add cancel button to scanner

modules/astra-library-scanner/android/src/androidTest/java/expo/modules/astralibraryscanner/data/RoomLibraryRepositoryTest.kt

@@ -127,6 +127,43 @@ class RoomLibraryRepositoryTest {
     assertNull(dao.getGeneration("active"))
   }
 
+  @Test
+  fun cancelledScanDiscardsStagingAndRestoresFolderWithoutPublishing() = runBlocking {
+    publish("active", listOf(track("active", 1, "Last known good")))
+    val catalogDao = catalog.catalogDao()
+    val userDao = user.userDao()
+    val revision = catalogDao.getRevision()
+    val scannedAt = 1234L
+    val folderId = userDao.insertFolder(
+      FolderEntity(
+        treeUri = "content://music",
+        displayName = "Music",
+        addedAt = 1,
+        lastScannedAt = scannedAt,
+        lastScanStatus = "ready",
+      ),
+    )
+
+    catalogDao.insertGeneration(ScanGenerationEntity("cancelled", "local:1", "staging", 2))
+    catalogDao.putTracks(listOf(track("cancelled", 2, "Half written scan")))
+    userDao.updateFolderScanState(folderId, scannedAt, "scanning", null)
+
+    catalogDao.deleteGenerationTracks("cancelled")
+    catalogDao.deleteGeneration("cancelled")
+    userDao.updateFolderScanState(folderId, scannedAt, "ready", null)
+
+    assertNull(catalogDao.getGeneration("cancelled"))
+    assertEquals(revision, catalogDao.getRevision())
+    assertEquals(
+      listOf("Last known good"),
+      catalogDao.getTitlePage(null, "", 10).map { it.title },
+    )
+    val restored = userDao.getFolder(folderId)
+    assertEquals(scannedAt, restored?.lastScannedAt)
+    assertEquals("ready", restored?.lastScanStatus)
+    assertNull(restored?.lastScanError)
+  }
+
   @Test
   fun userMutationsAndVirtualQueueAreAtomicAndDurable() = runBlocking {
     val dao = user.userDao()

modules/astra-library-scanner/android/src/main/java/expo/modules/astralibraryscanner/AstraLibraryScannerModule.kt

@@ -41,6 +41,7 @@ import expo.modules.kotlin.records.Record
 import expo.modules.astralibraryscanner.data.AstraLibraryRepository
 import expo.modules.astralibraryscanner.data.LocalAudioFile
 import expo.modules.astralibraryscanner.data.LocalAudioMetadata
+import expo.modules.astralibraryscanner.data.ScanCancelledException
 import kotlinx.coroutines.CompletableDeferred
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.async
@@ -111,6 +112,11 @@ class AstraLibraryScannerModule : Module() {
   // decode can be cancelled too.
   private val activeAnalyses = ConcurrentHashMap<String, AtomicBoolean>()
 
+  // Scans are serialized by the repository, but register before acquiring that lock so
+  // cancelScan also stops a queued scan. A set keeps the native boundary robust if a
+  // caller ever bypasses the JS single-scan guard.
+  private val activeScans = ConcurrentHashMap.newKeySet<AtomicBoolean>()
+
   override fun definition() = ModuleDefinition {
     Name("AstraLibraryScanner")
 
