background(MaterialTheme.colorScheme.errorContainer)
+                        .padding(16.dp),
+                ) {
+                    Text(
+                        text = message,
+                        color = MaterialTheme.colorScheme.onErrorContainer,
+                        textAlign = TextAlign.Center,
+                    )
+                    Spacer(Modifier.height(8.dp))
+                    Button(onClick = onDismissError) {
+                        Text(stringResource(R.string.error_try_again))
+                    }
+                }
+            }
+        }
+
+        else -> Unit
+    }
+}
+
+@Composable
+private fun ManualEntryPanel(
+    modifier: Modifier = Modifier,
+    isConnecting: Boolean,
+    onConnect: (apiUrl: String, storeId: Int, storeCode: String, authToken: String) -> Unit,
+) {
+    var apiUrl by rememberSaveable { mutableStateOf("") }
+    var storeIdText by rememberSaveable { mutableStateOf("") }
+    var storeCode by rememberSaveable { mutableStateOf("") }
+    var authToken by rememberSaveable { mutableStateOf("") }
+
+    Column(
+        modifier = modifier,
+        verticalArrangement = Arrangement.Center,
+    ) {
+        Text(
+            text = stringResource(R.string.setup_title),
+            style = MaterialTheme.typography.headlineMedium,
+        )
+        Spacer(Modifier.height(8.dp))
+        Text(
+            text = stringResource(R.string.setup_instruction),
+            style = MaterialTheme.typography.bodyMedium,
+            color = MaterialTheme.colorScheme.onSurfaceVariant,
+        )
+        Spacer(Modifier.height(24.dp))
+        Text(
+            text = stringResource(R.string.setup_or_manual),
+            style = MaterialTheme.typography.labelLarge,
+        )
+        Spacer(Modifier.height(8.dp))
+
+        OutlinedTextField(
+            value = apiUrl,
+            onValueChange = { apiUrl = it },
+            label = { Text(stringResource(R.string.setup_api_url)) },
+            singleLine = true,
+            placeholder = { Text("http://10.0.2.2:8000") },
+            modifier = Modifier.fillMaxWidth(),
+        )
+        Spacer(Modifier.height(8.dp))
+        OutlinedTextField(
+            value = storeCode,
+            onValueChange = { storeCode = it },
+            label = { Text(stringResource(R.string.setup_store_code)) },
+            singleLine = true,
+            modifier = Modifier.fillMaxWidth(),
+        )
+        Spacer(Modifier.height(8.dp))
+        OutlinedTextField(
+            value = storeIdText,
+            onValueChange = { storeIdText = it.filter(Char::isDigit) },
+            label = { Text("Store ID") },
+            singleLine = true,
+            modifier = Modifier.fillMaxWidth(),
+        )
+        Spacer(Modifier.height(8.dp))
+        OutlinedTextField(
+            value = authToken,
+            onValueChange = { authToken = it },
+            label = { Text(stringResource(R.string.setup_auth_token)) },
+            singleLine = true,
+            visualTransformation = PasswordVisualTransformation(),
+            modifier = Modifier.fillMaxWidth(),
+        )
+        Spacer(Modifier.height(16.dp))
+        Button(
+            enabled = !isConnecting,
+            onClick = {
+                onConnect(
+                    apiUrl.trim(),
+                    storeIdText.toIntOrNull() ?: 0,
+                    storeCode.trim(),
+                    authToken.trim(),
+                )
+            },
+            modifier = Modifier.fillMaxWidth(),
+            contentPadding = PaddingValues(vertical = 12.dp),
+        ) {
+            Text(stringResource(R.string.setup_connect))
+        }
     }
 }

clients/terminal-android/app/src/main/java/lu/rewardflow/terminal/ui/setup/SetupViewModel.kt

@@ -1,24 +1,131 @@
 package lu.rewardflow.terminal.ui.setup
 
-import androidx.datastore.core.DataStore
-import androidx.datastore.preferences.core.Preferences
-import androidx.datastore.preferences.core.booleanPreferencesKey
 import androidx.lifecycle.ViewModel
+import androidx.lifecycle.viewModelScope
+import com.squareup.moshi.JsonAdapter
+import com.squareup.moshi.JsonDataException
+import com.squareup.moshi.Moshi
 import dagger.hilt.android.lifecycle.HiltViewModel
 import kotlinx.coroutines.flow.Flow
-import kotlinx.coroutines.flow.map
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.StateFlow
+import kotlinx.coroutines.flow.asStateFlow
+import kotlinx.coroutines.launch
+import lu.rewardflow.terminal.data.api.LoyaltyApi
+import lu.rewardflow.terminal.data.model.ProgramResponse
+import lu.rewardflow.terminal.data.model.SetupPayload
+import lu.rewardflow.terminal.data.repository.CategoryRepository
+import lu.rewardflow.terminal.data.repository.DeviceConfigRepository
+import lu.rewardflow.terminal.data.repository.StaffPinRepository
 import javax.inject.Inject
 
