Summary

Documentation refinements for the 2.0.0 release: concept-doc corrections, a new Supporting down-level clients section for MRTR, navigation adjustments, and two corrections to the TasksExtension sample. Also incorporates review feedback from the PR discussion.

This is the first of two planned docs changes. A follow-up will introduce a compile-gated snippets project that transcludes all documentation code samples; it is parked separately so it can land cleanly on top of this once merged.

Concept documentation

• tasks.md — restore the intended information architecture: move Compatibility with v1 experimental Tasks under Architecture notes (from a top-level section right after the intro to #### Compatibility with v1 experimental Tasks, after Capability bypass inside a task scope and before Known limitations).
• capabilities.md — correct a client variable reference (mcpClient → client).
• index.md — list Stateless and Stateful under Base protocol to match toc.yml.
• getting-started.md, transports.md — standardize link text on Stateless and Stateful (the concept page's name) rather than Sessions.
• sampling.md, roots.md, logging.md — add deprecation notices for the Roots/Sampling/Logging utilities (SEP-2577); for sampling and roots, point to the stateless-compatible Multi round-trip requests (MRTR) alternative.
• list-of-diagnostics.md — link SEP-2577 from the MCP9005 row, and standardize the MCP9004 link text on Stateless and Stateful.
• logging.md — correct the Trace-level note: LogLevel.Trace maps to the MCP debug level when sent to the client (McpServerImpl.ToLoggingLevel); it is not silently dropped.
• Normalize stray trailing spaces in two docs-sample snippet markers.

MRTR — Supporting down-level clients

• mrtr.md — add a Supporting down-level clients section with two strategies (Return actionable guidance and Offer a non-interactive fallback) and a non-destructive CloseSupportTicket sample. The sample elicits a required closeReason and demonstrates four client scenarios in a single tool: explicit up-front input, an MRTR round-trip response, an MRTR initial request (with the SDK's automatic down-level elicitation bridge on a stateful session), and a session-less down-level natural-language fallback. This mirrors the sample used in the v2.0 announcement blog post.

Navigation

• concepts/toc.yml — add API Reference and Experimental APIs to the conceptual left-nav, after Extensions.
• toc.yml — remove Experimental APIs from the top-nav.
• versioning.md — add a See also section linking Experimental APIs and List of diagnostics.

TasksExtension sample

• Fix a startup crash by registering the in-memory transport via .WithStreamServerTransport(...), which registers the McpServer DI factory (regression from the Tasks extraction, Extract Tasks into the ModelContextProtocol.Extensions.Tasks extension package #1693). The sample now runs its task poll loop to completion.
• Sync the README with the current single CallToolAsTaskAsync manual-poll sample (the prior README described a pre-Extract Tasks into the ModelContextProtocol.Extensions.Tasks extension package #1693 two-path client that no longer exists), and remove a stale MCPEXP001 note.

Validation

• DocFX --warningsAsErrors: 0 warnings / 0 errors.
• samples/TasksExtension builds clean and runs the poll loop to completion.
• The CloseSupportTicket MRTR sample was validated over an HTTP harness across the full client/transport matrix (MRTR-capable and down-level clients; stateful and stateless transports), including the session-less down-level fallback path.