@@ -134,49 +140,62 @@ class AstraLibraryScannerModule : Module() {
         mode: String,
         extensions: List<String>,
       ->
-      withContext(Dispatchers.IO) {
-        val repository = AstraLibraryRepository.get(requireContext())
-        repository.withUserRecovery { scanLocalFolder(
-          folderId = folderId.toLong(),
-          full = mode == "full",
-          discover = { treeUri ->
-            val listing = listAudioFiles(treeUri, extensions)
-            @Suppress("UNCHECKED_CAST")
-            val files = listing["files"] as? List<Map<String, Any?>> ?: emptyList()
-            @Suppress("UNCHECKED_CAST")
-            val covers = listing["covers"] as? Map<String, String> ?: emptyMap()
-            files.mapNotNull { file ->
-              val uri = file["uri"] as? String ?: return@mapNotNull null
-              val parentUri = file["parentUri"] as? String ?: ""
-              LocalAudioFile(
-                uri = uri,
-                name = file["name"] as? String ?: uri.substringAfterLast('/'),
-                size = (file["size"] as? Number)?.toLong(),
-                lastModified = (file["lastModified"] as? Number)?.toLong() ?: 0L,
-                mimeType = file["mimeType"] as? String,
-                parentUri = parentUri,
-                coverUri = covers[parentUri],
+      val cancelFlag = AtomicBoolean(false)
+      activeScans.add(cancelFlag)
+      try {
+        withContext(Dispatchers.IO) {
+          val repository = AstraLibraryRepository.get(requireContext())
+          repository.withUserRecovery { scanLocalFolder(
+            folderId = folderId.toLong(),
+            full = mode == "full",
+            discover = { treeUri ->
+              val listing = listAudioFiles(treeUri, extensions, cancelFlag)
+              @Suppress("UNCHECKED_CAST")
+              val files = listing["files"] as? List<Map<String, Any?>> ?: emptyList()
+              @Suppress("UNCHECKED_CAST")
+              val covers = listing["covers"] as? Map<String, String> ?: emptyMap()
+              files.mapNotNull { file ->
+                val uri = file["uri"] as? String ?: return@mapNotNull null
+                val parentUri = file["parentUri"] as? String ?: ""
+                LocalAudioFile(
+                  uri = uri,
+                  name = file["name"] as? String ?: uri.substringAfterLast('/'),
+                  size = (file["size"] as? Number)?.toLong(),
+                  lastModified = (file["lastModified"] as? Number)?.toLong() ?: 0L,
+                  mimeType = file["mimeType"] as? String,
+                  parentUri = parentUri,
+                  coverUri = covers[parentUri],
+                )
+              }
+            },
+            extract = { file ->
+              extractOne(file.uri, file.coverUri).toLocalAudioMetadata()
+            },
+            onProgress = { phase, processed, total, folderName ->
+              sendEvent(
+                "onScanProgress",
+                mapOf(
+                  "phase" to phase,
+                  "processed" to processed,
+                  "total" to total,
+                  "folderName" to folderName,
+                ),
               )
-            }
-          },
-          extract = { file ->
-            extractOne(file.uri, file.coverUri).toLocalAudioMetadata()
-          },
-          onProgress = { phase, processed, total, folderName ->
-            sendEvent(
-              "onScanProgress",
-              mapOf(
-                "phase" to phase,
-                "processed" to processed,
-                "total" to total,
-                "folderName" to folderName,
-              ),
-            )
-          },
-        ).toMap() }
+            },
+            isCancelled = cancelFlag::get,
+          ).toMap() }
+        }
+      } finally {
+        activeScans.remove(cancelFlag)
       }
     }
 
+    // Request cooperative cancellation for every active or queued library scan.
+    // Each scan unwinds at a safe checkpoint and discards its staging generation.
+    Function("cancelScan") {
+      activeScans.forEach { it.set(true) }
+    }
+
     // ONE whole-file PCM decode producing waveform peaks and (when withLoudness) gated
     // integrated loudness + sample peak. Both need every sample, so they ride the same
     // pass — running them separately meant decoding each track twice. Heavy, so cap
@@ -494,7 +513,11 @@ class AstraLibraryScannerModule : Module() {
   private val coverBaseNames = listOf("cover", "folder", "front", "albumart")
   private val coverExtensions = setOf("jpg", "jpeg", "png", "webp")
 
-  private fun listAudioFiles(treeUri: String, extensions: List<String>): Map<String, Any> {
+  private fun listAudioFiles(
+    treeUri: String,
+    extensions: List<String>,
+    cancelFlag: AtomicBoolean? = null,
+  ): Map<String, Any> {
     coverHashMemo.clear()
 
     val resolver = requireContext().contentResolver
@@ -517,6 +540,7 @@ class AstraLibraryScannerModule : Module() {
     queue.add(DocumentsContract.getTreeDocumentId(tree))
 
     while (queue.isNotEmpty()) {
+      if (cancelFlag?.get() == true) throw ScanCancelledException()
       val dirDocId = queue.removeFirst()
       val parentUri = DocumentsContract.buildDocumentUriUsingTree(tree, dirDocId).toString()
       val childrenUri = DocumentsContract.buildChildDocumentsUriUsingTree(tree, dirDocId)
@@ -525,6 +549,7 @@ class AstraLibraryScannerModule : Module() {
         ?: continue // directory disappeared mid-walk; skip it
       cursor.use {
         while (it.moveToNext()) {
+          if (cancelFlag?.get() == true) throw ScanCancelledException()
           val docId = it.getString(0) ?: continue
           val name = it.getString(1) ?: continue
           val mime = it.getString(2) ?: ""

modules/astra-library-scanner/android/src/main/java/expo/modules/astralibraryscanner/data/AstraLibraryRepository.kt

