fix(aap): Make AirPods rename actually apply on device

Switch the AAP rename packet to the opcode 0x1A format (04 00 04 00 1A 00 01 [size] 00 [name]) matching the LibrePods documentation and Linux implementation. The previous 0x1E variant (from the LibrePods Android code) was silently ignored by AirPods Pro 2 USB-C firmware — no 0x001D echo, no persistence across reconnect.

Verified on AirPods Pro 2 USB-C (firmware 81.2675...): the device now echoes the new name back via the next 0x001D INFORMATION message, and the name persists after disconnect/reconnect.

Also hardens the rename UX: gate the edit icon on isAapReady (was isAapConnected, which allowed sending during HANDSHAKING), apply an optimistic deviceInfo update with a scoped rollback on send failure, surface send errors via a new Event.SendFailed + snackbar, and restrict dialog input to ASCII with inline error feedback. Unifies send() / sendProGated() through a single sendInternal() helper so error plumbing benefits every command, not just rename.

Note: this only updates the AirPods firmware's self-reported name. Android's system Bluetooth settings read from the bond database and are not affected — renaming there still requires the Android system Bluetooth UI.

app/src/main/java/eu/darken/capod/main/ui/devicesettings/DeviceSettingsScreen.kt

@@ -44,6 +44,8 @@ import androidx.compose.material3.Scaffold
 import androidx.compose.material3.SegmentedButton
 import androidx.compose.material3.SegmentedButtonDefaults
 import androidx.compose.material3.SingleChoiceSegmentedButtonRow
+import androidx.compose.material3.SnackbarHost
+import androidx.compose.material3.SnackbarHostState
 import androidx.compose.material3.Text
 import androidx.compose.material3.TopAppBar
 import androidx.compose.runtime.Composable
@@ -95,12 +97,18 @@ fun DeviceSettingsScreenHost(
     LaunchedEffect(address) { vm.initialize(address) }
 
     val context = LocalContext.current
+    val snackbarHostState = remember { SnackbarHostState() }
     LaunchedEffect(Unit) {
         vm.events.collect { event ->
             when (event) {
                 DeviceSettingsViewModel.Event.OpenBluetoothSettings -> {
                     context.startActivity(Intent(Settings.ACTION_BLUETOOTH_SETTINGS))
                 }
+                is DeviceSettingsViewModel.Event.SendFailed -> {
+                    snackbarHostState.showSnackbar(
+                        context.getString(R.string.device_settings_send_failed, event.message ?: ""),
+                    )
+                }
             }
         }
     }
@@ -110,6 +118,7 @@ fun DeviceSettingsScreenHost(
 
     DeviceSettingsScreen(
         state = currentState,
+        snackbarHostState = snackbarHostState,
         onNavigateUp = { vm.navUp() },
         onAncModeChange = { vm.setAncMode(it) },
         onConversationalAwarenessChange = { vm.setConversationalAwareness(it) },
@@ -137,6 +146,7 @@ fun DeviceSettingsScreenHost(
 @Composable
 fun DeviceSettingsScreen(
     state: DeviceSettingsViewModel.State,
+    snackbarHostState: SnackbarHostState = remember { SnackbarHostState() },
     onNavigateUp: () -> Unit,
     onAncModeChange: (AapSetting.AncMode.Value) -> Unit = {},
     onConversationalAwarenessChange: (Boolean) -> Unit = {},
@@ -195,6 +205,7 @@ fun DeviceSettingsScreen(
                 },
             )
         },
+        snackbarHost = { SnackbarHost(hostState = snackbarHostState) },
     ) { paddingValues ->
         LazyColumn(
             modifier = Modifier.padding(paddingValues),
@@ -216,7 +227,7 @@ fun DeviceSettingsScreen(
                         connectionStateLabel = stateDetection?.state?.getLabel(context),
                         lastSeen = device.lastSeenFormatted(state.now),
                         firstSeen = firstSeen,
-                        canRename = device.isAapConnected,
+                        canRename = device.isAapReady,
                         onRename = onDeviceNameChange,
                     )
                 }
@@ -1010,22 +1021,38 @@ private fun RenameDialog(
 ) {
     var textValue by remember { mutableStateOf(currentName) }
 
