feat: MCP app sampling support

[alexhancock]

Adds support for MCP apps to sample from the host's model connection, enabling Apps themselves to become AI-powered

See a more detailed proposal here: https://gist.github.com/alexhancock/2bb8b62500f33ccb29a0edb4aa7c5342

Motivation and Context

The idea is simply to let App code leverage the host's model connection, opening up a range of compelling app experiences (nested agents, specialized visual tutors, image generators, vision-based applications, etc)

How Has This Been Tested?

This concept has been implemented in goose (block/goose#7039) using the onFallbackRequest param, but this change elevates the idea to a first class citizen)

Breaking Changes

None

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

This MCP SEP is related as it adds the supported modalities concept to client capabilities as well modelcontextprotocol/modelcontextprotocol#2278. This way we can use the same type in modeling host capabilities re: sampling

[pkg-pr-new]

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@modelcontextprotocol/ext-apps

npm i https://pkg.pr.new/modelcontextprotocol/ext-apps/@modelcontextprotocol/ext-apps@477

@modelcontextprotocol/server-basic-react

npm i https://pkg.pr.new/modelcontextprotocol/ext-apps/@modelcontextprotocol/server-basic-react@477

@modelcontextprotocol/server-basic-vanillajs

npm i https://pkg.pr.new/modelcontextprotocol/ext-apps/@modelcontextprotocol/server-basic-vanillajs@477

@modelcontextprotocol/server-budget-allocator

npm i https://pkg.pr.new/modelcontextprotocol/ext-apps/@modelcontextprotocol/server-budget-allocator@477

@modelcontextprotocol/server-cohort-heatmap

npm i https://pkg.pr.new/modelcontextprotocol/ext-apps/@modelcontextprotocol/server-cohort-heatmap@477

@modelcontextprotocol/server-customer-segmentation

npm i https://pkg.pr.new/modelcontextprotocol/ext-apps/@modelcontextprotocol/server-customer-segmentation@477

@modelcontextprotocol/server-map

npm i https://pkg.pr.new/modelcontextprotocol/ext-apps/@modelcontextprotocol/server-map@477

@modelcontextprotocol/server-pdf

npm i https://pkg.pr.new/modelcontextprotocol/ext-apps/@modelcontextprotocol/server-pdf@477

@modelcontextprotocol/server-scenario-modeler

npm i https://pkg.pr.new/modelcontextprotocol/ext-apps/@modelcontextprotocol/server-scenario-modeler@477

@modelcontextprotocol/server-shadertoy

npm i https://pkg.pr.new/modelcontextprotocol/ext-apps/@modelcontextprotocol/server-shadertoy@477

@modelcontextprotocol/server-sheet-music

npm i https://pkg.pr.new/modelcontextprotocol/ext-apps/@modelcontextprotocol/server-sheet-music@477

@modelcontextprotocol/server-system-monitor

npm i https://pkg.pr.new/modelcontextprotocol/ext-apps/@modelcontextprotocol/server-system-monitor@477

@modelcontextprotocol/server-threejs

npm i https://pkg.pr.new/modelcontextprotocol/ext-apps/@modelcontextprotocol/server-threejs@477

@modelcontextprotocol/server-transcript

npm i https://pkg.pr.new/modelcontextprotocol/ext-apps/@modelcontextprotocol/server-transcript@477

@modelcontextprotocol/server-video-resource

npm i https://pkg.pr.new/modelcontextprotocol/ext-apps/@modelcontextprotocol/server-video-resource@477

@modelcontextprotocol/server-wiki-explorer

npm i https://pkg.pr.new/modelcontextprotocol/ext-apps/@modelcontextprotocol/server-wiki-explorer@477

commit: 430a8cd