refactor(runtime): 收据写者归一为 Agent wrapper

RuntimeFileStore.writeRuntimeReceipt 生产零调用（17 处调用全为测试夹具），
从生产 interface 删除；测试侧经 RuntimeReceiptFixture 的 extension 以同签名
承接，调用点零改动。收据格式知识仍由 RuntimeDeploymentReceipt 类型承载，
GUI 侧只保留 readRuntimeReceipt 读缝。

评审候选⑥ 6a：wrapper 是唯一收据写者，GUI 永不伪造收据。

ShadowsocksX-NG2/Domain/RuntimeFileStore.swift

@@ -156,25 +156,13 @@ struct RuntimeFileStore {
     try? Data(contentsOf: fileURL)
   }
 
+  /// 部署收据只读：唯一生产写者是 Agent wrapper（AgentContract.writeRuntimeReceipt），
+  /// GUI 在健康检查中核对 pid 与契约摘要，从不写。
   func readRuntimeReceipt() -> RuntimeDeploymentReceipt? {
     guard let data = try? Data(contentsOf: runtimeStatusFileURL) else { return nil }
     return try? JSONDecoder().decode(RuntimeDeploymentReceipt.self, from: data)
   }
 
-  func writeRuntimeReceipt(for document: SslocalRuntimeDocument, processID: Int32) throws {
-    guard let digest = document.deploymentSHA256 else {
-      throw PersistenceError.ioFailure(detail: "Runtime contract digest is unavailable")
-    }
-    let receipt = RuntimeDeploymentReceipt(processID: processID, contractSHA256: digest)
-    let encoder = JSONEncoder()
-    encoder.outputFormatting = [.sortedKeys]
-    do {
-      try AtomicFileWriter.write(try encoder.encode(receipt), to: runtimeStatusFileURL)
-    } catch {
-      throw PersistenceError.ioFailure(detail: String(describing: error))
-    }
-  }
-
   /// 显式停止清理（D2 停止协议末端）：运行时契约、wrapper pid、ACL 链接与
   /// 变体、digest 清单及原子写残留。异常崩溃路径不调用本方法（文件保留供
   /// KeepAlive 重放，D5）。文件缺失时调用无害。

ShadowsocksX-NG2/Tests/RuntimeReceiptFixture.swift

@@ -0,0 +1,23 @@
+import Foundation
+
+@testable import ShadowsocksX_NG2
+
+/// 测试支持：模拟 wrapper 写入部署收据。生产唯一收据写者是 Agent wrapper
+/// （AgentContract.writeRuntimeReceipt），GUI 侧只有读（readRuntimeReceipt）；
+/// 收据格式知识由 Domain 的 RuntimeDeploymentReceipt 类型承载，此处只复刻
+/// wrapper 的「写动作」供夹具布置磁盘状态。
+extension RuntimeFileStore {
+  func writeRuntimeReceipt(for document: SslocalRuntimeDocument, processID: Int32) throws {
+    guard let digest = document.deploymentSHA256 else {
+      throw PersistenceError.ioFailure(detail: "Runtime contract digest is unavailable")
+    }
+    let receipt = RuntimeDeploymentReceipt(processID: processID, contractSHA256: digest)
+    let encoder = JSONEncoder()
+    encoder.outputFormatting = [.sortedKeys]
+    do {
+      try AtomicFileWriter.write(try encoder.encode(receipt), to: runtimeStatusFileURL)
+    } catch {
+      throw PersistenceError.ioFailure(detail: String(describing: error))
+    }
+  }
+}