feat(android): implement private Rust storage runtime (#90)

tools/android-build/tests/mobile_contract.swift

@@ -61,6 +61,33 @@ enum MobileContractProbe {
         }
         let request = try validateMobileCredentialRequest(request: MobileCredentialRequest(requestId: "opaque", package: "de.example.app", signingCertificateSha256: String(repeating: "A", count: 64), origins: ["https://EXAMPLE.test:443/"]))
         precondition(request.origins == ["https://example.test"])
-        print("Swift native contract: fixtures/icons, callbacks, large payload, redaction, cancellation and concurrency passed")
+        do { try privateStorageProbe() }
+        catch MobilePrivateStorageFfiError.Failed(let kind) {
+            print("Swift private storage failed: \(kind)")
+            exit(1)
+        }
+        print("Swift native contract: fixtures/icons, callbacks, large payload, redaction, cancellation, concurrency and private storage passed")
     }
+    static func privateStorageProbe() throws {
+        let root = URL(fileURLWithPath: "/private/tmp").appendingPathComponent(UUID().uuidString)
+        defer { try? FileManager.default.removeItem(at: root) }
+        for name in ["files", "no-backup", "cache"] {
+            try FileManager.default.createDirectory(at: root.appendingPathComponent(name), withIntermediateDirectories: true)
+        }
+        let directories = MobilePrivateDirectories(
+            files: root.appendingPathComponent("files").path,
+            noBackup: root.appendingPathComponent("no-backup").path,
+            cache: root.appendingPathComponent("cache").path
+        )
+        precondition(!String(reflecting: directories).contains(root.path))
+        let storage = try openMobilePrivateRuntime(directories: directories)
+        precondition(storage.status().version == 1 && !storage.status().configured)
+        precondition(storage.shell().pages.first?.state == .empty)
+        precondition(!String(reflecting: storage.layout()).contains(root.path))
+        try storage.clearDisposableCache()
+        let recreated = try openMobilePrivateRuntime(directories: directories)
+        precondition(recreated.status() == storage.status())
+        precondition(recreated.layout() == storage.layout())
+    }
+
 }