Handle MCP 2026 removed core RPCs

[leehack]

Summary

• Reject MCP 2026 stateless requests for core RPCs removed by SEP 2575: initialize, ping, logging/setLevel, resources/subscribe, and resources/unsubscribe.
• Reject removed stateless notifications while preserving metadata when parsing notifications/initialized and notifications/roots/list_changed.
• Add request-scoped stateless logging gating through io.modelcontextprotocol/logLevel metadata while preserving legacy session-level logging behavior.

Validation

• dart format .
• dart analyze
• dart test test/mcp_2026_07_28_test.dart
• dart test test/server/server_advanced_test.dart test/server/server_test.dart test/client/client_test.dart
• dart test -j 1
• git diff --check

Notes

This remains stacked on the MCP 2026 RC development branch and should not be merged to main or released as stable until the final spec is official.

[codecov]

Codecov Report

❌ Patch coverage is 97.77778% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 86.26%. Comparing base (5af9b80) to head (3ac1636).

Files with missing lines	Patch %	Lines
lib/src/server/mcp_server.dart	0.00%	1 Missing ⚠️

Additional details and impacted files

@@                       Coverage Diff                       @@
##           spec/2026-cacheable-results     #187      +/-   ##
===============================================================
+ Coverage                        86.16%   86.26%   +0.10%     
===============================================================
  Files                               46       46              
  Lines                             8362     8403      +41     
===============================================================
+ Hits                              7205     7249      +44     
+ Misses                            1157     1154       -3     

Flag	Coverage Δ
unittests	86.26% <97.77%> (+0.10%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[leehack]

Closing this draft micro PR because the RC spec work has been consolidated into a smaller reviewable stack. This change is preserved in #268 (MCP 2026 transport enforcement); the consolidated tip is tree-identical to the previous micro-stack tip.