 @HiltViewModel
 class SetupViewModel @Inject constructor(
-    private val dataStore: DataStore<Preferences>,
+    private val configRepository: DeviceConfigRepository,
+    private val api: LoyaltyApi,
+    private val staffPinRepository: StaffPinRepository,
+    private val categoryRepository: CategoryRepository,
+    moshi: Moshi,
 ) : ViewModel() {
 
-    companion object {
-        val IS_SET_UP = booleanPreferencesKey("is_device_set_up")
+    /** Observed by [RewardFlowNavHost] to pick the start destination. */
+    val isDeviceSetUp: Flow<Boolean> = configRepository.isDeviceSetUp
+
+    private val _state = MutableStateFlow<SetupState>(SetupState.Idle)
+    val state: StateFlow<SetupState> = _state.asStateFlow()
+
+    private val payloadAdapter: JsonAdapter<SetupPayload> =
+        moshi.adapter(SetupPayload::class.java)
+
+    private val programAdapter: JsonAdapter<ProgramResponse> =
+        moshi.adapter(ProgramResponse::class.java)
+
+    /** Decode the JSON encoded in the pairing QR and run the pair flow. */
+    fun pairFromQr(qrRawValue: String) {
+        val payload = try {
+            payloadAdapter.fromJson(qrRawValue)
+        } catch (_: JsonDataException) {
+            null
+        } catch (_: java.io.IOException) {
+            null
+        }
+        if (payload == null) {
+            _state.value = SetupState.Error(SetupError.InvalidQr)
+            return
+        }
+        pairWith(payload)
     }
 
-    val isDeviceSetUp: Flow<Boolean> = dataStore.data.map { prefs ->
-        prefs[IS_SET_UP] ?: false
+    /** Manual entry path — same flow as [pairFromQr] but with a hand-typed payload.
+     *
+     * Used during dev/testing when there is no QR generator handy. Production
+     * users always pair via the QR. ``storeId`` is required because the device
+     * needs the numeric id alongside the code (some endpoints use one, some
+     * use the other).
+     */
+    fun pairManually(apiUrl: String, storeId: Int, storeCode: String, authToken: String) {
+        if (apiUrl.isBlank() || storeCode.isBlank() || authToken.isBlank() || storeId <= 0) {
+            _state.value = SetupState.Error(SetupError.InvalidQr)
+            return
+        }
+        pairWith(
+            SetupPayload(
+                api_url = apiUrl,
+                store_id = storeId,
+                store_code = storeCode,
+                store_name = null,
+                auth_token = authToken,
+            )
+        )
+    }
+
+    fun resetError() {
+        if (_state.value is SetupState.Error) _state.value = SetupState.Idle
+    }
+
+    private fun pairWith(payload: SetupPayload) {
+        _state.value = SetupState.Connecting
+        viewModelScope.launch {
+            // 1. Persist the pairing FIRST so the AuthInterceptor will use the new
+            //    api_url and bearer token on the verification call below.
+            configRepository.savePairing(
+                apiUrl = payload.api_url,
+                authToken = payload.auth_token,
+                storeId = payload.store_id,
+                storeCode = payload.store_code,
+                storeName = payload.store_name,
+            )
+
+            // 2. Verify by hitting /program. Failure → roll back the pairing
+            //    so the user is back at a clean Setup screen with an error.
+            val program: ProgramResponse = try {
+                api.getProgram()
+            } catch (e: Exception) {
+                configRepository.resetDevice()
+                _state.value = SetupState.Error(SetupError.ConnectionFailed(e.message))
+                return@launch
+            }
+
+            configRepository.saveProgram(programAdapter.toJson(program))
+
+            // 4. Warm caches. Failures here are non-fatal — the screens will
+            //    refresh on their own when needed.
+            runCatching { staffPinRepository.refresh() }
+            runCatching { categoryRepository.refresh() }
+
+            _state.value = SetupState.Success
+        }
     }
 }
+
+sealed interface SetupState {
+    data object Idle : SetupState
+    data object Connecting : SetupState
+    data object Success : SetupState
+    data class Error(val reason: SetupError) : SetupState
+}
+
+sealed interface SetupError {
+    data object InvalidQr : SetupError
+    data class ConnectionFailed(val detail: String?) : SetupError
+}