fix(agent): write absolute ProgramArguments path before SMAppService registration

SMAppService does not reliably resolve relative ProgramArguments paths
for launchd (launchd reports inferred program + partial import and
rejects spawn with EX_CONFIG). Rewrite the plist's ProgramArguments[0]
to the wrapper's absolute path just before register().

ShadowsocksX-NG2/App/LaunchAgentService.swift

@@ -9,9 +9,11 @@ protocol LaunchAgentControlling {
   func unregister() throws
 }
 
-/// 生产实现：plist 必须位于 app bundle `Contents/Library/LaunchAgents/`，
-/// ProgramArguments 为 Contents/ 相对路径（launchd 按注册 app 的 Contents/
-/// 解析）。
+/// 生产实现：注册时从 bundle 内模板 plist 生成带绝对 ProgramArguments 的
+/// 临时 plist，写入 `Contents/Library/LaunchAgents/` 后交给 SMAppService。
+/// SMAppService 对相对路径的 `ProgramArguments` 解析不可靠（launchd 显示
+/// `inferred program` + `partial import` 并以 EX_CONFIG 拒绝 spawn），
+/// 因此注册前把 wrapper 可执行文件的绝对路径写入 plist。
 struct SMAppLaunchAgentService: LaunchAgentControlling {
   static let plistName = "com.qiuyuzhou.ShadowsocksX-NG2.agent.plist"
 
@@ -33,10 +35,35 @@ struct SMAppLaunchAgentService: LaunchAgentControlling {
   }
 
   func register() throws {
+    try rewritePlistWithAbsoluteProgramPath()
     try service.register()
   }
 
   func unregister() throws {
     try service.unregister()
   }
+
+  /// 把 bundle 内 plist 的 ProgramArguments[0] 重写为 wrapper 的绝对路径。
+  /// 只在注册前调用；卸载不要求还原。
+  private func rewritePlistWithAbsoluteProgramPath() throws {
+    let bundle = Bundle.main.bundleURL
+    let plistURL = bundle.appendingPathComponent(
+      "Contents/Library/LaunchAgents/\(Self.plistName)")
+    let agentURL = bundle.appendingPathComponent("Contents/MacOS/ShadowsocksX-NG2Agent")
+    guard
+      let data = try? Data(contentsOf: plistURL),
+      var plist = try? PropertyListSerialization.propertyList(from: data, format: nil)
+        as? [String: Any]
+    else {
+      throw LaunchAgentPlistError.unreadable
+    }
+    plist["ProgramArguments"] = [agentURL.path]
+    let updated = try PropertyListSerialization.data(
+      fromPropertyList: plist, format: .xml, options: 0)
+    try updated.write(to: plistURL, options: .atomic)
+  }
+}
+
+enum LaunchAgentPlistError: Error, Equatable {
+  case unreadable
 }