@@ -36,12 +36,17 @@ private const val MOBILE_SESSION_ID = "mobile"
 private const val ACTIVE_PLAYBACK_CONTEXT_ID = "active-context"
 
 class StaleRevisionException : IllegalStateException("STALE_REVISION")
+internal class ScanCancelledException : IllegalStateException("SCAN_CANCELLED")
 
 internal fun boundedPlaybackWindowStart(start: Long, total: Long): Long? {
   val normalized = start.coerceAtLeast(0)
   return normalized.takeIf { it < total }
 }
 
+private fun throwIfScanCancelled(isCancelled: () -> Boolean) {
+  if (isCancelled()) throw ScanCancelledException()
+}
+
 private data class RemoteSyncHandle(
   val syncId: String,
   val sourceKey: String,
@@ -355,6 +360,7 @@ class AstraLibraryRepository private constructor(
     discover: suspend (String) -> List<LocalAudioFile>,
     extract: suspend (LocalAudioFile) -> LocalAudioMetadata,
     onProgress: (phase: String, processed: Int, total: Int, folderName: String) -> Unit,
+    isCancelled: () -> Boolean = { false },
   ): NativeScanResult {
     initialize()
     return catalogWriterMutex.withLock {
@@ -387,8 +393,10 @@ class AstraLibraryRepository private constructor(
       updateOperationalStatus(LibraryStatus.SCANNING)
 
       try {
+        throwIfScanCancelled(isCancelled)
         onProgress("discovering", 0, 0, folder.displayName)
         val files = discover(folder.treeUri)
+        throwIfScanCancelled(isCancelled)
         onProgress("discovering", files.size, files.size, folder.displayName)
 
         val existing = dao.getActiveTrackEntitiesForSource(sourceKey)
@@ -401,9 +409,11 @@ class AstraLibraryRepository private constructor(
         var processed = 0
 
         for (batch in files.chunked(24)) {
+          throwIfScanCancelled(isCancelled)
           val rows = coroutineScope {
             batch.map { file ->
               async(Dispatchers.IO) {
+                throwIfScanCancelled(isCancelled)
                 val old = existingByPath[file.uri]
                 val unchanged = !full &&
                   old != null &&
@@ -422,6 +432,7 @@ class AstraLibraryRepository private constructor(
                   ) to false
                 } else {
                   val metadata = extract(file)
+                  throwIfScanCancelled(isCancelled)
                   if (!metadata.ok) {
                     if (old != null) {
                       old.copy(id = 0, generationId = generationId, sourceKey = sourceKey) to true
@@ -442,6 +453,7 @@ class AstraLibraryRepository private constructor(
               }
             }.awaitAll()
           }
+          throwIfScanCancelled(isCancelled)
           val insertRows = ArrayList<TrackEntity>(rows.size)
           for ((row, failed) in rows) {
             if (failed) errors += 1
@@ -454,6 +466,7 @@ class AstraLibraryRepository private constructor(
           onProgress("extracting", processed, files.size, folder.displayName)
         }
 