+    // The decoder in DefaultAapDeviceProfile only round-trips printable ASCII (0x20..0x7E),
+    // so even if the device accepts a UTF-8 name we can't display it back correctly. Accept any
+    // input up to the 32-byte UX cap, but flag non-ASCII with an inline error so the user
+    // understands why Rename is disabled.
+    val hasInvalidAscii = textValue.any { it.code !in 0x20..0x7E }
+    val isValid = textValue.isNotBlank() && !hasInvalidAscii
+
     androidx.compose.material3.AlertDialog(
         onDismissRequest = onDismiss,
         title = { Text(stringResource(R.string.device_settings_rename_label)) },
         text = {
             androidx.compose.material3.OutlinedTextField(
                 value = textValue,
-                onValueChange = { if (it.length <= 32) textValue = it },
+                onValueChange = { newValue ->
+                    // US_ASCII encoding maps non-ASCII chars to '?' (1 byte each), giving a
+                    // stable upper bound equal to the UTF-16 char count. Keeps the cap the user
+                    // sees consistent regardless of character content.
+                    if (newValue.toByteArray(Charsets.US_ASCII).size <= 32) textValue = newValue
+                },
                 singleLine = true,
                 label = { Text(stringResource(R.string.device_settings_rename_hint)) },
+                isError = hasInvalidAscii,
+                supportingText = if (hasInvalidAscii) {
+                    { Text(stringResource(R.string.device_settings_rename_invalid_ascii)) }
+                } else null,
                 modifier = Modifier.fillMaxWidth(),
             )
         },
         confirmButton = {
             androidx.compose.material3.TextButton(
-                onClick = { if (textValue.isNotBlank()) onConfirm(textValue) },
-                enabled = textValue.isNotBlank() && textValue != currentName,
+                onClick = { if (isValid) onConfirm(textValue) },
+                enabled = isValid && textValue != currentName,
             ) {
                 Text(stringResource(R.string.device_settings_rename_confirm))
             }

app/src/main/java/eu/darken/capod/main/ui/devicesettings/DeviceSettingsViewModel.kt

@@ -57,6 +57,7 @@ class DeviceSettingsViewModel @Inject constructor(
 
     sealed interface Event {
         data object OpenBluetoothSettings : Event
+        data class SendFailed(val command: AapCommand, val message: String?) : Event
     }
 
     val events = SingleEventFlow<Event>()
@@ -130,27 +131,26 @@ class DeviceSettingsViewModel @Inject constructor(
         }
     }
 
-    private fun send(command: AapCommand) {
+    private suspend fun sendInternal(command: AapCommand) {
         val address = targetAddress.value ?: return
-        launch {
-            try {
-                aapManager.sendCommand(address, command)
-                log(TAG) { "Sent $command to $address" }
-            } catch (e: Exception) {
-                log(TAG) { "Failed to send $command: ${e.message}" }
-            }
+        try {
+            aapManager.sendCommand(address, command)
+            log(TAG) { "Sent $command to $address" }
+        } catch (e: Exception) {
+            log(TAG, WARN) { "Failed to send $command: ${e.message}" }
+            // SingleEventFlow is backed by a BUFFERED Channel — use the suspending emit to avoid
+            // dropping the event under momentary backpressure.
+            events.emit(Event.SendFailed(command, e.message))
         }
     }
 
+    private fun send(command: AapCommand) {
+        launch { sendInternal(command) }
+    }
+
     private fun sendProGated(command: AapCommand) = launch {
         if (upgradeRepo.isPro()) {
-            val address = targetAddress.value ?: return@launch
-            try {
-                aapManager.sendCommand(address, command)
-                log(TAG) { "Sent $command to $address" }
-            } catch (e: Exception) {
-                log(TAG) { "Failed to send $command: ${e.message}" }
-            }
+            sendInternal(command)
         } else {
             navTo(Nav.Main.Upgrade)
         }

app/src/main/java/eu/darken/capod/pods/core/apple/aap/AapConnection.kt

@@ -174,8 +174,19 @@ internal class AapConnection(
             }
         }
 
+        val preSendDeviceInfo = currentState.deviceInfo
         applyOptimisticUpdate(currentState, command)
-        sendRaw(command)
+        try {
+            sendRaw(command)
+        } catch (e: Exception) {
+            // Rollback is scoped to rename — the name is the one user-visible writable field
+            // that has no device echo to correct an incorrect optimistic update, so a failed
+            // send would otherwise leave the UI permanently lying about the device name.
+            if (command is AapCommand.SetDeviceName && preSendDeviceInfo != null) {
+                _state.value = _state.value.copy(deviceInfo = preSendDeviceInfo)
+            }
+            throw e
+        }
     }
 
