Add first MCP server sample in C# and .NET

[balajibashyam]

Summary

Adds a verified .NET 10 companion sample for the
Build Your First MCP Server in C# and .NET tutorial.

What's included

• New sample: dotnet-ai/mcp-server-csharp-dotnet/

  • ModelContextProtocol 2.2.0
  • stdio MCP server/client
  • exactly three read-only tools
  • dependency-injected deterministic JSON-backed stores
  • real MCP tool discovery and invocation
  • protocol-level unknown-tool rejection
  • McpClientTool -> AIFunction compatibility check
  • architecture and verification documentation
  • 13 deterministic tests

• Root README

  • new sample row
  • run commands
  • corrected .NET AI repository-tree subsection with the MCP sample added

• GitHub Actions

  • new test-mcp-server-csharp-dotnet job
  • sample path added to push and pull-request filters
  • deterministic restore/build/test/MCP stdio E2E only
  • no LLM or provider secret

Versions

• Target framework: net10.0
• SDK baseline: 10.0.401
• ModelContextProtocol: 2.2.0
• Microsoft.Extensions.Hosting: 10.0.12
• xunit.v3.mtp-v2: 4.0.1

Local validation

• Release build — PASS, 0 warnings / 0 errors
• deterministic tests — PASS, 13/13
• MCP stdio E2E — PASS
• tool discovery — PASS, exactly 3
• all three tool calls — PASS
• unknown-tool rejection — PASS
• targeted credential/private-path scan — clean
• generated artifacts excluded from staging

Deliberately omitted

• Agent Framework
• LLM-driven tool selection
• Streamable HTTP / remote MCP hosting
• OAuth/authentication/authorization
• MCP resources, prompts, sampling, elicitation, and tasks
• write-capable/destructive tools
• databases
• RAG/vector search
• multi-agent workflows
• Docker/Kubernetes/cloud deployment
• production-readiness claims