feat(android-terminal): Phase D.4 — enrollment dialog + QR scanner overlay

Both left-pane buttons now functional. Cashier can find a customer by
scanning their loyalty QR or enroll a brand-new customer from the
tablet — closing the last gap in the everyday POS flow.

- TerminalViewModel: scannerOpen / enrollDialogOpen / enrolling /
  enrollError state. submitEnroll posts to /cards/enroll, then re-fetches
  the lookup shape so the customer pane renders fully (rewards,
  cooldown). On lookup-after-enroll failure (rare) the new card_number
  is pre-filled in the search field as a fallback.
- EnrollDialog.kt (new): AlertDialog with name + email (required), phone
  + birthday (optional; birthday is plain YYYY-MM-DD text — date picker
  is a polish task). Inline error surface for backend rejections.
- QrScannerOverlay.kt (new): fullscreen overlay reusing QrScannerView
  from Phase B. Cancel button top-right. Decoded value is treated as a
  card_number and feeds the lookup flow.
- TerminalScreen: scan/enroll buttons are no longer disabled; the two
  new composables render conditionally on top of the main layout.

The tablet now supports every everyday flow: lookup, scan, enroll,
stamp, earn points, redeem stamps, redeem reward, recent feed.

Verified by ./gradlew assembleDebug — clean build.

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

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

@@ -0,0 +1,123 @@
+package lu.rewardflow.terminal.ui.terminal
+
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.Spacer
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.height
+import androidx.compose.foundation.layout.size
+import androidx.compose.foundation.text.KeyboardOptions
+import androidx.compose.material3.AlertDialog
+import androidx.compose.material3.CircularProgressIndicator
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.OutlinedTextField
+import androidx.compose.material3.Text
+import androidx.compose.material3.TextButton
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.res.stringResource
+import androidx.compose.ui.text.input.KeyboardType
+import androidx.compose.ui.unit.dp
+import lu.rewardflow.terminal.R
+
+/**
+ * Bottom-sheet-style enrollment dialog fired from the left-pane
+ * "Enroll Customer" button.
+ *
+ * Required: name + email. Phone + birthday are optional. Birthday
+ * format mirrors what the backend expects (``YYYY-MM-DD`` string) —
+ * the field is plain text for now; a date picker is a polish task.
+ */
+@Composable
+fun EnrollDialog(
+    inProgress: Boolean,
+    error: String?,
+    onSubmit: (name: String, email: String, phone: String?, birthday: String?) -> Unit,
+    onDismiss: () -> Unit,
+) {
+    var name by remember { mutableStateOf("") }
+    var email by remember { mutableStateOf("") }
+    var phone by remember { mutableStateOf("") }
+    var birthday by remember { mutableStateOf("") }
+
+    AlertDialog(
+        onDismissRequest = onDismiss,
+        title = { Text(stringResource(R.string.enroll_title)) },
+        text = {
+            Column {
+                OutlinedTextField(
+                    value = name,
+                    onValueChange = { name = it },
+                    label = { Text(stringResource(R.string.enroll_name)) },
+                    singleLine = true,
+                    modifier = Modifier.fillMaxWidth(),
+                )
+                Spacer(Modifier.height(8.dp))
+                OutlinedTextField(
+                    value = email,
+                    onValueChange = { email = it },
+                    label = { Text(stringResource(R.string.enroll_email)) },
+                    singleLine = true,
+                    keyboardOptions = KeyboardOptions(keyboardType = KeyboardType.Email),
+                    modifier = Modifier.fillMaxWidth(),
+                )
+                Spacer(Modifier.height(8.dp))
+                OutlinedTextField(
+                    value = phone,
+                    onValueChange = { phone = it },
+                    label = { Text(stringResource(R.string.enroll_phone)) },
+                    singleLine = true,
+                    keyboardOptions = KeyboardOptions(keyboardType = KeyboardType.Phone),
+                    modifier = Modifier.fillMaxWidth(),
+                )
+                Spacer(Modifier.height(8.dp))
+                OutlinedTextField(
+                    value = birthday,
+                    onValueChange = { input -> birthday = input.filter { it.isDigit() || it == '-' } },
+                    label = { Text(stringResource(R.string.enroll_birthday)) },
+                    placeholder = { Text("YYYY-MM-DD") },
+                    singleLine = true,
+                    modifier = Modifier.fillMaxWidth(),
+                )
+                if (error != null) {
+                    Spacer(Modifier.height(8.dp))
+                    Text(
+                        text = error,
+                        style = MaterialTheme.typography.bodySmall,
+                        color = MaterialTheme.colorScheme.error,
+                    )
+                }
+            }
+        },
+        confirmButton = {
+            TextButton(
+                onClick = {
+                    onSubmit(
+                        name,
+                        email,
+                        phone.takeIf { it.isNotBlank() },
+                        birthday.takeIf { it.isNotBlank() },
+                    )
+                },
+                enabled = !inProgress && name.isNotBlank() && email.isNotBlank(),
+            ) {
+                if (inProgress) {
+                    CircularProgressIndicator(
+                        modifier = Modifier.size(16.dp),
+                        strokeWidth = 2.dp,
+                    )
+                    Spacer(Modifier.size(8.dp))
+                }
+                Text(stringResource(R.string.enroll_submit))
+            }
+        },
+        dismissButton = {
+            TextButton(onClick = onDismiss, enabled = !inProgress) {
+                Text(stringResource(R.string.action_cancel))
+            }
+        },
+    )
+}