     /**
@@ -244,7 +255,12 @@ internal class AapConnection(
             is AapCommand.SetSleepDetection -> {
                 AapSetting.SleepDetection::class to AapSetting.SleepDetection(enabled = command.enabled)
             }
-            is AapCommand.SetDeviceName -> return // No optimistic state — name comes from deviceInfo
+            is AapCommand.SetDeviceName -> {
+                val currentInfo = baseState.deviceInfo ?: return
+                _state.value = baseState
+                    .copy(deviceInfo = currentInfo.copy(name = command.name), lastMessageAt = Instant.now())
+                return
+            }
         }
         _state.value = baseState.withSetting(updated.first, updated.second).copy(lastMessageAt = Instant.now())
     }

app/src/main/java/eu/darken/capod/pods/core/apple/aap/protocol/DefaultAapDeviceProfile.kt

@@ -449,11 +449,24 @@ class DefaultAapDeviceProfile(
     }
 
     private fun buildRenameMessage(name: String): ByteArray {
+        // Uses the opcode 0x1A format from the LibrePods AAP docs + Linux implementation.
+        // Verified end-to-end on AirPods Pro 2 USB-C (firmware 81.2675...): the device accepts
+        // the rename, persists it, and echoes the new name back via the next 0x001D device info
+        // message on reconnect.
+        //
+        // Note: the LibrePods Android code (AACPManager.createRenamePacket) uses a DIFFERENT
+        // format with opcode 0x1E and a trailing NUL, but on-device testing shows the device
+        // silently ignores that variant. The Linux / documented format is the one that works.
+        //
+        // Scope: this only changes the AirPods firmware's self-reported name (what 0x001D
+        // returns). It does NOT update the phone's Bluetooth alias — Android's system Bluetooth
+        // settings read from the bond database, which is separate and would require
+        // BluetoothDevice.setAlias(). That's intentionally out of scope here.
         val nameBytes = name.toByteArray(Charsets.UTF_8)
         require(nameBytes.size <= 127) { "Device name too long: ${nameBytes.size} bytes (max 127)" }
         return byteArrayOf(
             0x04, 0x00, 0x04, 0x00,
-            0x1E, 0x00,
+            0x1A, 0x00, 0x01,
             nameBytes.size.toByte(), 0x00,
         ) + nameBytes
     }

app/src/main/res/values/strings.xml

@@ -495,6 +495,8 @@
     <string name="device_settings_rename_label">Rename</string>
     <string name="device_settings_rename_hint">Device name</string>
     <string name="device_settings_rename_confirm">Rename</string>
+    <string name="device_settings_rename_invalid_ascii">Only ASCII characters are supported</string>
+    <string name="device_settings_send_failed">Could not apply setting: %1$s</string>
     <string name="device_settings_category_connections_label">Connected Devices</string>
     <string name="device_settings_connected_devices_description">Other devices currently connected to these AirPods</string>
     <string name="device_settings_connected_device_label">Device %d</string>

app/src/test/java/eu/darken/capod/main/ui/devicesettings/DeviceSettingsViewModelTest.kt

