diff --git a/superpowers/plans/2026-09-10-ring-health-app-m0-m1.md b/superpowers/plans/2026-09-10-ring-health-app-m0-m1.md
index 39a8307..b36cdcb 100644
--- a/superpowers/plans/2026-09-10-ring-health-app-m0-m1.md
+++ b/superpowers/plans/2026-09-10-ring-health-app-m0-m1.md
@@ -3117,7 +3117,92 @@ git add -A && git commit -m "feat: 实现运动页与运动历史子页"
   - `class DeviceViewModel(ringDeviceRepository)` 暴露 `uiState: StateFlow<DeviceUiState>`、`fun setFunctionEnabled(id: String, enabled: Boolean)`
   - `@Composable fun DeviceScreen(onOpenSettings: () -> Unit, modifier, viewModel)`、`@Composable fun DeviceSettingsScreen(modifier, viewModel)`
 
-- [ ] **Step 1: 写 `DeviceViewModel.kt`**
+- [ ] **Step 1: 写失败的测试**
+
+`app/src/test/java/com/placeholder/ringhealth/feature/device/DeviceViewModelTest.kt`
+（与 Task 8 / Task 9 的两个 ViewModel 测试同形；ledger Ruling R27 —— 三个 ViewModel 的覆盖度应当一致）：
+
+```kotlin
+package com.placeholder.ringhealth.feature.device
+
+import com.placeholder.ringhealth.data.mock.MockRingDeviceRepository
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.ExperimentalCoroutinesApi
+import kotlinx.coroutines.launch
+import kotlinx.coroutines.test.StandardTestDispatcher
+import kotlinx.coroutines.test.advanceUntilIdle
+import kotlinx.coroutines.test.resetMain
+import kotlinx.coroutines.test.runTest
+import kotlinx.coroutines.test.setMain
+import org.junit.After
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertFalse
+import org.junit.Assert.assertTrue
+import org.junit.Before
+import org.junit.Test
+
+/** 设备页 ViewModel 测试。 */
+@OptIn(ExperimentalCoroutinesApi::class)
+class DeviceViewModelTest {
+
+    private val dispatcher = StandardTestDispatcher()
+
+    @Before
+    fun setUp() {
+        Dispatchers.setMain(dispatcher)
+    }
+
+    @After
+    fun tearDown() {
+        Dispatchers.resetMain()
+    }
+
+    @Test
+    fun `输出设备状态与五个功能开关`() = runTest(dispatcher) {
+        val viewModel = DeviceViewModel(MockRingDeviceRepository())
+        backgroundScope.launch { viewModel.uiState.collect {} }
+
+        advanceUntilIdle()
+
+        val state = viewModel.uiState.value
+        assertEquals(78, state.device.batteryPercent)
+        assertEquals("1.0.5", state.device.firmwareVersion)
+        assertEquals(5, state.settings.size)
+    }
+
+    @Test
+    fun `setFunctionEnabled 只改目标项且可来回切换`() = runTest(dispatcher) {
+        val viewModel = DeviceViewModel(MockRingDeviceRepository())
+        backgroundScope.launch { viewModel.uiState.collect {} }
+        advanceUntilIdle()
+
+        // Mock 的 5 项里只有 stress 与 blood_pressure 初始为 false，其余 3 项为 true
+        // （见 MockDataProvider.defaultFunctionSettings）。切换 stress 后应为 4 项开启。
+        val target = "stress"
+        assertFalse(viewModel.uiState.value.settings.first { it.id == target }.enabled)
+
+        viewModel.setFunctionEnabled(target, true)
+        advanceUntilIdle()
+        assertTrue(viewModel.uiState.value.settings.first { it.id == target }.enabled)
+        // 关键：其它开关不受影响。只断言目标项变了，无法发现「整表被覆盖」这类回归。
+        assertEquals(4, viewModel.uiState.value.settings.count { it.enabled })
+
+        viewModel.setFunctionEnabled(target, false)
+        advanceUntilIdle()
+        assertFalse(viewModel.uiState.value.settings.first { it.id == target }.enabled)
+    }
+}
+```
+
+- [ ] **Step 1b: 运行测试，确认失败**
+
+```bash
+cd /d/cherry/repos/ring-health-app && ./gradlew :app:testDebugUnitTest --tests "com.placeholder.ringhealth.feature.device.DeviceViewModelTest"
+```
+
+Expected: `Unresolved reference: DeviceViewModel`，编译失败。
+
+- [ ] **Step 2: 写 `DeviceViewModel.kt`**
 
 ```kotlin
 package com.placeholder.ringhealth.feature.device
@@ -3168,7 +3253,7 @@ class DeviceViewModel(
 }
 ```
 
