.NET: Add Hosted-AgentSkills sample with Foundry Skills integration

[rogerbarreto]

Motivation and Context

Closes #5776 — .NET Hosted Agents Sample - Agent Skills Support.

Mirrors the Python Foundry Skills sample (PR #5822) for .NET, demonstrating how to load behavioral guidelines from Foundry Skills at startup using AgentSkillsProvider and the progressive disclosure pattern.

Description

New sample: Hosted-AgentSkills under dotnet/samples/04-hosting/FoundryHostedAgents/responses/

The agent:

1. Downloads SKILL.md files from Foundry via ProjectAgentSkills.DownloadSkillAsync (from Azure.AI.Projects.Agents SDK)
2. Extracts ZIP archives with zip-slip protection into downloaded_skills/<name>/
3. Wires them into AgentSkillsProvider as an AIContextProvider (progressive disclosure: advertise → load on demand)
4. Hosts via the Responses protocol (AddFoundryResponses / MapFoundryResponses)

Ships two Contoso Outdoors skills matching the Python sample:

• support-style — tone, formatting, signature guidelines (canary: STYLE-CANARY-3318)
• escalation-policy — when and how to escalate tickets (canary: ESC-CANARY-7742)

Key discovery: Azure.AI.Projects.Agents (transitive dep of Azure.AI.Projects 2.1.0-beta.2) already has ProjectAgentSkills with full skills CRUD — no raw REST needed.

Tests:

• 14 unit tests (ZIP extraction, skill name validation, AgentSkillsProvider integration) — all passing
• Container integration test scenario (agent-skills) with fixture and 4 tests
• Local smoke test (scripts/smoke.ps1)

Also: Updated commented-out PackageReference versions from 1.0.0 to latest NuGet across all 13 hosted samples.

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the Contribution Guidelines
• All unit tests pass, and I have added new tests where possible
• Is this a breaking change? No.

[Copilot]

Pull request overview

Adds a new .NET hosted agent sample demonstrating Foundry Skills integration and the progressive disclosure pattern via AgentSkillsProvider, plus accompanying unit/integration-test scaffolding and sample dependency-version comment updates.

Changes:

• New Hosted-AgentSkills sample: provisions (optional), downloads, extracts, and wires Foundry skills into a hosted Responses agent.
• Adds unit tests for ZIP extraction + skill name validation + AgentSkillsProvider behavior, and introduces an integration-test scenario/fixture for agent skills.
• Updates commented-out PackageReference versions across multiple existing hosted samples and registers the new sample in the .NET solution.