@@ -7,11 +7,15 @@ import eu.darken.capod.common.upgrade.UpgradeRepo
 import eu.darken.capod.monitor.core.DeviceMonitor
 import eu.darken.capod.monitor.core.PodDevice
 import eu.darken.capod.pods.core.apple.aap.AapConnectionManager
+import eu.darken.capod.pods.core.apple.aap.protocol.AapCommand
 import io.kotest.matchers.shouldBe
+import io.kotest.matchers.types.shouldBeInstanceOf
+import io.mockk.Called
 import io.mockk.coEvery
 import io.mockk.coVerify
 import io.mockk.every
 import io.mockk.mockk
+import io.mockk.verify
 import kotlinx.coroutines.CompletableDeferred
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.ExperimentalCoroutinesApi
@@ -215,4 +219,46 @@ class DeviceSettingsViewModelTest : BaseTest() {
             coVerify(exactly = 1) { bluetoothManager.nudgeConnection(bonded) }
             vm.state.first().isForceConnecting shouldBe false
         }
+
+    @Test
+    fun `setDeviceName forwards SetDeviceName command to aapManager`() = runTest(testDispatcher) {
+        val vm = createViewModel()
+        vm.initialize(testAddress)
+        vm.state.first()
+
+        vm.setDeviceName("NewName")
+
+        coVerify { aapManager.sendCommand(testAddress, AapCommand.SetDeviceName("NewName")) }
+    }
+
+    @Test
+    fun `setDeviceName when no target address is a no-op`() = runTest(testDispatcher) {
+        val vm = createViewModel()
+        // Intentionally skip initialize — targetAddress stays null.
+
+        vm.setDeviceName("NewName")
+
+        // `any<AapCommand>()` can't be used here (AapCommand is sealed, mockk can't stub it),
+        // so verify the entire manager was not called instead.
+        verify { aapManager wasNot Called }
+    }
+
+    @Test
+    fun `setDeviceName failure emits SendFailed event`() = runTest(testDispatcher) {
+        val failure = IllegalStateException("socket closed")
+        coEvery {
+            aapManager.sendCommand(testAddress, AapCommand.SetDeviceName("NewName"))
+        } throws failure
+
+        val vm = createViewModel()
+        vm.initialize(testAddress)
+        vm.state.first()
+
+        vm.setDeviceName("NewName")
+
+        val event = vm.events.first()
+        val sendFailed = event.shouldBeInstanceOf<DeviceSettingsViewModel.Event.SendFailed>()
+        sendFailed.command shouldBe AapCommand.SetDeviceName("NewName")
+        sendFailed.message shouldBe "socket closed"
+    }
 }

app/src/test/java/eu/darken/capod/pods/core/apple/aap/devices/DefaultAapDeviceProfileNewSettingsTest.kt

@@ -128,16 +128,23 @@ class DefaultAapDeviceProfileNewSettingsTest : BaseAapSessionTest() {
         @Test fun `decode unknown returns null`() { profile.decodeSetting(settingsMessage(0x31, 0x00)).shouldBeNull() }
     }
 
-    // ── Device Rename (0x1E) ────────────────────────────────
+    // ── Device Rename (0x1A) ────────────────────────────────
+    // The working opcode is 0x1A (not the 0x1E variant in LibrePods Android); see the rationale
+    // comment in DefaultAapDeviceProfile.buildRenameMessage for the on-device test details.
 
     @Nested
     inner class DeviceRenameTests {
         @Test
-        fun `encode simple ASCII name`() {
+        fun `encode simple ASCII name full frame`() {
+            // Locks in the full wire format: header + opcode prefix (1A 00 01) + length (LE u16) + name.
             val bytes = profile.encodeCommand(AapCommand.SetDeviceName("MyPods"))
-            bytes[4] shouldBe 0x1E.toByte()
-            bytes[6] shouldBe 6.toByte() // length
-            String(bytes, 8, 6, Charsets.UTF_8) shouldBe "MyPods"
+            val expected = byteArrayOf(
+                0x04, 0x00, 0x04, 0x00,
+                0x1A, 0x00, 0x01,
+                0x06, 0x00,
+                0x4D, 0x79, 0x50, 0x6F, 0x64, 0x73,
+            )
+            bytes shouldBe expected
         }
 
         @Test
@@ -145,8 +152,9 @@ class DefaultAapDeviceProfileNewSettingsTest : BaseAapSessionTest() {
             val name = "AirPods \uD83C\uDFA7" // headphone emoji
             val nameBytes = name.toByteArray(Charsets.UTF_8)
             val bytes = profile.encodeCommand(AapCommand.SetDeviceName(name))
-            bytes[6] shouldBe nameBytes.size.toByte()
-            String(bytes, 8, nameBytes.size, Charsets.UTF_8) shouldBe name
+            bytes.size shouldBe 9 + nameBytes.size
+            bytes[7] shouldBe nameBytes.size.toByte()
+            String(bytes, 9, nameBytes.size, Charsets.UTF_8) shouldBe name
         }
 
         @Test
@@ -159,7 +167,8 @@ class DefaultAapDeviceProfileNewSettingsTest : BaseAapSessionTest() {
         fun `encode accepts 127 byte name`() {
             val name = "A".repeat(127)
             val bytes = profile.encodeCommand(AapCommand.SetDeviceName(name))
-            bytes[6] shouldBe 127.toByte()
+            bytes.size shouldBe 9 + 127
+            bytes[7] shouldBe 127.toByte()
         }
     }