+        throwIfScanCancelled(isCancelled)
         val prospective = dao.getProspectiveTracks(sourceKey, generationId)
         val nextRevision = dao.getRevision() + 1
         onProgress("indexing", prospective.size, prospective.size, folder.displayName)
@@ -464,6 +477,9 @@ class AstraLibraryRepository private constructor(
             userDao.getFolders().associateBy(FolderEntity::id),
           )
         }
+        // Publishing is one Room transaction. Honour cancellation immediately before
+        // it starts; once inside, let it finish so the active catalog stays coherent.
+        throwIfScanCancelled(isCancelled)
         val revision = dao.publishGeneration(
           sourceKey = sourceKey,
           generationId = generationId,
@@ -488,6 +504,26 @@ class AstraLibraryRepository private constructor(
           total = files.size,
           revision = revision,
         )
+      } catch (_: ScanCancelledException) {
+        dao.deleteGenerationTracks(generationId)
+        dao.deleteGeneration(generationId)
+        userDao.updateFolderScanState(
+          folderId,
+          folder.lastScannedAt,
+          folder.lastScanStatus,
+          folder.lastScanError,
+        )
+        refreshReadyStatus()
+        scheduleSnapshot()
+        NativeScanResult(
+          added = 0,
+          updated = 0,
+          removed = 0,
+          errors = 0,
+          total = 0,
+          revision = dao.getRevision(),
+          cancelled = true,
+        )
       } catch (error: Throwable) {
         runCatching {
           dao.deleteGenerationTracks(generationId)

modules/astra-library-scanner/android/src/main/java/expo/modules/astralibraryscanner/data/CatalogReadModelBuilder.kt

@@ -57,6 +57,7 @@ data class NativeScanResult(
   val errors: Int,
   val total: Int,
   val revision: Long,
+  val cancelled: Boolean = false,
 ) {
   fun toMap(): Map<String, Any> = mapOf(
     "added" to added,
@@ -65,6 +66,7 @@ data class NativeScanResult(
     "errors" to errors,
     "total" to total,
     "catalogRevision" to revision.toString(),
+    "cancelled" to cancelled,
   )
 }
 

modules/astra-library-scanner/index.ts

@@ -87,6 +87,7 @@ export interface NativeScanResult {
   errors: number;
   total: number;
   catalogRevision: string;
+  cancelled: boolean;
 }
 
 /**
@@ -135,6 +136,8 @@ declare class AstraLibraryScannerModuleType extends NativeModule<AstraLibrarySca
     mode: 'incremental' | 'full',
     extensions: string[]
   ): Promise<NativeScanResult>;
+  /** Cooperatively stop every active or queued library scan at its next safe checkpoint. */
+  cancelScan(): void;
   /**
    * ONE whole-file PCM decode producing `bins` RMS waveform peaks and, when
    * `withLoudness`, gated integrated LUFS + sample peak. Both analyses need every

package.json

@@ -87,6 +87,7 @@
     "test:app-dialog": "node --experimental-strip-types --test src/components/dialogs/dialogQueue.test.mts",
     "test:home-greeting": "node --experimental-strip-types --test src/home/homeGreeting.test.mts",
     "test:session": "node --experimental-strip-types --test src/session/sessionState.test.mts src/session/playbackMaterialization.test.mts",
+    "test:library-scan": "node --experimental-strip-types --test src/library/scanCancellation.test.mts",
     "test:release-config": "node --experimental-strip-types --test plugins/withAstraAndroidRelease.test.mjs scripts/release/android-release.test.mjs src/release/buildInfo.test.mts",
     "test:release": "node scripts/run-release-tests.mjs",
     "release:validate": "node scripts/release/android-release.mjs validate github && node scripts/release/android-release.mjs validate google-play",

scripts/run-release-tests.mjs

@@ -23,6 +23,7 @@ const TEST_SCRIPTS = [
   'test:haptics',
   'test:home-greeting',
   'test:session',
+  'test:library-scan',
 ];
 
 for (const script of TEST_SCRIPTS) {

src/components/library/ScanProgress.tsx

@@ -1,6 +1,7 @@
-import { View } from 'react-native';
+import { Pressable, View } from 'react-native';
 import { Text } from '@/components/Text';
 import { spacing } from '@/theme';
+import { useRipple } from '@/theme/ripple';
 import { createThemedStyles, useColors } from '@/theme/themed';
 import { useLibraryStore } from '@/stores/libraryStore';
 
@@ -8,8 +9,11 @@ import { useLibraryStore } from '@/stores/libraryStore';
 export function ScanProgress() {
   const styles = useStyles();
   const colors = useColors();
+  const ripple = useRipple();
   const isScanning = useLibraryStore((s) => s.isScanning);
+  const isCancelling = useLibraryStore((s) => s.isCancelling);
   const progress = useLibraryStore((s) => s.scanProgress);
+  const cancelScan = useLibraryStore((s) => s.cancelScan);
 
   if (!isScanning) return null;
 
