.NET: skill as class

[SergeyMenshykh]

Summary

Add class-based skills so skills can be distributed and reused as first-class C# types (for example from shared libraries/NuGet packages).

Changes

• Introduce a class-based skill type for programmatic skill definitions.
• Allow registering and using these skills through the existing skills source/provider pipeline.
• Keep support for existing skill sources (file-based and inline) while enabling reusable class-based packaging.

Closes: #4350

[Copilot]

Pull request overview

Adds support for class-based Agent Skills in the .NET implementation so skills can be packaged and reused as first-class C# types (e.g., from shared libraries/NuGet), while preserving existing file-based and inline skill flows.

Changes:

• Introduces AgentClassSkill and a shared XML content builder to synthesize skill content (name/description/instructions/resources/scripts).
• Broadens skill registration to accept AgentSkill instances (enabling inline + class-based skills through existing provider/source pipelines).
• Adds unit tests and expands the .NET AgentSkills samples to include class-based skills, DI-enabled variants, and mixed-source usage.

Reviewed changes

Copilot reviewed 29 out of 29 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
dotnet/tests/Microsoft.Agents.AI.UnitTests/AgentSkills/AgentSkillsProviderTests.cs	Adds provider tests covering class-based skills registration + deduplication.
dotnet/tests/Microsoft.Agents.AI.UnitTests/AgentSkills/AgentClassSkillTests.cs	New unit tests validating AgentClassSkill behavior and synthesized content.
dotnet/src/Microsoft.Agents.AI/Skills/Programmatic/AgentInlineSkillScript.cs	Exposes parameters schema via override to support generic script schema handling.
dotnet/src/Microsoft.Agents.AI/Skills/Programmatic/AgentInlineSkillContentBuilder.cs	New internal helper to build XML content for programmatic/class-based skills.
dotnet/src/Microsoft.Agents.AI/Skills/Programmatic/AgentInlineSkill.cs	Refactors inline skill content generation to use shared builder.
dotnet/src/Microsoft.Agents.AI/Skills/Programmatic/AgentClassSkill.cs	New abstract base type for class-packaged skills (instructions/resources/scripts).
dotnet/src/Microsoft.Agents.AI/Skills/AgentSkillsProviderBuilder.cs	Documentation updates clarifying advanced mixed-source builder usage.
dotnet/src/Microsoft.Agents.AI/Skills/AgentSkillsProvider.cs	Updates constructors to accept AgentSkill (not only inline skills).
dotnet/src/Microsoft.Agents.AI/Skills/AgentSkillScript.cs	Adds virtual ParametersSchema to unify schema exposure across script types.
dotnet/samples/02-agents/AgentSkills/README.md	Updates overview to include class-based skills and mixed/DI samples.
dotnet/samples/02-agents/AgentSkills/Agent_Step06_ClassBasedSkillsWithDI/README.md	New sample documentation for DI with class-based skills.
dotnet/samples/02-agents/AgentSkills/Agent_Step06_ClassBasedSkillsWithDI/Program.cs	New DI-enabled class-based skills sample implementation.
dotnet/samples/02-agents/AgentSkills/Agent_Step06_ClassBasedSkillsWithDI/Agent_Step06_ClassBasedSkillsWithDI.csproj	New sample project file for Step06.
dotnet/samples/02-agents/AgentSkills/Agent_Step05_CodeDefinedSkillsWithDI/README.md	New sample documentation for DI with inline (code-defined) skills.
dotnet/samples/02-agents/AgentSkills/Agent_Step05_CodeDefinedSkillsWithDI/Program.cs	New DI-enabled inline skills sample implementation.
dotnet/samples/02-agents/AgentSkills/Agent_Step05_CodeDefinedSkillsWithDI/Agent_Step05_CodeDefinedSkillsWithDI.csproj	New sample project file for Step05.
dotnet/samples/02-agents/AgentSkills/Agent_Step04_MixedSkills/skills/unit-converter/SKILL.md	New file-based skill content for mixed-skills sample.
dotnet/samples/02-agents/AgentSkills/Agent_Step04_MixedSkills/skills/unit-converter/scripts/convert-units.py	New script used by file-based skill in mixed sample.
dotnet/samples/02-agents/AgentSkills/Agent_Step04_MixedSkills/skills/unit-converter/references/unit-conversion-table.md	New reference document for file-based unit conversion skill.
dotnet/samples/02-agents/AgentSkills/Agent_Step04_MixedSkills/README.md	New documentation for advanced mixed skills sample.
dotnet/samples/02-agents/AgentSkills/Agent_Step04_MixedSkills/Program.cs	New mixed skills sample combining file + inline + class-based skills.
dotnet/samples/02-agents/AgentSkills/Agent_Step04_MixedSkills/Agent_Step04_MixedSkills.csproj	New sample project file for Step04 (copies skills to output).
dotnet/samples/02-agents/AgentSkills/Agent_Step03_ClassBasedSkills/README.md	New documentation for basic class-based skills sample.
dotnet/samples/02-agents/AgentSkills/Agent_Step03_ClassBasedSkills/Program.cs	New class-based skills sample implementation.
dotnet/samples/02-agents/AgentSkills/Agent_Step03_ClassBasedSkills/Agent_Step03_ClassBasedSkills.csproj	New sample project file for Step03.
dotnet/samples/02-agents/AgentSkills/Agent_Step01_FileBasedSkills/README.md	Minor terminology correction (“script runner” wording).
dotnet/filtered-unit.slnx	Adds a filtered solution file (currently appears to be a generated artifact).
dotnet/AGENTS.md	Updates .NET guidance to require Async suffix on async test methods.
dotnet/agent-framework-dotnet.slnx	Adds new AgentSkills sample projects to the main solution.

[peibekwe]

nit: Could some of these samples be merged with others (e.g. DI and non-DI related samples merged into one project) to reduce the number of sample projects we have?