Replace client capability negotiation from extensions to experimental

[matteo8p]

Replace clientCapabilities?.extensions with clientCapabilities?.experimental. See #231

Motivation and Context

See #231

How Has This Been Tested?

This is just changing a .mdx doc

Breaking Changes

No

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

[pkg-pr-new]

Open in StackBlitz

@modelcontextprotocol/ext-apps

npm i https://pkg.pr.new/modelcontextprotocol/ext-apps/@modelcontextprotocol/ext-apps@232

@modelcontextprotocol/server-basic-react

npm i https://pkg.pr.new/modelcontextprotocol/ext-apps/@modelcontextprotocol/server-basic-react@232

@modelcontextprotocol/server-basic-vanillajs

npm i https://pkg.pr.new/modelcontextprotocol/ext-apps/@modelcontextprotocol/server-basic-vanillajs@232

@modelcontextprotocol/server-budget-allocator

npm i https://pkg.pr.new/modelcontextprotocol/ext-apps/@modelcontextprotocol/server-budget-allocator@232

@modelcontextprotocol/server-cohort-heatmap

npm i https://pkg.pr.new/modelcontextprotocol/ext-apps/@modelcontextprotocol/server-cohort-heatmap@232

@modelcontextprotocol/server-customer-segmentation

npm i https://pkg.pr.new/modelcontextprotocol/ext-apps/@modelcontextprotocol/server-customer-segmentation@232

@modelcontextprotocol/server-scenario-modeler

npm i https://pkg.pr.new/modelcontextprotocol/ext-apps/@modelcontextprotocol/server-scenario-modeler@232

@modelcontextprotocol/server-system-monitor

npm i https://pkg.pr.new/modelcontextprotocol/ext-apps/@modelcontextprotocol/server-system-monitor@232

@modelcontextprotocol/server-threejs

npm i https://pkg.pr.new/modelcontextprotocol/ext-apps/@modelcontextprotocol/server-threejs@232

@modelcontextprotocol/server-wiki-explorer

npm i https://pkg.pr.new/modelcontextprotocol/ext-apps/@modelcontextprotocol/server-wiki-explorer@232

commit: 3023c3c

[idosal]

See #231 (comment)