test: 新增三级继承用例（三层全标 @SerializerParent）

- threeLevelAllMacro：爷/父/子 每层字段都导出、反序列化全部回填
- threeLevelFieldSeparation：三层字段互不遮蔽、互不覆盖
- 新增模型 GrandAll → MidAll → LeafAll（每层标宏）
- 18 用例全绿

src/tests/JsonSerializer_test.cj

@@ -70,6 +70,22 @@ class LeafChild <: MidParent {
     public init() {}
 }
 
+// 三级继承（全标宏）：爷 → 父 → 子 每层都标注 @SerializerParent
+@SerializerParent
+open class GrandAll {
+    public var _ga: String = ""
+}
+
+@SerializerParent
+open class MidAll <: GrandAll {
+    public var _ma: String = ""
+}
+
+class LeafAll <: MidAll {
+    public var _la: String = ""
+    public init() {}
+}
+
 func makeUser(): User {
     let u = User()
     u._id = "u-1"
@@ -374,4 +390,44 @@ public class JsonSerializerTests {
         let json = JsonSerializer.Serialize(leaf)
         @Expect(json.contains("\"_gp\": \"auto\""), true)
     }
+
+    /// 三级继承（全标宏）：爷/父/子 每层字段都导出、反序列化全部回填
+    @TestCase
+    public func threeLevelAllMacro() {
+        let leaf = LeafAll()
+        leaf._ga = "ga-v"
+        leaf._ma = "ma-v"
+        leaf._la = "la-v"
+
+        let json = JsonSerializer.Serialize(leaf)
+        @Expect(json.contains("\"_ga\": \"ga-v\""), true)  // 爷字段（宏）导出
+        @Expect(json.contains("\"_ma\": \"ma-v\""), true)  // 父字段（宏）导出
+        @Expect(json.contains("\"_la\": \"la-v\""), true)  // 子字段（反射）导出
+
+        let back = JsonSerializer.Deserialize<LeafAll>(json)
+        @Expect(back._ga, "ga-v")
+        @Expect(back._ma, "ma-v")
+        @Expect(back._la, "la-v")
+    }
+
+    /// 三级继承：每层字段互不遮蔽（字段名不同），导出顺序无关，值各自正确
+    @TestCase
+    public func threeLevelFieldSeparation() {
+        let leaf = LeafAll()
+        leaf._ga = "G"
+        leaf._ma = "M"
+        leaf._la = "L"
+        let json = JsonSerializer.Serialize(leaf)
+
+        // 三个字段值互不串
+        @Expect(json.contains("\"_ga\": \"G\""), true)
+        @Expect(json.contains("\"_ma\": \"M\""), true)
+        @Expect(json.contains("\"_la\": \"L\""), true)
+
+        // 反序列化后互不覆盖
+        let back = JsonSerializer.Deserialize<LeafAll>(json)
+        @Expect(back._ga, "G")
+        @Expect(back._ma, "M")
+        @Expect(back._la, "L")
+    }
 }