[ydflow]

Fixes #3388

PR Title Format

fix(tool): keep an MCP structured tool result

AgentScope Version

2.0.11dev (base: main @ 58da57a)

Description

An MCP tool that declares an outputSchema may return its payload only in
CallToolResult.structuredContent. MCPTool.call() converted
CallToolResult.content only, so such a call produced a ToolChunk with no
blocks: the next request carried an empty tool result (content: "" for
OpenAI, {"output": ""} for Gemini, (empty tool output) for Anthropic) and
the model lost the result entirely, without any log line.

Change (src/agentscope/tool/_adapters.py): after converting
result.content, append json.dumps(result.structured_content, ensure_ascii=False) as a TextBlock when the converted content contains no
text block.

• Empty content + structuredContent → the JSON is the tool result.
• Media-only content + structuredContent → image block keeps its JSON
  companion (a text block cannot carry it, so the spec's
  backwards-compatibility workaround is not even possible here).
• isError results keep their state and also carry the payload.
• Server already serialized the JSON into a text block → unchanged, no
  duplicated payload.
• No structuredContent → unchanged.

The stateful (session) and stateless (client_gen) paths both go through
call(), so both are covered by the single change.

Tests: new tests/mcp_tool_result_test.py (5 cases, fake session, no
network or server process needed). Before the change the three payload cases
fail (0 != 1); after the change all 5 pass. Existing MCP suite still passes:
tests/mcp_client_reconnect_test.py, tests/mcp_sse_client_test.py,
tests/mcp_streamable_http_client_test.py → 11 passed.

Checks: black --line-length=79, flake8 --extend-ignore=E203,
pylint (10.00/10 with the repo's disable list), mypy (repo args) all clean
on the two touched files.

Note on overlap: my open #3372 also edits src/agentscope/tool/_adapters.py,
but in the name-composition hunk (~line 240); this change is in MCPTool.call
(~line 350). They are independent and merge in either order.

Out of scope here (same conversion function, reported in #3388):
ResourceLink and BlobResourceContents are still dropped.

Checklist

• An issue has been created for this PR
• I have read the CONTRIBUTING.md
• Docstrings are in Google style
• Related documentation has been updated (e.g. links, examples, etc.) in documentation repository — not applicable, behaviour of an existing API only
• Code is ready for review

[qbc2016]

LGTM

[ChaoDiDiaoAA]

I'm working on a focused follow-up to #3389 for mixed MCP results. On main 26ec620b, an ordinary or empty TextContent still suppresses structuredContent, so fields present only in the structured payload never reach the model.

The local fix preserves existing content and appends JSON unless an identical serialized text block already carries it. Regression tests cover summaries, empty text, error details, empty objects, duplicate JSON, and the real Toolkit-to-OpenAI-formatter path. They reproduced the loss before the fix and now pass locally.

This scope excludes ResourceLink/blob support in #2799 and connection cleanup in #3402. Differently formatted equivalent JSON may still be duplicated; feedback on that compatibility tradeoff is welcome.