@@ -29,9 +33,33 @@ export function ScanProgress() {
 
   return (
     <View style={styles.container}>
-      <Text variant="caption" color={colors.textSecondary} numberOfLines={1}>
-        {label}
-      </Text>
+      <View style={styles.labelRow}>
+        <Text
+          variant="caption"
+          color={colors.textSecondary}
+          numberOfLines={1}
+          style={styles.label}
+        >
+          {label}
+        </Text>
+        <Pressable
+          android_ripple={ripple.bounded}
+          disabled={isCancelling}
+          onPress={cancelScan}
+          accessibilityRole="button"
+          accessibilityLabel={isCancelling ? 'Cancelling library scan' : 'Cancel library scan'}
+          accessibilityState={{ disabled: isCancelling, busy: isCancelling }}
+          hitSlop={6}
+          style={styles.cancelButton}
+        >
+          <Text
+            variant="caption"
+            color={isCancelling ? colors.textTertiary : colors.warning}
+          >
+            {isCancelling ? 'Cancelling…' : 'Cancel'}
+          </Text>
+        </Pressable>
+      </View>
       <View style={styles.track}>
         <View
           style={[
@@ -50,6 +78,20 @@ const useStyles = createThemedStyles((colors) => ({
     gap: spacing.xs,
     marginBottom: spacing.md,
   },
+  labelRow: {
+    minHeight: 32,
+    flexDirection: 'row',
+    alignItems: 'center',
+    gap: spacing.sm,
+  },
+  label: {
+    flex: 1,
+  },
+  cancelButton: {
+    minHeight: 32,
+    justifyContent: 'center',
+    paddingHorizontal: spacing.xs,
+  },
   track: {
     height: 2,
     backgroundColor: colors.glassBorder,

src/components/onboarding/OnboardingFlow.tsx

@@ -368,8 +368,11 @@ function StepHeader({
 function ScanBanner() {
   const styles = useStyles();
   const colors = useColors();
+  const ripple = useRipple();
   const isScanning = useLibraryStore((s) => s.isScanning);
+  const isCancelling = useLibraryStore((s) => s.isCancelling);
   const progress = useLibraryStore((s) => s.scanProgress);
+  const cancelScan = useLibraryStore((s) => s.cancelScan);
   if (!isScanning) return null;
   const detail =
     (progress.phase === 'extracting' || progress.phase === 'analyzing') && progress.total > 0
@@ -388,8 +391,27 @@ function ScanBanner() {
         numberOfLines={1}
         style={styles.scanBannerText}
       >
-        Scanning your library{detail ? ` · ${detail}` : '…'}
+        {isCancelling
+          ? 'Cancelling library scan…'
+          : `Scanning your library${detail ? ` · ${detail}` : '…'}`}
       </Text>
+      <Pressable
+        android_ripple={ripple.bounded}
+        disabled={isCancelling}
+        onPress={cancelScan}
+        accessibilityRole="button"
+        accessibilityLabel={isCancelling ? 'Cancelling library scan' : 'Cancel library scan'}
+        accessibilityState={{ disabled: isCancelling, busy: isCancelling }}
+        hitSlop={6}
+        style={styles.scanBannerCancel}
+      >
+        <Text
+          variant="caption"
+          color={isCancelling ? colors.textTertiary : colors.warning}
+        >
+          {isCancelling ? 'Cancelling…' : 'Cancel'}
+        </Text>
+      </Pressable>
     </Animated.View>
   );
 }
@@ -431,7 +453,12 @@ const useStyles = createThemedStyles((colors) => ({
     backgroundColor: colors.glassBg,
   },
   scanBannerText: {
-    maxWidth: 240,
+    flexShrink: 1,
+  },
+  scanBannerCancel: {
+    minHeight: 32,
+    justifyContent: 'center',
+    paddingHorizontal: spacing.xs,
   },
   scroll: {
     flex: 1,

