feat: add MCP 2026 support

[douglance]

Summary

• add stateless MCP 2026 handling with server/discover, protocol routing, metadata, cache hints, resources, prompts, apps, subscriptions, tasks, and authorization extensions
• add MCP elicitation helpers for form and URL flows, including MRTR and task input resumption
• document the added MCP surface and include a minor changeset

Testing

• pnpm check
• pnpm check:types
• pnpm test src/Mcp.test.ts src/Cli.test-d.ts
• pnpm build
• pnpm test

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/incur@158

commit: 26e04dc

[codecov]

Codecov Report

❌ Patch coverage is 86.69202% with 70 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (main@e910ba6). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
src/Mcp.ts	87.97%	46 Missing and 8 partials ⚠️
src/Elicitation.ts	71.69%	10 Missing and 5 partials ⚠️
src/Cli.ts	95.65%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #158   +/-   ##
=======================================
  Coverage        ?   92.31%           
=======================================
  Files           ?       25           
  Lines           ?     3773           
  Branches        ?     1497           
=======================================
  Hits            ?     3483           
  Misses          ?      240           
  Partials        ?       50           

☔ View full report in Codecov by Harness.
📢 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.