test: lock bind/setPlayMode JSON encoding via semantic assertions

Replace brittle exact-byte equality checks in BindPayloadByteRegressionTests
with substring + dict-based semantic assertions that tolerate Swift JSONEncoder
key-order variance across runtime versions.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Tests/DuooomiBleSDKTests/PlayModeTests.swift

@@ -103,3 +103,47 @@ final class SetPlayModeGuardTests: XCTestCase {
         wait(for: [exp], timeout: 1.0)
     }
 }
+
+final class BindPayloadByteRegressionTests: XCTestCase {
+    /// 关键回归：bind / unbind 在 loop=nil 时报文必须完全不含 "loop" key —— 不能输出 "loop":null。
+    /// 不假设 JSONEncoder key 顺序（Swift 不同版本顺序可能不同），用 substring + dict 断言锁语义。
+    func testBindPayloadNilLoopOmitsKeyAndNull() throws {
+        let payload = BindPayload(type: 0x0F, userId: "abc", loop: nil)
+        let data = try JSONEncoder().encode(payload)
+        let json = String(data: data, encoding: .utf8) ?? ""
+        // 字面层：JSON 文本不允许出现 "loop" 或 "null"
+        XCTAssertFalse(json.contains("loop"), "loop key MUST be absent; got \(json)")
+        XCTAssertFalse(json.contains("null"), "null literal MUST be absent; got \(json)")
+        // 结构层：反序列化后只有 type / userId，无第三个 key
+        let dict = try JSONSerialization.jsonObject(with: data) as? [String: Any] ?? [:]
+        XCTAssertEqual(dict.count, 2)
+        XCTAssertEqual(dict["type"] as? Int, 15)
+        XCTAssertEqual(dict["userId"] as? String, "abc")
+        XCTAssertNil(dict["loop"])
+    }
+
+    /// setPlayMode 报文：loop=1 必须以整数形式出现（不是 "1" 字符串）。
+    func testSetPlayModePayloadIncludesLoopOne() throws {
+        let payload = BindPayload(type: 0x0F, userId: "abc", loop: 1)
+        let data = try JSONEncoder().encode(payload)
+        let json = String(data: data, encoding: .utf8) ?? ""
+        // 字面层子串：必须出现 "loop":1（数字，无引号）
+        XCTAssertTrue(json.contains(#""loop":1"#), "expected literal substring \"loop\":1 in \(json)")
+        // 结构层
+        let dict = try JSONSerialization.jsonObject(with: data) as? [String: Any] ?? [:]
+        XCTAssertEqual(dict.count, 3)
+        XCTAssertEqual(dict["type"] as? Int, 15)
+        XCTAssertEqual(dict["userId"] as? String, "abc")
+        XCTAssertEqual(dict["loop"] as? Int, 1)
+    }
+
+    /// setPlayMode 报文：loop=0 边界情况，必须以整数 0 出现（不是被当作 "default" 省略）。
+    func testSetPlayModePayloadIncludesLoopZero() throws {
+        let payload = BindPayload(type: 0x0F, userId: "abc", loop: 0)
+        let data = try JSONEncoder().encode(payload)
+        let json = String(data: data, encoding: .utf8) ?? ""
+        XCTAssertTrue(json.contains(#""loop":0"#), "expected literal substring \"loop\":0 in \(json)")
+        let dict = try JSONSerialization.jsonObject(with: data) as? [String: Any] ?? [:]
+        XCTAssertEqual(dict["loop"] as? Int, 0)
+    }
+}