fix(opencode): retry on xfyun engine busy response

When xfyun (讯飞云) returns 'engine busy', OpenCode should retry instead of failing.

Fixes #31812

Author: zhangmq45

packages/opencode/src/session/retry.ts

@@ -129,7 +129,8 @@ export function retryable(error: Err, provider: string) {
     if (
       lower.includes("rate increased too quickly") ||
       lower.includes("rate limit") ||
-      lower.includes("too many requests")
+      lower.includes("too many requests") ||
+      lower.includes("engine busy")
     ) {
       return { message: msg }
     }