-- [ ] **Step 1b: 把 `DeviceViewModel` 注册到 `AppViewModelProvider`**
+- [ ] **Step 3: 把 `DeviceViewModel` 注册到 `AppViewModelProvider`**
 
 在 `AppViewModelProvider.kt` 的 `viewModelFactory { }` 内**追加**一个 `initializer`（ledger Ruling R2），
 并在该文件顶部加 `import com.placeholder.ringhealth.feature.device.DeviceViewModel`：
@@ -3184,25 +3269,28 @@ class DeviceViewModel(
 - [ ] **Step 4: 追加文案到 `strings.xml`**
 
 ```xml
-    <string name="device_title">我的设备</string>
     <string name="device_connected">已连接</string>
     <string name="device_disconnected">未连接</string>
     <string name="device_battery">电量 %1$d%%</string>
     <string name="device_firmware">固件版本 %1$s</string>
-    <string name="device_charging">充电中</string>
     <string name="device_settings_title">功能设置</string>
-    <string name="device_find_ring">查找戒指</string>
-    <string name="device_find_ring_desc">让戒指震动以便寻找</string>
-    <string name="device_firmware_update">固件升级</string>
-    <string name="device_firmware_update_desc">检查并升级到最新固件</string>
-    <string name="device_wear_detection">佩戴检测</string>
-    <string name="device_wear_detection_desc">未佩戴时暂停测量</string>
     <string name="device_more">更多设置</string>
     <string name="device_switch_on">已开启</string>
     <string name="device_switch_off">已关闭</string>
 ```
 
-- [ ] **Step 3: 实现 `DeviceScreen.kt`**
+> **本任务不得新增无消费者的字符串资源（ledger Ruling R27）。** 计划早期版本的这份清单有 16 条，
+> 逐条 grep 调用点后砍到 8 条。被删的 8 条是
+> `device_title`（`我的设备`）、`device_charging`（`充电中`）、
+> `device_find_ring` / `device_find_ring_desc`、`device_firmware_update` / `device_firmware_update_desc`、
+> `device_wear_detection` / `device_wear_detection_desc` —— 全计划**零调用点**。
+> 它们看起来是照着小美运动健康的设备页草拟的（查找戒指 / 固件升级 / 佩戴检测三行入口），
+> 但本任务实际实现的设备页只有「戒指信息卡 + 功能开关列表 + 更多设置入口」，
+> 那三行从来没有被写进任何代码。**不要把它们加回来。**
+> 若 M2 真要做「查找戒指」这类入口，那时再补文案 —— 提前写好只会留下 8 条永不渲染的字符串。
+> （`device_settings_hint` 不在此列，它在 Step 5 单独追加，有调用点。）
+
+- [ ] **Step 5: 实现 `DeviceScreen.kt`**
 
 ```kotlin
 package com.placeholder.ringhealth.feature.device
@@ -3219,7 +3307,6 @@ import androidx.compose.foundation.lazy.LazyColumn
 import androidx.compose.foundation.lazy.items
 import androidx.compose.material.icons.Icons
 import androidx.compose.material.icons.filled.Bluetooth
-import androidx.compose.material.icons.filled.Settings
 import androidx.compose.material.icons.filled.Watch
 import androidx.compose.material3.Icon
 import androidx.compose.material3.MaterialTheme
@@ -3230,16 +3317,19 @@ import androidx.compose.runtime.getValue
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.res.stringResource
+import androidx.compose.ui.tooling.preview.Preview
 import androidx.compose.ui.unit.dp
 import androidx.lifecycle.compose.collectAsStateWithLifecycle
 import androidx.lifecycle.viewmodel.compose.viewModel
 import com.placeholder.ringhealth.AppViewModelProvider
 import com.placeholder.ringhealth.R
 import com.placeholder.ringhealth.core.designsystem.MetricGreen
+import com.placeholder.ringhealth.core.designsystem.RingHealthTheme
 import com.placeholder.ringhealth.core.designsystem.TextSecondary
 import com.placeholder.ringhealth.core.designsystem.component.HealthCard
 import com.placeholder.ringhealth.core.designsystem.component.SectionHeader
 import com.placeholder.ringhealth.domain.model.DeviceFunctionSetting
+import com.placeholder.ringhealth.domain.model.RingDeviceState
 
 /** 设备（戒指管理）页。 */
 @Composable
@@ -3352,9 +3442,47 @@ internal fun SettingRow(setting: DeviceFunctionSetting, modifier: Modifier = Mod
         }
     }
 }
+
+@Preview(showBackground = true)
+@Composable
+private fun DeviceContentPreview() {
+    RingHealthTheme {
+        DeviceContent(
+            state = DeviceUiState(
+                device = RingDeviceState(true, "RingHealth 智能戒指", 78, "1.0.5", false),
+                settings = previewSettings(),
+            ),
+            onOpenSettings = {},
+        )
+    }
+}
+
+/**
+ * Preview 用的假开关列表。
+ *
+ * `internal` 而非 `private`：`DeviceSettingsScreen.kt` 的 Preview 也要用。
+ * 取值与 `MockDataProvider.defaultFunctionSettings()` 保持一致，
+ * 免得 Preview 里看到的和跑起来看到的不是同一份数据。
+ */
+internal fun previewSettings(): List<DeviceFunctionSetting> = listOf(
+    DeviceFunctionSetting("heart_rate", "自动心率监测", "每 10 分钟测量一次", true),
+    DeviceFunctionSetting("blood_oxygen", "自动血氧监测", "夜间持续监测", true),
+    DeviceFunctionSetting("sleep", "睡眠监测", "自动识别睡眠时段", true),
+    DeviceFunctionSetting("stress", "压力监测", "全天候压力评估", false),
+    DeviceFunctionSetting("blood_pressure", "血压监测", "需在 App 内手动校准", false),
+)
 ```
 
