fix: preserve structured SDK MCP tool results

[anthony-maio]

Summary

• preserve structured resource and resource_link MCP content blocks in create_sdk_mcp_server() instead of flattening them into text
• preserve those structured blocks again when the SDK MCP JSON-RPC bridge serializes tools/call results back to the CLI
• update the SDK MCP integration tests to assert structured resources round-trip end-to-end

Problem

SDK MCP tool handlers can return structured resource blocks, but the Python SDK currently flattens them to plain text in two places:

1. create_sdk_mcp_server() converts resource and resource_link outputs into TextContent
2. _handle_sdk_mcp_request() converts those MCP content objects back into text again

That strips MIME type, URI, and resource structure, which prevents JSON payloads like application/json from surviving the SDK bridge.

Test Plan

• python -m pytest tests/test_sdk_mcp_integration.py
• python -m ruff check src/claude_agent_sdk/__init__.py src/claude_agent_sdk/_internal/query.py tests/test_sdk_mcp_integration.py
• python -m mypy src/

Fixes #695

[Copilot]

Pull request overview

This PR fixes SDK MCP tool result handling so structured MCP resource and resource_link content blocks round-trip through the Python SDK bridge without being flattened into text, enabling preservation of URI/MIME metadata and structured payloads (e.g., JSON).

Changes:

• Preserve resource_link and resource blocks in create_sdk_mcp_server() by emitting MCP ResourceLink / EmbeddedResource objects instead of TextContent.
• Preserve structured MCP content blocks when serializing tools/call results back through the JSON-RPC bridge (Query._handle_sdk_mcp_request()).
• Update/extend integration tests to assert end-to-end structured resource round-tripping (including blob resources).

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
tests/test_sdk_mcp_integration.py	Adds/updates integration tests to assert structured resource / resource_link blocks are preserved through server + JSON-RPC bridge.
src/claude_agent_sdk/_internal/query.py	Updates JSON-RPC bridge serialization to emit structured MCP content via model_dump() for resources/links (and audio).
src/claude_agent_sdk/init.py	Updates SDK MCP server tool result conversion to construct structured ResourceLink and EmbeddedResource (text/blob) blocks.

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