src/library/scanCancellation.test.mts

@@ -0,0 +1,84 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+import {
+  createScanCancellationController,
+  runCancellableFolderScans,
+  type ScanResult,
+} from './scanCancellation.ts';
+
+const completed = (added: number): ScanResult => ({
+  added,
+  updated: 0,
+  removed: 0,
+  errors: 0,
+  cancelled: false,
+});
+
+test('cancellation controller is immediate and idempotent', () => {
+  const controller = createScanCancellationController();
+  assert.equal(controller.signal.cancelled, false);
+
+  controller.cancel();
+  controller.cancel();
+
+  assert.equal(controller.signal.cancelled, true);
+});
+
+test('cancelling between folders keeps completed results and starts no later folder', async () => {
+  const controller = createScanCancellationController();
+  const started: number[] = [];
+
+  const result = await runCancellableFolderScans(
+    [1, 2, 3],
+    controller.signal,
+    () => true,
+    async (folder) => {
+      started.push(folder);
+      if (folder === 1) controller.cancel();
+      return completed(folder);
+    }
+  );
+
+  assert.deepEqual(started, [1]);
+  assert.deepEqual(result, { ...completed(1), cancelled: true });
+});
+
+test('a native cancellation discards the active result but keeps earlier folders', async () => {
+  const started: number[] = [];
+
+  const result = await runCancellableFolderScans(
+    [1, 2, 3],
+    undefined,
+    () => true,
+    async (folder) => {
+      started.push(folder);
+      return folder === 2
+        ? { ...completed(0), cancelled: true }
+        : completed(folder);
+    }
+  );
+
+  assert.deepEqual(started, [1, 2]);
+  assert.deepEqual(result, { ...completed(1), cancelled: true });
+});
+
+test('unavailable folders are skipped without affecting totals', async () => {
+  const started: number[] = [];
+
+  const result = await runCancellableFolderScans(
+    [
+      { id: 1, available: true },
+      { id: 2, available: false },
+      { id: 3, available: true },
+    ],
+    undefined,
+    (folder) => folder.available,
+    async (folder) => {
+      started.push(folder.id);
+      return completed(folder.id);
+    }
+  );
+
+  assert.deepEqual(started, [1, 3]);
+  assert.deepEqual(result, completed(4));
+});

src/library/scanCancellation.ts

@@ -0,0 +1,60 @@
+export interface ScanResult {
+  added: number;
+  updated: number;
+  removed: number;
+  errors: number;
+  cancelled: boolean;
+}
+
+export interface ScanCancellationSignal {
+  readonly cancelled: boolean;
+}
+
+export interface ScanCancellationController {
+  readonly signal: ScanCancellationSignal;
+  cancel: () => void;
+}
+
+export function createScanCancellationController(): ScanCancellationController {
+  let cancelled = false;
+  return {
+    signal: {
+      get cancelled() {
+        return cancelled;
+      },
+    },
+    cancel: () => {
+      cancelled = true;
+    },
+  };
+}
+
+export async function runCancellableFolderScans<T>(
+  folders: readonly T[],
+  cancellation: ScanCancellationSignal | undefined,
+  isAvailable: (folder: T) => boolean,
+  scan: (folder: T) => Promise<ScanResult>
+): Promise<ScanResult> {
+  const total: ScanResult = {
+    added: 0,
+    updated: 0,
+    removed: 0,
+    errors: 0,
+    cancelled: false,
+  };
+
+  for (const folder of folders) {
+    if (!isAvailable(folder)) continue;
+    if (cancellation?.cancelled) return { ...total, cancelled: true };
+
+    const result = await scan(folder);
+    if (result.cancelled) return { ...total, cancelled: true };
+
+    total.added += result.added;
+    total.updated += result.updated;
+    total.removed += result.removed;
+    total.errors += result.errors;
+  }
+
+  return total;
+}

src/library/scanner.ts

@@ -6,6 +6,18 @@ import {
 } from '../../modules/astra-library-scanner';
 import type { LibraryFolder } from '@/types/library';
 import { AUDIO_EXTENSIONS } from './audioExtensions';
+import {
+  runCancellableFolderScans,
+  type ScanCancellationSignal,
+  type ScanResult,
+} from './scanCancellation';
+
+export {
+  createScanCancellationController,
+  type ScanCancellationController,
+  type ScanCancellationSignal,
+  type ScanResult,
+} from './scanCancellation';
 
 export interface ScanProgress {
   phase: 'discovering' | 'extracting' | 'analyzing';
@@ -18,13 +30,6 @@ export interface ScanCallbacks {
   onProgress?: (progress: ScanProgress) => void;
 }
 