-- [ ] **Step 4: 实现 `DeviceSettingsScreen.kt`（替换占位）**
+> `previewSettings()` 是**唯一**的例外：它是 `internal` 而不是 `private`，因为两个页面的 Preview 共用。
+> 它只在 Preview 与 debug 构建里被调用，不进任何生产路径。
+
+> **Preview 是本项目唯一可用的目视检查手段（ledger Ruling R21 / R26）**：本机没有模拟器镜像也没有真机，
+> `assembleDebug` 只能证明「能编译」。因此每个页面都必须拆成「公开的有状态外壳 + `private` 的无状态
+> `XContent` + 挂在 `XContent` 上的 `@Preview`」——只有无状态的那层才能喂假数据渲染。
+> 两个页面的 Preview 共用同一个 `internal fun previewSettings()`（定义在 `DeviceScreen.kt` 末尾，
+> 见本步代码块之后）：`DeviceSettingsScreen.kt` 也要用它，`private` 在文件之间传不过去。
+
+- [ ] **Step 6: 实现 `DeviceSettingsScreen.kt`（替换占位）**
 
 ```kotlin
 package com.placeholder.ringhealth.feature.device
@@ -3370,18 +3498,21 @@ import androidx.compose.foundation.lazy.LazyColumn
 import androidx.compose.foundation.lazy.items
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.Switch
+import androidx.compose.material3.SwitchDefaults
 import androidx.compose.material3.Text
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.getValue
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.res.stringResource
+import androidx.compose.ui.tooling.preview.Preview
 import androidx.compose.ui.unit.dp
 import androidx.lifecycle.compose.collectAsStateWithLifecycle
 import androidx.lifecycle.viewmodel.compose.viewModel
 import com.placeholder.ringhealth.AppViewModelProvider
 import com.placeholder.ringhealth.R
 import com.placeholder.ringhealth.core.designsystem.MetricGreen
+import com.placeholder.ringhealth.core.designsystem.RingHealthTheme
 import com.placeholder.ringhealth.core.designsystem.TextSecondary
 import com.placeholder.ringhealth.core.designsystem.component.HealthCard
 import com.placeholder.ringhealth.core.designsystem.component.SectionHeader
@@ -3396,13 +3527,32 @@ fun DeviceSettingsScreen(
     viewModel: DeviceViewModel = viewModel(factory = AppViewModelProvider.Factory),
 ) {
     val state by viewModel.uiState.collectAsStateWithLifecycle()
+    DeviceSettingsContent(
+        settings = state.settings,
+        onToggle = viewModel::setFunctionEnabled,
+        modifier = modifier,
+    )
+}
+
+/**
+ * 无状态设备设置内容。
+ * 与 `DeviceContent` 同样拆出独立函数，Preview 才能喂假数据渲染（ledger Ruling R26）。
+ * 注意回调签名是 `(id, enabled)` 而不是 `(DeviceFunctionSetting, Boolean)`：
+ * 无状态层不该知道「怎么改」，只负责把「改哪一项、改成什么」报上去。
+ */
+@Composable
+private fun DeviceSettingsContent(
+    settings: List<DeviceFunctionSetting>,
+    onToggle: (String, Boolean) -> Unit,
+    modifier: Modifier = Modifier,
+) {
     LazyColumn(
         modifier = modifier.fillMaxSize(),
         contentPadding = PaddingValues(16.dp),
         verticalArrangement = Arrangement.spacedBy(12.dp),
     ) {
         item { SectionHeader(title = stringResource(R.string.device_settings_title)) }
-        items(state.settings) { setting ->
+        items(settings) { setting ->
             HealthCard {
                 Row(
                     modifier = Modifier.fillMaxWidth(),
@@ -3415,8 +3565,9 @@ fun DeviceSettingsScreen(
                     }
                     Switch(
                         checked = setting.enabled,
-                        onCheckedChange = { checked -> viewModel.setFunctionEnabled(setting.id, checked) },
-                        colors = androidx.compose.material3.SwitchDefaults.colors(checkedTrackColor = MetricGreen),
+                        onCheckedChange = { checked -> onToggle(setting.id, checked) },
+                        // SwitchDefaults 走正常 import，不写字面量全限定名（与其余文件的 import 风格一致）
+                        colors = SwitchDefaults.colors(checkedTrackColor = MetricGreen),
                     )
                 }
             }
@@ -3431,15 +3582,23 @@ fun DeviceSettingsScreen(
         }
     }
 }
+
+@Preview(showBackground = true)
+@Composable
+private fun DeviceSettingsContentPreview() {
+    RingHealthTheme {
+        DeviceSettingsContent(settings = previewSettings(), onToggle = { _, _ -> })
+    }
+}
 ```
 
