折痕不压字

// gradle/libs.versions.toml —— 版本照 codelab
window = "1.5.1"
androidx-window = { module = "androidx.window:window", version.ref = "window" }
androidx-window-testing = { module = "androidx.window:window-testing", version.ref = "window" }

// ui/components/Window.kt
@Immutable
data class Fold(
    val bounds: DpRect,          // 窗口坐标，宽或高为 0 时按 1px 算
    val vertical: Boolean,       // orientation == VERTICAL
    val halfOpened: Boolean,     // state == HALF_OPENED
    val separating: Boolean,     // isSeparating
    val occluding: Boolean,      // occlusionType == FULL
)

enum class Posture { Normal, Flat, Book, Tabletop }

data class AppWindow(val kind: DeviceKind, val widthDp: Int, val heightDp: Int, val fold: Fold? = null) {
    val posture get() = when {
        fold == null -> Posture.Normal
        !fold.separating -> Posture.Flat
        fold.vertical -> Posture.Book          // 半开书本，或双竖
        else -> Posture.Tabletop               // 半开桌面，或双横
    }
    /** 矮窗口：分屏后的小窗，播放页换紧凑布局。 */
    val short get() = kind == DeviceKind.Phone && heightDp < 480
}

// MainActivity：照 codelab 在 STARTED 期间收集，每次发值都重排
private val layoutInfo = MutableStateFlow(WindowLayoutInfo(emptyList()))

override fun onCreate(savedInstanceState: Bundle?) {
    ...
    lifecycleScope.launch {
        lifecycle.repeatOnLifecycle(Lifecycle.State.STARTED) {
            WindowInfoTracker.getOrCreate(this@MainActivity)
                .windowLayoutInfo(this@MainActivity)
                .collect { layoutInfo.value = it }
        }
    }
}
// rememberAppWindow(layout, layoutInfo)：取第一条 FoldingFeature，bounds 用 density 换成 dp

// ui/adaptive/FoldSplit.kt —— 纯函数，JVM 单测，和 WallGeometry 一样
/** 在自己的窗口矩形 [self] 里，按 [fold] 分出的两块；不相交、或 fold 不分页时返回 null。 */
internal fun foldSplit(self: DpRect, fold: Fold?, margin: Dp = 16.dp): FoldSplit?

// 两个布局原语：用 onPlaced 记下自己在窗口里的位置，交给 foldSplit
@Composable fun FoldRow(start: @Composable () -> Unit, end: @Composable () -> Unit)   // 书本 / 双竖
@Composable fun FoldColumn(top: @Composable () -> Unit, bottom: @Composable () -> Unit) // 桌面 / 双横

// androidTest：照 codelab 用 WindowLayoutInfoPublisherRule 套在 ActivityScenarioRule 外面
private val activityRule = ActivityScenarioRule(MainActivity::class.java)
private val publisherRule = WindowLayoutInfoPublisherRule()
@get:Rule val testRule: TestRule = RuleChain.outerRule(publisherRule).around(activityRule)

@Test fun lyrics_are_right_of_vertical_fold() {
    activityRule.scenario.onActivity { activity ->
        val fold = FoldingFeature(activity = activity, state = HALF_OPENED, orientation = VERTICAL, size = 0)
        publisherRule.overrideWindowLayoutInfo(TestWindowLayoutInfo(listOf(fold)))
    }
    // 断言：歌词栏的左边界在折痕右边
}