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

@@ -0,0 +1,46 @@
+package lu.rewardflow.terminal.ui.terminal
+
+import androidx.compose.foundation.background
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.padding
+import androidx.compose.material3.FilledTonalButton
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.res.stringResource
+import androidx.compose.ui.unit.dp
+import lu.rewardflow.terminal.R
+import lu.rewardflow.terminal.ui.scanner.QrScannerView
+
+/**
+ * Fullscreen QR scanner overlay used to look up a customer card by
+ * scanning the QR printed on it / on their phone.
+ *
+ * Reuses [QrScannerView] from Phase B — same camera permission UX,
+ * same one-shot fire semantics. The Cancel button bails without a scan.
+ */
+@Composable
+fun QrScannerOverlay(
+    onScanned: (String) -> Unit,
+    onCancel: () -> Unit,
+) {
+    Box(
+        modifier = Modifier
+            .fillMaxSize()
+            .background(Color.Black),
+    ) {
+        QrScannerView(onQrScanned = onScanned)
+
+        FilledTonalButton(
+            onClick = onCancel,
+            modifier = Modifier
+                .align(Alignment.TopEnd)
+                .padding(16.dp),
+        ) {
+            Text(stringResource(R.string.action_cancel))
+        }
+    }
+}

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

@@ -84,6 +84,8 @@ fun TerminalScreen(
                 state = state,
                 onSearchChanged = viewModel::onSearchChanged,
                 onSearchSubmit = viewModel::onSearchSubmit,
+                onScanQrClicked = viewModel::openScanner,
+                onEnrollClicked = viewModel::openEnrollDialog,
                 recentTransactions = state.recentTransactions,
             )
             RightPane(
@@ -110,6 +112,22 @@ fun TerminalScreen(
             onSubmitRedeemReward = viewModel::submitRedeemReward,
         )
     }
+
+    if (state.enrollDialogOpen) {
+        EnrollDialog(
+            inProgress = state.enrolling,
+            error = state.enrollError,
+            onSubmit = viewModel::submitEnroll,
+            onDismiss = viewModel::dismissEnrollDialog,
+        )
+    }
+
+    if (state.scannerOpen) {
+        QrScannerOverlay(
+            onScanned = viewModel::onCardQrScanned,
+            onCancel = viewModel::dismissScanner,
+        )
+    }
 }
 
 @Composable
@@ -167,6 +185,8 @@ private fun LeftPane(
     state: TerminalUiState,
     onSearchChanged: (String) -> Unit,
     onSearchSubmit: () -> Unit,
+    onScanQrClicked: () -> Unit,
+    onEnrollClicked: () -> Unit,
     recentTransactions: List<TransactionItem>,
 ) {
     Surface(
@@ -212,10 +232,8 @@ private fun LeftPane(
 
             Spacer(Modifier.height(12.dp))
 
-            // Phase D.4 will replace these with real handlers.
             OutlinedButton(
-                onClick = { /* QR scan — D.4 */ },
+                onClick = onScanQrClicked,
-                enabled = false,
                 modifier = Modifier.fillMaxWidth(),
                 contentPadding = PaddingValues(vertical = 12.dp),
             ) {
@@ -223,8 +241,7 @@ private fun LeftPane(
             }
             Spacer(Modifier.height(8.dp))
             OutlinedButton(
-                onClick = { /* Enroll — D.4 */ },
+                onClick = onEnrollClicked,
-                enabled = false,
                 modifier = Modifier.fillMaxWidth(),
                 contentPadding = PaddingValues(vertical = 12.dp),
             ) {