-export interface ScanResult {
-  added: number;
-  updated: number;
-  removed: number;
-  errors: number;
-}
-
 type NativeFolder = LibraryFolder & {
   track_count: number;
   scan_status?: string;
@@ -44,29 +49,50 @@ function scanResult(result: NativeScanResult): ScanResult {
     updated: result.updated,
     removed: result.removed,
     errors: result.errors,
+    cancelled: result.cancelled === true,
   };
 }
 
+function cancelledScanResult(): ScanResult {
+  return { added: 0, updated: 0, removed: 0, errors: 0, cancelled: true };
+}
+
+export function cancelActiveScan(): void {
+  const scanner = AstraLibraryScanner as typeof AstraLibraryScanner & {
+    cancelScan?: () => void;
+  };
+  scanner.cancelScan?.();
+}
+
 export async function loadFolders(): Promise<NativeFolder[]> {
   await AstraLibraryData.initialize();
   return (await AstraLibraryData.listFolders()) as unknown as NativeFolder[];
 }
 
-export async function addFolderViaPicker(callbacks?: ScanCallbacks): Promise<ScanResult | null> {
+export async function addFolderViaPicker(
+  callbacks?: ScanCallbacks,
+  cancellation?: ScanCancellationSignal
+): Promise<ScanResult | null> {
   const permission = await StorageAccessFramework.requestDirectoryPermissionsAsync();
   if (!permission.granted) return null;
+  if (cancellation?.cancelled) return cancelledScanResult();
 
   const treeUri = permission.directoryUri;
   await AstraLibraryScanner.takePersistableUriPermission(treeUri);
   const folder = await AstraLibraryData.registerFolder(treeUri, displayNameFromTreeUri(treeUri));
-  return scanFolder(folder as unknown as LibraryFolder, { callbacks });
+  return scanFolder(folder as unknown as LibraryFolder, { callbacks, cancellation });
 }
 
 export async function scanFolder(
   folder: Omit<LibraryFolder, 'available'> & { available?: boolean },
-  opts: { mode?: 'incremental' | 'full'; callbacks?: ScanCallbacks } = {}
+  opts: {
+    mode?: 'incremental' | 'full';
+    callbacks?: ScanCallbacks;
+    cancellation?: ScanCancellationSignal;
+  } = {}
 ): Promise<ScanResult> {
-  const { mode = 'incremental', callbacks } = opts;
+  const { mode = 'incremental', callbacks, cancellation } = opts;
+  if (cancellation?.cancelled) return cancelledScanResult();
   const subscription = AstraLibraryScanner.addListener('onScanProgress', (event) => {
     const total = event.total ?? event.found ?? 0;
     callbacks?.onProgress?.({
@@ -78,26 +104,27 @@ export async function scanFolder(
   });
   try {
     const result = await AstraLibraryScanner.scanFolderNative(folder.id, mode, AUDIO_EXTENSIONS);
-    return scanResult(result);
+    const mapped = scanResult(result);
+    return cancellation?.cancelled ? { ...mapped, cancelled: true } : mapped;
   } finally {
     subscription.remove();
   }
 }
 
 export async function rescanAll(
-  opts: { mode?: 'incremental' | 'full'; callbacks?: ScanCallbacks } = {}
+  opts: {
+    mode?: 'incremental' | 'full';
+    callbacks?: ScanCallbacks;
+    cancellation?: ScanCancellationSignal;
+  } = {}
 ): Promise<ScanResult> {
   const folders = await loadFolders();
-  const total: ScanResult = { added: 0, updated: 0, removed: 0, errors: 0 };
-  for (const folder of folders) {
-    if (!folder.available) continue;
-    const result = await scanFolder(folder, opts);
-    total.added += result.added;
-    total.updated += result.updated;
-    total.removed += result.removed;
-    total.errors += result.errors;
-  }
-  return total;
+  return runCancellableFolderScans(
+    folders,
+    opts.cancellation,
+    (folder) => folder.available,
+    (folder) => scanFolder(folder, opts)
+  );
 }
 
 export async function removeFolder(folder: Pick<LibraryFolder, 'id'>): Promise<void> {

