fix: add SubtaskPart with metadata reference (anomalyco#10990)

Co-authored-by: yangtianzhe <yangtianzhe@corp.netease.com>

Author: YangTianz

packages/opencode/src/session/message-v2.ts

@@ -176,6 +176,8 @@ export namespace MessageV2 {
       })
       .optional(),
     command: z.string().optional(),
+  }).meta({
+    ref: "SubtaskPart",
   })
   export type SubtaskPart = z.infer<typeof SubtaskPart>