Add global search backfill worker (#7860)

* Add search backfill worker

This will run on background at most once an hour while the device has internet connectivity and the device is charging and start back-paginating through the user's rooms to make sure the search results are populated.

It'll run for the maximum time the default workers allow, 10 minutes.

* Create `RustMatrixClient.Factory` AssistedFactory to help with DI and add `SearchBackfillService`

* Start search backfill when entering the search screen, just once. This should help getting initial search results if none or few are found at first

libraries/matrix/test/src/main/kotlin/io/element/android/libraries/matrix/test/FakeMatrixClient.kt

@@ -40,6 +40,7 @@ import io.element.android.libraries.matrix.api.roomdirectory.RoomDirectoryServic
 import io.element.android.libraries.matrix.api.roomlist.RoomListService
 import io.element.android.libraries.matrix.api.scanner.ContentScanner
 import io.element.android.libraries.matrix.api.search.MessageSearchService
+import io.element.android.libraries.matrix.api.search.SearchBackfillService
 import io.element.android.libraries.matrix.api.spaces.SpaceService
 import io.element.android.libraries.matrix.api.sync.SlidingSyncVersion
 import io.element.android.libraries.matrix.api.sync.SyncService
@@ -57,6 +58,7 @@ import io.element.android.libraries.matrix.test.pushers.FakePushersService
 import io.element.android.libraries.matrix.test.roomdirectory.FakeRoomDirectoryService
 import io.element.android.libraries.matrix.test.roomlist.FakeRoomListService
 import io.element.android.libraries.matrix.test.search.FakeMessageSearchService
+import io.element.android.libraries.matrix.test.search.FakeSearchBackfillService
 import io.element.android.libraries.matrix.test.spaces.FakeSpaceService
 import io.element.android.libraries.matrix.test.sync.FakeSyncService
 import io.element.android.libraries.matrix.test.verification.FakeSessionVerificationService
@@ -131,6 +133,7 @@ class FakeMatrixClient(
     private val markRoomAsFullyReadResult: (RoomId, EventId) -> Result<Unit> = { _, _ -> lambdaError() },
     private val markAllRoomsAsReadResult: () -> Result<Unit> = { Result.success(Unit) },
     private val performDatabaseVacuumLambda: () -> Result<Unit> = { lambdaError() },
+    override val searchBackfillService: SearchBackfillService = FakeSearchBackfillService(),
     private val getDatabaseSizesLambda: () -> Result<SdkStoreSizes> = { lambdaError() },
     private val resetWellKnownConfigLambda: () -> Result<Unit> = { lambdaError() },
     private val enableAutomaticCallStatusLambda: (Boolean) -> Unit = { },

libraries/matrix/test/src/main/kotlin/io/element/android/libraries/matrix/test/FakeSdkPendingTask.kt

@@ -0,0 +1,20 @@
+/*
+ * Copyright (c) 2026 Element Creations Ltd.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial.
+ * Please see LICENSE files in the repository root for full details.
+ */
+
+package io.element.android.libraries.matrix.test
+
+import io.element.android.libraries.matrix.api.SdkPendingTask
+import io.element.android.tests.testutils.lambda.lambdaError
+
+class FakeSdkPendingTask(
+    private val isRunningLambda: () -> Boolean = { lambdaError() },
+    private val closeLambda: () -> Unit = { lambdaError() },
+) : SdkPendingTask {
+    override fun isRunning(): Boolean = isRunningLambda()
+
+    override fun close() = closeLambda()
+}

libraries/matrix/test/src/main/kotlin/io/element/android/libraries/matrix/test/search/FakeSearchBackfillService.kt

@@ -0,0 +1,41 @@
+/*
+ * Copyright (c) 2026 Element Creations Ltd.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial.
+ * Please see LICENSE files in the repository root for full details.
+ */
+
+package io.element.android.libraries.matrix.test.search
+
+import io.element.android.libraries.matrix.api.SdkPendingTask
+import io.element.android.libraries.matrix.api.search.SearchBackfillService
+import io.element.android.libraries.matrix.api.search.SearchBackfillStrategy
+import io.element.android.tests.testutils.lambda.lambdaError
+
+class FakeSearchBackfillService(
+    private val schedulePeriodicSearchBackfillLambda: (SearchBackfillStrategy) -> Result<Unit> = { lambdaError() },
+    private val cancelPeriodicSearchBackfillLambda: () -> Unit = { lambdaError() },
+    private val startSearchBackfillLambda: (SearchBackfillStrategy) -> Result<SdkPendingTask> = { lambdaError() },
+    private val isSearchBackfillRunningLambda: () -> Boolean = { false },
+    private val cancelSearchBackfillLambda: () -> Result<Unit> = { lambdaError() },
+) : SearchBackfillService {
+    override suspend fun schedulePeriodicSearchBackfill(strategy: SearchBackfillStrategy): Result<Unit> {
+        return schedulePeriodicSearchBackfillLambda(strategy)
+    }
+
+    override fun cancelPeriodicSearchBackfill() {
+        cancelPeriodicSearchBackfillLambda()
+    }
+
+    override fun startSearchBackfill(strategy: SearchBackfillStrategy): Result<SdkPendingTask> {
+        return startSearchBackfillLambda(strategy)
+    }
+
+    override fun isSearchBackfillRunning(): Boolean {
+        return isSearchBackfillRunningLambda()
+    }
+
+    override fun cancelSearchBackfill(): Result<Unit> {
+        return cancelSearchBackfillLambda()
+    }
+}