added .read state

Tests/ChatMessageDeliveryTests.swift

@@ -0,0 +1,38 @@
+import XCTest
+@testable import Luma
+
+final class ChatMessageDeliveryTests: XCTestCase {
+    func testMergeKeepsTheStrongestState() {
+        XCTAssertEqual(ChatMessage.Delivery.sent.merged(with: .sending), .sent)
+        XCTAssertEqual(ChatMessage.Delivery.sending.merged(with: .sent), .sent)
+        XCTAssertEqual(ChatMessage.Delivery.sent.merged(with: .delivered), .delivered)
+        XCTAssertEqual(ChatMessage.Delivery.delivered.merged(with: .read), .read)
+        XCTAssertEqual(ChatMessage.Delivery.read.merged(with: .sent), .read)
+        XCTAssertEqual(ChatMessage.Delivery.read.merged(with: .delivered), .read)
+    }
+
+    func testMAMReplayNeverDowngradesReadState() {
+        // The archived copy of an outgoing message carries `.sent`; the local
+        // copy that received the peer's displayed marker must stay `.read`.
+        XCTAssertEqual(ChatMessage.Delivery.read.merged(with: .sent), .read)
+        XCTAssertEqual(ChatMessage.Delivery.delivered.merged(with: .sent), .delivered)
+    }
+
+    func testFailedIsSticky() {
+        XCTAssertEqual(ChatMessage.Delivery.failed.merged(with: .sent), .failed)
+        XCTAssertEqual(ChatMessage.Delivery.sent.merged(with: .failed), .failed)
+    }
+
+    func testReadMessagesRemainEditableAndRetractable() {
+        let message = ChatMessage(
+            conversationID: "bob@example.org",
+            senderJID: "alice@example.org",
+            body: "привет",
+            direction: .outgoing,
+            delivery: .read,
+            security: .plaintext
+        )
+        XCTAssertTrue(message.canBeEdited)
+        XCTAssertTrue(message.canBeRetracted)
+    }
+}