Add mcp-sdk-plain module: MCP server on the plain Java SDK 2.1.0 over stdio and Streamable HTTP, fat jar, wire transcripts and a Spring AI client

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_017ic4b5oh78z7gcH6QkxafF

mcp-sdk-plain/output/01-stdio-tour.txt

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+server: notes-server 1.0.0
+protocol: 2025-11-25
+capabilities: tools=true resources=true prompts=false
+instructions: Tools: word_stats, divide, explode. Resources: notes://readme and notes://{name}.
+-- tools/list
+word_stats required=[text]
+divide required=[a, b]
+explode required=null
+-- tools/call word_stats
+isError=false text=words=4 chars=19 longest=quick
+-- tools/call divide 1/0
+isError=true text=Cannot divide 1.0 by zero.
+-- tools/call word_stats with a missing argument
+isError=true text=Tool (word_stats) input validation failed: Validation failed: JSON schema validation errors: [: required property 'text' not found]
+-- tools/call explode
+threw McpError: boom from the handler
+-- resources/list
+notes://readme text/markdown
+-- resources/templates/list
+notes://{name}
+-- resources/read notes://readme
+# Notes server
+Built with the plain MCP Java SDK.
+-- resources/read notes://todo
+1. Write the post
+2. Run the server
+3. Publish
+-- resources/read notes://missing
+threw McpError: No note called missing