-- [ ] **Step 5: 追加提示文案到 `strings.xml`**
+- [ ] **Step 7: 追加提示文案到 `strings.xml`**
 
 ```xml
     <string name="device_settings_hint">阶段一为演示开关，接入戒指后将同步到设备。</string>
 ```
 
-- [ ] **Step 6: 在 `RingHealthApp.kt` 接入真实页面**
+- [ ] **Step 8: 在 `RingHealthApp.kt` 接入真实页面**
 
 ```kotlin
             composable(Routes.DEVICE) {
@@ -3452,15 +3611,22 @@ fun DeviceSettingsScreen(
 
 删除 `DeviceSettingsPlaceholder` 的定义与 import。
 
-- [ ] **Step 7: 构建 + 验证**
+- [ ] **Step 9: 构建 + 单测**
 
 ```bash
-cd /d/cherry/repos/ring-health-app && ./gradlew assembleDebug
+cd /d/cherry/repos/ring-health-app && ./gradlew :app:testDebugUnitTest && ./gradlew assembleDebug
 ```
 
-Expected: 设备 Tab 显示戒指卡片（电量 78%、固件 1.0.5）；“更多设置”进入后开关可切换且返回后状态保持。
+Expected: 两条命令均 `BUILD SUCCESSFUL`；`DeviceViewModelTest` 由 Step 1b 的 RED 转为 GREEN，
+全量测试 15 项通过（Task 9 之后是 13 项，本任务 +2）。
 
-- [ ] **Step 8: Commit**
+界面上「设备 Tab 显示戒指卡片（电量 78%、固件 1.0.5）」「更多设置进入后开关可切换且返回后状态保持」
+这两条**不在本步验证**（ledger Ruling R21：本机无模拟器与真机），顺延到 Task 14 Step 3 的人工验收清单。
+
+> **不要用 `FROM-CACHE` 的绿当作证据。** Task 9 的修复轮实测到：Gradle 构建缓存命中时
+> 任务会直接标记为 `FROM-CACHE` 而不真正执行。若看到 `FROM-CACHE`，加 `--rerun` 重跑一次再下结论。
+
+- [ ] **Step 10: Commit**
 
 ```bash
 git add -A && git commit -m "feat: 实现设备页与设备设置子页（可交互开关）"