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

@@ -15,6 +15,7 @@ import kotlinx.coroutines.launch
 import lu.rewardflow.terminal.data.api.LoyaltyApi
 import lu.rewardflow.terminal.data.model.CardLookupResponse
 import lu.rewardflow.terminal.data.model.CategoryItem
+import lu.rewardflow.terminal.data.model.EnrollRequest
 import lu.rewardflow.terminal.data.model.PointsEarnRequest
 import lu.rewardflow.terminal.data.model.PointsRedeemRequest
 import lu.rewardflow.terminal.data.model.ProgramResponse
@@ -102,6 +103,102 @@ class TerminalViewModel @Inject constructor(
         onSearchSubmit()
     }
 
+    // ── Scanner overlay ──────────────────────────────────────────────
+
+    fun openScanner() {
+        _state.value = _state.value.copy(scannerOpen = true, errorMessage = null)
+    }
+
+    fun dismissScanner() {
+        _state.value = _state.value.copy(scannerOpen = false)
+    }
+
+    /** Decoded raw value from the QR scanner overlay. Loyalty card QRs
+     *  encode the card_number, so we hand it straight to the lookup. */
+    fun onCardQrScanned(rawValue: String) {
+        _state.value = _state.value.copy(scannerOpen = false)
+        lookupByCardNumber(rawValue)
+    }
+
+    // ── Enrollment dialog ────────────────────────────────────────────
+
+    fun openEnrollDialog() {
+        _state.value = _state.value.copy(
+            enrollDialogOpen = true,
+            enrolling = false,
+            enrollError = null,
+        )
+    }
+
+    fun dismissEnrollDialog() {
+        _state.value = _state.value.copy(
+            enrollDialogOpen = false,
+            enrolling = false,
+            enrollError = null,
+        )
+    }
+
+    /** Submit the enrollment form. ``birthday`` is expected as an ISO
+     *  ``YYYY-MM-DD`` string or null. The new card is looked up after
+     *  enrollment so the customer pane renders with the full lookup
+     *  shape (rewards, can_stamp, cooldown, etc). */
+    fun submitEnroll(
+        name: String,
+        email: String,
+        phone: String?,
+        birthday: String?,
+    ) {
+        if (_state.value.enrolling) return
+        if (name.isBlank() || email.isBlank()) {
+            _state.value = _state.value.copy(enrollError = "Name and email are required")
+            return
+        }
+        _state.value = _state.value.copy(enrolling = true, enrollError = null)
+        viewModelScope.launch {
+            val result = runCatching {
+                api.enrollCustomer(
+                    EnrollRequest(
+                        email = email.trim(),
+                        customer_name = name.trim(),
+                        customer_phone = phone?.trim()?.takeIf { it.isNotBlank() },
+                        customer_birthday = birthday?.trim()?.takeIf { it.isNotBlank() },
+                    )
+                )
+            }
+            result.fold(
+                onSuccess = { card ->
+                    // Re-fetch with the lookup shape so the customer pane has
+                    // the full set of fields (rewards, cooldown, etc).
+                    runCatching { api.lookupCard(card.card_number) }
+                        .onSuccess { hydrated ->
+                            _state.value = _state.value.copy(
+                                enrolling = false,
+                                enrollDialogOpen = false,
+                                customer = hydrated,
+                            )
+                            refreshRecentTransactions()
+                        }
+                        .onFailure {
+                            // Card was enrolled — but we couldn't fetch the
+                            // hydrated view. Close the dialog anyway and let
+                            // the user search by the new card_number.
+                            _state.value = _state.value.copy(
+                                enrolling = false,
+                                enrollDialogOpen = false,
+                                searchQuery = card.card_number,
+                            )
+                        }
+                },
+                onFailure = { err ->
+                    _state.value = _state.value.copy(
+                        enrolling = false,
+                        enrollError = err.message ?: "Enrollment failed",
+                    )
+                },
+            )
+        }
+    }
+
     fun clearCustomer() {
         _state.value = _state.value.copy(
             customer = null,
@@ -263,6 +360,10 @@ data class TerminalUiState(
     val actionInProgress: Boolean = false,
     val actionResult: ActionResult? = null,
     val recentTransactions: List<TransactionItem> = emptyList(),
+    val scannerOpen: Boolean = false,
+    val enrollDialogOpen: Boolean = false,
+    val enrolling: Boolean = false,
+    val enrollError: String? = null,
 )
 
 enum class ActionKind { AddStamp, EarnPoints, RedeemStamps, RedeemReward }