`@ai-sdk/mcp`: support `structuredContent` / `outputSchema` for typed tool outputs

[mattrossman]

Description

MCP allows specifying outputSchema for tools to provide better type information. When specified, tools must populate structuredContent in their result as well as JSON encode structured data in .content text for backwards compatibility.

Currently, there's no way to leverage this type information with AI SDK's MCP client. I'd expect a way to read .structuredContent just as I'd read .content, but with type information from a defined outputSchema.

Spec:

• https://modelcontextprotocol.io/specification/2025-06-18/server/tools#structured-content
• https://modelcontextprotocol.io/specification/2025-06-18/server/tools#output-schema

MCPClient.tools() accepts a schemas option for type checking of tool inputs. Currently this only recognizes inputSchema to type tool inputs, while tool outputs are untyped.

• https://ai-sdk.dev/docs/reference/ai-sdk-core/create-mcp-client#tools.options.schemas

• https://ai-sdk.dev/docs/ai-sdk-core/mcp-tools#schema-definition

Comparatively, regular tool() definitions accept an outputSchema for typed outputs:

• https://ai-sdk.dev/docs/reference/ai-sdk-core/tool#tool.tool.output-schema

AI SDK Version

• @ai-sdk/mcp: 1.0.1

Code of Conduct

• I agree to follow this project's Code of Conduct

[lgrammel]

Identify issue type

Identified as Feature
Confidence: High

Rationale

This requests a new MCP client capability and API expansion rather than reporting a failure of currently documented behavior.

Evidence

• The MCP client currently recognizes only inputSchema in MCPClient.tools({ schemas }); tool outputs remain untyped.
• The request is to add MCP outputSchema support and expose typed structuredContent, analogous to regular tool() output schemas.