Summary

Publishes a versioned documentation site while preserving existing unversioned v1 URLs, and refreshes v2 documentation for the stabilized Tasks implementation and MCP specification compatibility.

Review the deployed prototype at https://jeffhandley.com/mcp-csharp-sdk-docs/.

Multi-version site behavior

• Discovers the most recently published non-draft release for each major version (v1, v2, and so on) and builds that release tag into /vN/.
• Uses the newest published release as the default, including prereleases. The site root redirects to that version.
• Injects a version picker into every generated HTML page. It uses page-relative asset URLs, so it works on project Pages and the production custom domain, and switches versions while preserving the current documentation path when it exists.
• Marks prerelease versions with a PREVIEW pill in the picker and displays a matching prerelease documentation banner.
• Uses DocFX's active theme rather than the operating-system theme, and content-hashes picker CSS/JS references to avoid stale cached assets.
• Generates redirect pages for every deployed v1 page at its legacy unversioned path, preserving existing v1 permalinks. The finalizer also writes v1-redirects.json as the generated redirect map.

Publishing workflow

• Runs on release publication and manual dispatch.
• The standard path rebuilds all released major-version documentation from their release tags, while using the workflow branch for the publishing orchestration, picker assets, and finalization scripts.
• Manual dispatch accepts an optional docs_ref (branch, tag, or commit). It derives that ref's major version from VersionPrefix, rebuilds only the matching /vN/ content from the ref, and continues building every other version from releases. This supports documentation-only refreshes without minting a product release.
• The workflow remains guarded to publish only from modelcontextprotocol/csharp-sdk; the fork-only guard removal used for prototype validation is intentionally excluded from this PR.

Documentation updates

• Documents the stable ModelContextProtocol.Extensions.Tasks package, its 2026-07-28 protocol requirement, and its lack of compatibility with v1's experimental Tasks implementation on down-level connections.
• Documents v2 client/server compatibility with supported earlier MCP protocol versions, including 2025-11-25, with Tasks as the documented exception.
• Removes the obsolete legacy package-profile note and updates the roadmap with the 2026-07-28 board and 2.x authentication focus.
• Refines v2 documentation language to use date-specific protocol references, stable 2.0 wording, sentence-case subheadings, and a current experimental-API example.

Related 1.x documentation cleanup: #1729.

Validation

• dotnet docfx docs/docfx.json --warningsAsErrors true
• Fork Pages deployment succeeded: https://github.com/jeffhandley/mcp-csharp-sdk-docs/actions/runs/30036104079

dotnet test --no-build --no-restore has existing local integration failures because TestServer.exe is not on PATH.