Upgrade to MCP C# SDK 2.0 (2026-07-28 spec)

Summary

Adopt the MCP C# SDK 2.0 (modelcontextprotocol/csharp-sdk v2.0.x), aligned with the 2026-07-28 MCP specification. This is a tracking issue for the upgrade from ModelContextProtocol 1.4.0 ΓåÆ 2.0.x.

SDK 2.0 is backward-compatible at the protocol level (clients/servers auto-negotiate down to the legacy initialize handshake). API-surface breaks are limited to (1) capabilities deprecated by the new spec and (2) experimental APIs whose contracts changed ΓÇö both of which this server uses.

Upstream references:

• SDK 2.0 spec-compliance tracker: modelcontextprotocol/csharp-sdk#1539
• Preview 1 release notes: https://github.com/modelcontextprotocol/csharp-sdk/releases/tag/v2.0.0-preview.1

Current usage that's affected

• ModelContextProtocol 1.4.0 in DotNetMcp/DotNetMcp.csproj and DotNetMcp.Tests/DotNetMcp.Tests.csproj
• Microsoft.AgentGovernance.Extensions.ModelContextProtocol 4.0.0 (third-party, pinned to 1.x SDK)
• stdio transport only
• Experimental Tasks API (IMcpTaskStore / InMemoryMcpTaskStore)
• Roots (WorkspaceDiscovery), Sampling (AI error interpretation), Logging notifications (SendMcpLogAsync), Elicitation (destructive-op confirmation)
• Custom McpErrorCodes (uses -32002)
• MCP Apps resources

Work items

Required (to compile/run on 2.0)

• #482 ΓÇö Gating: confirm a 2.0-compatible Microsoft.AgentGovernance.Extensions.ModelContextProtocol
• #483 ΓÇö Bump ModelContextProtocol 1.4.0 ΓåÆ 2.0.x in both projects
• #484 ΓÇö Rewrite Tasks integration (remove IMcpTaskStore/InMemoryMcpTaskStore; adopt SEP-2663 Tasks extension)
• #485 ΓÇö Address Roots/Sampling/Logging deprecations (MCP9005)
• #486 ΓÇö Migrate Elicitation to MRTR and verify legacy back-compat
• #487 ΓÇö Review error codes (-32002 deprecation, renumbered protocol codes)
• #488 ΓÇö Fix tests (removed Tasks types, required Tool.InputSchema, error-code assertions)
• #489 ΓÇö Update documentation

Opportunities (spec-aligned improvements)

• #490 ΓÇö TTL for list results (SEP-2549) using existing caching infrastructure
• #491 ΓÇö JSON Schema 2020-12 output schemas (SEP-2106)
• #492 ΓÇö First-class MCP Apps APIs (McpApps.ExtensionId, [McpAppUi])
• #493 ΓÇö OpenTelemetry trace-context propagation (SEP-414)

Timing

Preview 1 only; the spec finalizes 2026-07-28 and open spec PR modelcontextprotocol/modelcontextprotocol#2776 may still shift behavior. Plan: prototype on a branch now (Tasks rewrite + governance-package compatibility), hold the version bump until a stable 2.0 and a 2.0-ready governance package are available.

Start with DotNetMcp/DotNetMcp.csproj and DotNetMcp.Tests/DotNetMcp.Tests.csproj, then read the SDK 2.0 spec-compliance tracker and preview release notes. Review child issues #482–#493, especially the Tasks and governance-package work, before changing the version. Done means the required migration work is complete, tests pass, and a stable 2.0 SDK and compatible governance package are available.