Reviewed changes

Copilot reviewed 32 out of 32 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
dotnet/tests/Microsoft.Agents.AI.UnitTests/Microsoft.Agents.AI.UnitTests.csproj	Excludes the new AgentSkills unit test from legacy TFMs.
dotnet/tests/Microsoft.Agents.AI.UnitTests/AgentSkills/HostedAgentSkillsPatternTests.cs	Adds unit tests covering ZIP extraction guardrails and provider behavior.
dotnet/tests/Foundry.Hosting.IntegrationTests/scripts/it-bootstrap-agents.ps1	Adds agent-skills to the integration test scenario bootstrap list.
dotnet/tests/Foundry.Hosting.IntegrationTests/README.md	Documents the new agent-skills integration scenario/fixture.
dotnet/tests/Foundry.Hosting.IntegrationTests/Fixtures/AgentSkillsHostedAgentFixture.cs	Adds fixture for the agent-skills hosted-agent integration scenario.
dotnet/tests/Foundry.Hosting.IntegrationTests/AgentSkillsHostedAgentTests.cs	Adds integration tests for skills advertisement/loading (currently skipped like other placeholder ITs).
dotnet/tests/Foundry.Hosting.IntegrationTests.TestContainer/Program.cs	Adds an agent-skills scenario wiring AgentSkillsProvider over on-disk skills.
dotnet/tests/Foundry.Hosting.IntegrationTests.TestContainer/Foundry.Hosting.IntegrationTests.TestContainer.csproj	Adds references needed by the new skills scenario in the test container.
dotnet/samples/04-hosting/FoundryHostedAgents/responses/Hosted-Workflow-Simple/HostedWorkflowSimple.csproj	Updates commented-out end-user package versions.
dotnet/samples/04-hosting/FoundryHostedAgents/responses/Hosted-Workflow-Handoff/HostedWorkflowHandoff.csproj	Updates commented-out end-user package versions.
dotnet/samples/04-hosting/FoundryHostedAgents/responses/Hosted-Toolbox/HostedToolbox.csproj	Updates commented-out end-user package versions.
dotnet/samples/04-hosting/FoundryHostedAgents/responses/Hosted-TextRag/HostedTextRag.csproj	Updates commented-out end-user package versions.
dotnet/samples/04-hosting/FoundryHostedAgents/responses/Hosted-Observability/HostedObservability.csproj	Updates commented-out end-user package versions.
dotnet/samples/04-hosting/FoundryHostedAgents/responses/Hosted-MemoryAgent/HostedMemoryAgent.csproj	Updates commented-out end-user package versions.
dotnet/samples/04-hosting/FoundryHostedAgents/responses/Hosted-McpTools/HostedMcpTools.csproj	Updates commented-out end-user package versions.
dotnet/samples/04-hosting/FoundryHostedAgents/responses/Hosted-LocalTools/HostedLocalTools.csproj	Updates commented-out end-user package versions.
dotnet/samples/04-hosting/FoundryHostedAgents/responses/Hosted-FoundryAgent/HostedFoundryAgent.csproj	Updates commented-out end-user package versions.
dotnet/samples/04-hosting/FoundryHostedAgents/responses/Hosted-Files/HostedFiles.csproj	Updates commented-out end-user package versions.
dotnet/samples/04-hosting/FoundryHostedAgents/responses/Hosted-ChatClientAgent/HostedChatClientAgent.csproj	Updates commented-out end-user package versions.
dotnet/samples/04-hosting/FoundryHostedAgents/responses/Hosted-AzureSearchRag/HostedAzureSearchRag.csproj	Updates commented-out end-user package versions.
dotnet/samples/04-hosting/FoundryHostedAgents/responses/Hosted-AgentSkills/skills/support-style/SKILL.md	Adds the sample “support-style” skill content.
dotnet/samples/04-hosting/FoundryHostedAgents/responses/Hosted-AgentSkills/skills/escalation-policy/SKILL.md	Adds the sample “escalation-policy” skill content.
dotnet/samples/04-hosting/FoundryHostedAgents/responses/Hosted-AgentSkills/scripts/smoke.ps1	Adds a local smoke-test script for the new sample.
dotnet/samples/04-hosting/FoundryHostedAgents/responses/Hosted-AgentSkills/README.md	Documents sample behavior, setup, and expected canary tokens.
dotnet/samples/04-hosting/FoundryHostedAgents/responses/Hosted-AgentSkills/Program.cs	Implements the sample: skill provisioning (optional), download, ZIP extraction, and hosting via Responses.
dotnet/samples/04-hosting/FoundryHostedAgents/responses/Hosted-AgentSkills/HostedAgentSkills.csproj	Adds the new sample project and publish-time inclusion of skills/.
dotnet/samples/04-hosting/FoundryHostedAgents/responses/Hosted-AgentSkills/Dockerfile.contributor	Adds contributor-focused Docker packaging instructions (pre-publish + copy output).
dotnet/samples/04-hosting/FoundryHostedAgents/responses/Hosted-AgentSkills/Dockerfile	Adds end-user Dockerfile (restore/publish in-container).
dotnet/samples/04-hosting/FoundryHostedAgents/responses/Hosted-AgentSkills/agent.yaml	Adds agent definition for Foundry deployment.
dotnet/samples/04-hosting/FoundryHostedAgents/responses/Hosted-AgentSkills/agent.manifest.yaml	Adds agent manifest with parameters and model resource mapping.
dotnet/samples/04-hosting/FoundryHostedAgents/responses/Hosted-AgentSkills/.env.example	Adds example environment configuration for local runs.
dotnet/agent-framework-dotnet.slnx	Registers the new Hosted-AgentSkills sample in the solution.

[rogerbarreto]

Re: zip-slip OrdinalIgnoreCase on case-sensitive FS (both comments)

Fixed in 6a22579 — now uses \OperatingSystem.IsWindows()\ to select \Ordinal\ on Unix vs \OrdinalIgnoreCase\ on Windows. Containers run Linux -> case-sensitive check applied. Same fix in test helper.