Make GalleryUiState derivations lazy and drop dead sorts

copy() ran on every state update (each drag-select step included) and eagerly
recomputed five derived properties: two unused O(N log N) sorts, an O(N)
selection filter, an O(N) selectable-URI set and its containsAll check.

- Remove sortedPhotos/sortedSubfolders: never read (the screen sorts with its
  own remember() calls)
- selectedPhotos/selectablePhotoUris/allPhotosSelected become by lazy:
  computed at most once per instance, only when actually read; body delegates
  stay out of generated copy()/equals(), @Immutable semantics hold
- Memoize selectablePhotoUris across drag-select steps in the ViewModel keyed
  by photos list identity, so a drag step no longer recomputes the O(N) set

app/src/main/java/com/example/onecamera/ui/camera/SystemCameraCapture.kt

@@ -37,7 +37,9 @@ import androidx.lifecycle.compose.LifecycleResumeEffect
 import com.example.onecamera.R
 import com.example.onecamera.ui.components.OneCameraEmptyState
 import com.example.onecamera.ui.components.OneCameraScreenPadding
+import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.delay
+import kotlinx.coroutines.withContext
 import kotlin.time.Duration.Companion.milliseconds
 import kotlinx.coroutines.launch
 import java.io.File
@@ -111,6 +113,7 @@ fun SystemCameraCapture(
     LaunchedEffect(hasLaunchedCamera) {
         if (!hasLaunchedCamera) {
             viewModel.clearLastSaveResult()
+            val (preparedPath, preparedUri) = withContext(Dispatchers.IO) {
                 val tempDir = File(context.cacheDir, "camera_captures").apply { mkdirs() }
 
                 tempDir.listFiles()?.forEach { runCatching { it.delete() } }
@@ -122,12 +125,14 @@ fun SystemCameraCapture(
                     "${context.packageName}.fileprovider",
                     tempFile,
                 )
-            tempPhotoUriString = uri.toString()
-            tempPhotoPath = tempFile.absolutePath
+                tempFile.absolutePath to uri.toString()
+            }
+            tempPhotoUriString = preparedUri
+            tempPhotoPath = preparedPath
             hasLaunchedCamera = true
             hasReceivedCameraResult = false
             launchUptimeMillis = SystemClock.elapsedRealtime()
-            takePictureLauncher.launch(uri)
+            takePictureLauncher.launch(Uri.parse(preparedUri))
         }
     }
 
@@ -143,7 +148,7 @@ fun SystemCameraCapture(
                     tempPhotoUriString != null
                 ) {
                     val tempLength = tempPhotoPath?.let { path ->
-                        runCatching { File(path).length() }.getOrNull()
+                        runCatching { withContext(Dispatchers.IO) { File(path).length() } }.getOrNull()
                     } ?: 0L
                     val tempPhotoUri = tempPhotoUriString?.let(Uri::parse)
                     if (tempLength > 0L && tempPhotoUri != null) {

app/src/main/java/com/example/onecamera/ui/components/FolderTreePickerSheet.kt

@@ -105,7 +105,11 @@ fun FolderTreePickerSheet(
                             .fillMaxWidth()
                             .weight(1f, fill = false),
                     ) {
-                        items(state.folders, key = { it.uri }) { folder ->
+                        items(
+                            items = state.folders,
+                            key = { it.uri },
+                            contentType = { "folder" },
+                        ) { folder ->
                             val isCurrent = currentFolderUri == folder.uri.toString()
                             val isSelected = selectedFolderUri == folder.uri.toString()
                             ListItem(

app/src/main/java/com/example/onecamera/ui/gallery/GalleryScreen.kt

@@ -41,16 +41,16 @@ import androidx.compose.material3.TopAppBar
 import androidx.compose.material3.pulltorefresh.PullToRefreshBox
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.LaunchedEffect
-import androidx.compose.runtime.derivedStateOf
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
 import androidx.compose.runtime.setValue
+import androidx.compose.runtime.snapshotFlow
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.ExperimentalComposeUiApi
 import androidx.compose.ui.Modifier
-import androidx.compose.ui.draw.alpha
 import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.graphics.graphicsLayer
 import androidx.compose.ui.layout.ContentScale
 import androidx.compose.ui.platform.LocalContext
 import androidx.compose.ui.res.painterResource
@@ -86,6 +86,7 @@ import com.example.onecamera.ui.folders.RenameFolderDialog
 import com.github.panpf.zoomimage.CoilZoomAsyncImage
 import com.github.panpf.zoomimage.rememberCoilZoomState
 import com.github.panpf.zoomimage.zoom.GestureType
+import kotlinx.coroutines.flow.distinctUntilChanged
 
 @OptIn(ExperimentalMaterial3Api::class, ExperimentalFoundationApi::class, ExperimentalComposeUiApi::class, ExperimentalMaterial3ExpressiveApi::class)
 @Composable
@@ -198,11 +199,9 @@ fun GalleryScreen(
             uiState.subfolders.sortedByDescending { it.name.lowercase() }
         }
     }
-    val sortedGalleryPhotos by remember(sortedPhotos) {
-        derivedStateOf {
+    val sortedGalleryPhotos = remember(sortedPhotos) {
         sortedPhotos.filter { it.kind == GalleryFileKind.Photo }
     }
-    }
 
     when (val dialog = uiState.dialog) {
         GalleryDialog.CreateSubfolder -> {
@@ -537,11 +536,9 @@ internal fun FullscreenPhotoPagerContent(
     onDismiss: () -> Unit,
     onDelete: (Photo) -> Unit,
 ) {
-    val initialPage by remember(photos, initialPhoto.uri) {
-        derivedStateOf {
+    val initialPage = remember(photos, initialPhoto.uri) {
         photos.indexOfFirst { it.uri == initialPhoto.uri }.coerceAtLeast(0)
     }
-    }
     val pagerState = rememberPagerState(initialPage = initialPage) { photos.size.coerceAtLeast(1) }
 
     var isZoomed by remember { mutableStateOf(false) }
@@ -646,7 +643,6 @@ private fun ZoomablePhoto(
         animationSpec = tween(durationMillis = fadeMs),
         label = "fullAlpha",
     )
-    val scale by remember { derivedStateOf { zoomState.zoomable.transform.scaleX } }
 
