Improve local archive folder structure recognition.

app/src/main/java/org/thoughtcrime/securesms/backup/v2/local/ArchiveFileSystem.kt

@@ -104,11 +104,23 @@ class ArchiveFileSystem private constructor(private val context: Context, root:
     }
 
     /**
-     * Returns true if [dir] appears to be a SignalBackups directory based on its name and
-     * expected internal structure (presence of the "files" subdirectory).
+     * Returns true if [dir] appears to be a SignalBackups directory based on its expected internal
+     * structure. We can't rely on the directory being named [MAIN_DIRECTORY_NAME], since users may
+     * rename it or restore it into a differently-named folder (e.g. when transferring a backup
+     * between devices). A directory is therefore considered a backups directory if it either matches
+     * the expected name or directly contains the archive contents (a "files" subdirectory alongside
+     * at least one snapshot directory).
      */
     private fun looksLikeSignalBackupsDirectory(dir: DocumentFile): Boolean {
-      return dir.name == MAIN_DIRECTORY_NAME && dir.findFile("files") != null
+      if (dir.findFile("files") == null) {
+        return false
+      }
+
+      if (dir.name == MAIN_DIRECTORY_NAME) {
+        return true
+      }
+
+      return dir.listFiles().any { it.isDirectory && it.name?.startsWith(BACKUP_DIRECTORY_PREFIX) == true }
     }
 
     /**

app/src/test/java/org/thoughtcrime/securesms/backup/v2/local/ArchiveFileSystemTest.kt

@@ -98,6 +98,36 @@ class ArchiveFileSystemTest {
     assertThat(result).isNull()
   }
 
+  @Test
+  fun `openForRestore succeeds when the archive lives in a differently-named directory`() {
+    val renamed = temporaryFolder.newFolder("Signal")
+    buildArchiveContents(renamed)
+
+    val result = ArchiveFileSystem.openForRestore(context, DocumentFile.fromFile(renamed))
+
+    assertThat(result).isNotNull()
+  }
+
+  @Test
+  fun `openForRestore isRootedAtSignalBackups is true for a differently-named archive directory`() {
+    val renamed = temporaryFolder.newFolder("Signal")
+    buildArchiveContents(renamed)
+
+    val result = ArchiveFileSystem.openForRestore(context, DocumentFile.fromFile(renamed))!!
+
+    assertThat(result.isRootedAtSignalBackups).isTrue()
+  }
+
+  @Test
+  fun `openForRestore returns null for a differently-named directory that only contains a files folder`() {
+    val renamed = temporaryFolder.newFolder("Signal")
+    renamed.resolve("files").mkdir()
+
+    val result = ArchiveFileSystem.openForRestore(context, DocumentFile.fromFile(renamed))
+
+    assertThat(result).isNull()
+  }
+
   /**
    * Creates the SignalBackups directory structure inside [parent] and returns the SignalBackups directory.
    */
@@ -106,4 +136,12 @@ class ArchiveFileSystemTest {
     signalBackups.resolve("files").mkdir()
     return signalBackups
   }
+
+  /**
+   * Creates the raw archive contents (a "files" directory and a snapshot directory) directly inside [dir].
+   */
+  private fun buildArchiveContents(dir: java.io.File) {
+    dir.resolve("files").mkdir()
+    dir.resolve("${ArchiveFileSystem.BACKUP_DIRECTORY_PREFIX}-2026-01-01-00-00-00").mkdir()
+  }
 }