src/stores/libraryStore.ts

@@ -7,9 +7,12 @@ import {
 import type { Album, Artist, DbTrack, LibraryFolder } from '@/types/library';
 import {
   addFolderViaPicker,
+  cancelActiveScan,
+  createScanCancellationController,
   loadFolders,
   removeFolder as scannerRemoveFolder,
   rescanAll,
+  type ScanCancellationSignal,
   type ScanProgress,
   type ScanResult,
 } from '@/library/scanner';
@@ -79,6 +82,7 @@ interface LibraryStore {
   artistSort: ArtistSort;
   includeCollabArtists: boolean;
   isScanning: boolean;
+  isCancelling: boolean;
   scanProgress: ScanProgressState;
   scanError: string | null;
   trackNextCursor: string | null;
@@ -118,10 +122,12 @@ interface LibraryStore {
   removeFolder: (folderId: number) => Promise<void>;
   rescan: () => Promise<void>;
   rebuildLocalIndex: () => Promise<void>;
+  cancelScan: () => void;
 }
 
 let initPromise: Promise<void> | null = null;
 let nativeSubscriptionsInstalled = false;
+let activeScanCancellation: ReturnType<typeof createScanCancellationController> | null = null;
 
 // These grow without a cap on purpose. A sliding window that dropped items off the
 // head shrank the content height mid-scroll, which read as the list flinging itself
@@ -353,18 +359,30 @@ export const useLibraryStore = create<LibraryStore>((set, get) => {
     set({ sectionAnchors: anchors });
   };
 
-  const runScan = async (scan: () => Promise<ScanResult | null>) => {
+  const runScan = async (scan: (cancellation: ScanCancellationSignal) => Promise<ScanResult | null>) => {
     if (get().isScanning) return;
-    set({ isScanning: true, scanError: null, scanProgress: { ...IDLE_PROGRESS } });
+    const cancellation = createScanCancellationController();
+    activeScanCancellation = cancellation;
+    set({
+      isScanning: true,
+      isCancelling: false,
+      scanError: null,
+      scanProgress: { ...IDLE_PROGRESS },
+    });
     try {
-      await scan();
+      await scan(cancellation.signal);
     } catch (error) {
       set({ scanError: error instanceof Error ? error.message : String(error) });
     } finally {
       try {
         await get().refresh();
       } finally {
-        set({ isScanning: false, scanProgress: { ...IDLE_PROGRESS } });
+        if (activeScanCancellation === cancellation) activeScanCancellation = null;
+        set({
+          isScanning: false,
+          isCancelling: false,
+          scanProgress: { ...IDLE_PROGRESS },
+        });
         endScanService();
       }
     }
@@ -388,6 +406,7 @@ export const useLibraryStore = create<LibraryStore>((set, get) => {
     artistSort: 'name',
     includeCollabArtists: false,
     isScanning: false,
+    isCancelling: false,
     scanProgress: { ...IDLE_PROGRESS },
     scanError: null,
     trackNextCursor: null,
@@ -943,7 +962,8 @@ export const useLibraryStore = create<LibraryStore>((set, get) => {
       void resetSectionAnchors();
     },
 
-    addFolder: () => runScan(() => addFolderViaPicker({ onProgress })),
+    addFolder: () =>
+      runScan((cancellation) => addFolderViaPicker({ onProgress }, cancellation)),
 
     removeFolder: async (folderId) => {
       const folder = get().folders.find((entry) => entry.id === folderId);
@@ -952,8 +972,19 @@ export const useLibraryStore = create<LibraryStore>((set, get) => {
       await get().refresh();
     },
 
-    rescan: () => runScan(() => rescanAll({ callbacks: { onProgress } })),
+    rescan: () =>
+      runScan((cancellation) => rescanAll({ callbacks: { onProgress }, cancellation })),
 
-    rebuildLocalIndex: () => runScan(() => rescanAll({ mode: 'full', callbacks: { onProgress } })),
+    rebuildLocalIndex: () =>
+      runScan((cancellation) =>
+        rescanAll({ mode: 'full', callbacks: { onProgress }, cancellation })
+      ),
+
+    cancelScan: () => {
+      if (!get().isScanning || get().isCancelling || !activeScanCancellation) return;
+      set({ isCancelling: true });
+      activeScanCancellation.cancel();
+      cancelActiveScan();
+    },
   };
 });