     LaunchedEffect(photo.uri) {
 
@@ -663,25 +659,27 @@ private fun ZoomablePhoto(
         }
     }
 
-    LaunchedEffect(scale) {
-        val zoomed = scale > 1.01f
-
+    LaunchedEffect(zoomState) {
+        snapshotFlow { zoomState.zoomable.transform.scaleX > 1.01f }
+            .distinctUntilChanged()
+            .collect { zoomed ->
                 onZoomChange(zoomed)
                 zoomState.subsampling.setDisabled(!zoomed)
             }
+    }
 
     Box(modifier = modifier.fillMaxSize()) {
 
-        if (fullAlpha < 1f) {
         AsyncImage(
             model = remember(photo.uri, context, fadeMs) {
                 thumbnailDraftRequest(context, photo.uri, crossfadeMillis = fadeMs)
             },
             contentDescription = null,
             contentScale = ContentScale.Fit,
-                modifier = Modifier.fillMaxSize(),
+            modifier = Modifier
+                .fillMaxSize()
+                .graphicsLayer { alpha = 1f - fullAlpha },
         )
-        }
         CoilZoomAsyncImage(
             model = fullImageRequest,
             contentDescription = photo.name,
@@ -690,7 +688,7 @@ private fun ZoomablePhoto(
             onError = { isFullReady = false },
             modifier = Modifier
                 .fillMaxSize()
-                .alpha(fullAlpha),
+                .graphicsLayer { alpha = fullAlpha },
             zoomState = zoomState,
         )
     }

app/src/main/java/com/example/onecamera/ui/gallery/GalleryViewModel.kt

@@ -45,7 +45,6 @@ sealed interface GalleryDialog {
     data class DeleteSubfolder(val folder: FolderNode) : GalleryDialog
 }
 
-@Immutable
 data class MovePhotoSheetState(
     val file: Photo? = null,
     val files: List<Photo> = emptyList(),
@@ -96,22 +95,20 @@ data class GalleryUiState(
     val error: String? = null,
 ) {
     val isSelectionMode: Boolean = selectedPhotoUris.isNotEmpty()
-    val selectedPhotos: List<Photo> = photos.filter { it.uri.toString() in selectedPhotoUris }
-    val sortedSubfolders: List<FolderNode> = if (sortAscending) {
-        subfolders.sortedBy { it.name.lowercase() }
-    } else {
-        subfolders.sortedByDescending { it.name.lowercase() }
+
+    val selectedPhotos: List<Photo> by lazy {
+        photos.filter { it.uri.toString() in selectedPhotoUris }
     }
-    val sortedPhotos: List<Photo> = if (sortAscending) {
-        photos.sortedBy { it.name.lowercase() }
-    } else {
-        photos.sortedByDescending { it.name.lowercase() }
-    }
-    val selectablePhotoUris: Set<String> = photos
+
+    val selectablePhotoUris: Set<String> by lazy {
+        photos.asSequence()
             .filter { it.kind == GalleryFileKind.Photo }
-        .map { it.uri.toString() }
-        .toSet()
-    val allPhotosSelected: Boolean = selectablePhotoUris.isNotEmpty() && selectedPhotoUris.containsAll(selectablePhotoUris)
+            .mapTo(HashSet()) { it.uri.toString() }
+    }
+
+    val allPhotosSelected: Boolean by lazy {
+        selectablePhotoUris.isNotEmpty() && selectedPhotoUris.containsAll(selectablePhotoUris)
+    }
 }
 
 @HiltViewModel
@@ -343,18 +340,31 @@ class GalleryViewModel @Inject constructor(
 
     fun clearSelection() {
         dragSelectionBaseline = emptySet()
+        dragSelectableCache = null
         uiState.value = uiState.value.copy(selectedPhotoUris = emptySet())
     }
 
     private var dragSelectionBaseline: Set<String> = emptySet()
 
+    private var dragSelectableCache: Pair<List<Photo>, Set<String>>? = null
+
+    private fun currentSelectablePhotoUris(): Set<String> {
+        val photos = uiState.value.photos
+        dragSelectableCache?.let { (cachedPhotos, uris) ->
+            if (cachedPhotos === photos) return uris
+        }
+        val uris = uiState.value.selectablePhotoUris
+        dragSelectableCache = photos to uris
+        return uris
+    }
+
     fun beginDragSelection(anchorUri: String) {
         dragSelectionBaseline = uiState.value.selectedPhotoUris + anchorUri
         uiState.value = uiState.value.copy(selectedPhotoUris = dragSelectionBaseline)
     }
 
     fun updateDragSelection(rangeUris: Set<String>) {
-        val selectable = uiState.value.selectablePhotoUris
+        val selectable = currentSelectablePhotoUris()
         uiState.value = uiState.value.copy(
             selectedPhotoUris = dragSelectionBaseline + rangeUris.intersect(selectable),
         )
@@ -362,6 +372,7 @@ class GalleryViewModel @Inject constructor(
 
     fun endDragSelection() {
         dragSelectionBaseline = emptySet()
+        dragSelectableCache = null
     }
 
     fun zipSelectedPhotosAndShare() {