fix(dify): handle string query response

[guslegend0510]

AgentScope-Java Version

2.0.0-SNAPSHOT

Description

Background

The Dify RAG integration fails against real Dify Cloud (api.dify.ai) responses because the top-level query field is returned as a JSON string, while DifyResponse.Query only supported the object form. This caused DifyResponse deserialization to fail and made kb_search results/references empty.

Purpose

Make the Dify response model compatible with both query: "..." and query: { "content": "..." } payloads so retrieval works reliably with real Dify Cloud deployments.

Changes

• Add a delegating Jackson creator to DifyResponse.Query so string payloads can be deserialized.
• Keep the existing bean-style object mapping so both response shapes remain supported.
• Add regression tests for both string and object query payloads.

How to test

• mvn -pl agentscope-extensions/agentscope-extensions-rag/agentscope-extensions-rag-dify -am -Dtest=DifyRAGClientTest test

Related issue

• Fixes [Bug] Dify Cloud 检索接口 query 字段返回字符串，导致 DifyResponse 反序列化失败（kb_search 对 api.dify.ai 引用恒为空） #1917

[itxaiohanglover]

Clean fix — using @JsonCreator with DELEGATING mode is the right approach here, and I like that you kept the object form working too. Test coverage for both string and object query formats is great. Looks good to me.