[SergeyMenshykh]

Motivation & Context

Enable skills/list discovery for MCP servers advertising the Skills extension, while preserving legacy discovery for older servers.

Description & Review Guide

• What are the major changes? Add capability-based discovery, validate skill metadata and resource manifests, and update the sample, docs, and tests.
• What is the impact of these changes? No public API changes. Listed skills load content lazily and restrict resource reads to their manifests. Supports one complete result with static resource lists, not the full extension. Legacy index/archive discovery is unchanged.
• What do you want reviewers to focus on? Discovery selection, validation, and backward compatibility.

Validated: 432 MCP unit tests, sample build, formatting, and sample MCP discovery/resource reads. The broader .NET suite was not run.

Related Issue

Related to #8772; follows #9198.

Contribution Checklist

• The code builds clean without any errors or warnings
• All unit tests pass, and I have added new tests where possible
• The PR follows the Contribution Guidelines
• This PR is linked to an issue and there is no other open PR for this issue (see Related Issue above).
• This is not a breaking change. If it is a breaking change, add the breaking change label (or add "[BREAKING]" to the title prefix, before or after any language prefix) — a workflow keeps the label and title prefix in sync automatically.

[Copilot]

🟡 Changes recommended

Required manifest integrity verification, pagination, identity handling, and specification-compliant sample fields are missing.

2 open findings

• Populate required Skills extension response fields · New
• Handle pagination until all skills are retrieved · New

What changed in this PR

Adds capability-based MCP skill discovery while retaining legacy index fallback.

Changes:

• Adds skills/list discovery and validation.
• Adds comprehensive discovery/resource tests.
• Updates the MCP sample and documentation.

File	Description
AgentMcpListedSkillsTests.cs	Tests listed-skill behavior.
InMemoryMcpServer.cs	Supports server option configuration.
AgentMcpSkillsSourceTests.cs	Tests legacy resource compatibility.
AgentMcpSkillsDiscoverySelectionTests.cs	Tests capability-based selection.
McpListedSkillsLoader.cs	Implements skills/list discovery.
AgentSkillsProviderBuilderMcpExtensions.cs	Documents discovery behavior.
AgentMcpSkillsSource.cs	Selects listed or legacy discovery.
AgentSkills/​README.md	Updates sample summary.
Agent_Step06_McpBasedSkills/​README.md	Documents the updated sample.
Agent_Step06_McpBasedSkills/​Program.cs	Implements a listed-skills server sample.

🧠 Review effort: Balanced

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[github-actions]

MAF Automated Review — Iteration 1

Result: Findings reported
Scope: full PR (1 commit(s)): 573235293d8e
Model: gpt-5.6-sol

Overview

The change cleanly selects skills/list from the exact advertised capability, validates metadata and resource manifests, confines reads to the held manifest, and preserves the legacy path when the extension is absent. The added tests cover selection, malformed responses, URI confinement, cancellation, origin binding, and lazy reads. Residual risk remains because a server-controlled complete manifest has no retention limits, and the new early return bypasses the archive directory cleanup contract.

Reviewed the supplied pull-request change set across correctness, security/reliability, architecture, and failure behavior.
2 verified findings remained after source verification (1 high, 1 medium) across 2 files. Details are attached to the affected lines below.

Affected areas: dotnet/src/Microsoft.Agents.AI.Mcp/Skills/AgentMcpSkillsSource.cs, dotnet/src/Microsoft.Agents.AI.Mcp/Skills/Listed/McpListedSkillsLoader.cs

[github-code-quality]

Code Coverage Overview

Languages: C#

C# / code-coverage/dotnet

The overall line coverage in commit cb17cdc in the sergeymenshykh-apply... branch remains at 85%, unchanged from commit fd52de7 in the feature-mcp-skills-n... branch.

Show a line coverage summary of the most impacted files.

File	feature-mcp-skills-n... fd52de7	sergeymenshykh-apply... cb17cdc	+/-
/home/runner/wo...ewChatClient.cs	67%	0%	-67%
/home/runner/wo...toryProvider.cs	95%	31%	-64%
/home/runner/wo...SessionStore.cs	100%	53%	-47%
/home/runner/wo...moryProvider.cs	84%	74%	-10%
/home/runner/wo...tateBagValue.cs	93%	89%	-4%
/home/runner/wo...CopilotAgent.cs	72%	76%	+4%
/home/runner/wo...SkillsSource.cs	69%	100%	+31%
/home/runner/wo...pListedSkill.cs	0%	95%	+95%
/home/runner/wo...SkillsLoader.cs	0%	100%	+100%
/home/runner/wo...killResource.cs	0%	100%	+100%

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_{Updated October 12, 2026 09:30 UTC}