Add file-based MCP server sample for .NET 10 (#3) (#931)

samples/FileBasedMcpServer/README.md

@@ -0,0 +1,64 @@
+# File-Based MCP Server Sample
+
+This sample demonstrates how to create a complete MCP (Model Context Protocol) server using .NET 10's file-based programs feature. Unlike traditional .NET projects that require a `.csproj` file, file-based programs allow you to write and run complete applications in a single `.cs` file.
+
+## Requirements
+
+- .NET 10 SDK (RC2 or later)
+- No project file required!
+
+## Running the Sample
+
+Simply run the Program.cs file directly:
+
+```bash
+dotnet run Program.cs
+```
+
+The server will start and listen for MCP messages on stdin/stdout (stdio transport).
+
+### Making it Executable (Unix/Linux/macOS)
+
+On Unix-like systems, you can make the file executable:
+
+```bash
+chmod +x Program.cs
+./Program.cs
+```
+
+Note: The shebang line uses `/usr/bin/env` to locate `dotnet`, so ensure it's in your PATH.
+
+## Testing the Server
+
+You can test the server by using `@modelcontextprotocol/inspector`, any stdio-compatible client, or sending JSON-RPC messages to stdin. Here's an example:
+
+### Initialize the server:
+```bash
+echo '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2024-11-05","capabilities":{},"clientInfo":{"name":"test-client","version":"1.0"}}}' | dotnet run Program.cs
+```
+
+### List available tools:
+```bash
+(
+  echo '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2024-11-05","capabilities":{},"clientInfo":{"name":"test-client","version":"1.0"}}}'
+  sleep 0.5
+  echo '{"jsonrpc":"2.0","id":2,"method":"tools/list","params":{}}'
+  sleep 1
+) | dotnet run Program.cs 2>/dev/null | grep '^{' | jq .
+```
+
+### Call the echo tool:
+```bash
+(
+  echo '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2024-11-05","capabilities":{},"clientInfo":{"name":"test-client","version":"1.0"}}}'
+  sleep 0.5
+  echo '{"jsonrpc":"2.0","id":2,"method":"tools/call","params":{"name":"echo","arguments":{"message":"Hello, MCP!"}}}'
+  sleep 1
+) | dotnet run Program.cs 2>/dev/null | grep '^{' | jq .
+```
+
+## Reference
+
+- [File-Based Programs Tutorial](https://learn.microsoft.com/en-us/dotnet/csharp/fundamentals/tutorials/file-based-programs)
+- [C# Preprocessor Directives for File-Based Apps](https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/preprocessor-directives#file-based-apps)
+- [Model Context Protocol Specification](https://spec.modelcontextprotocol.io/)