.NET: Harness Feature branch

[westey (westey-m)]

Motivation and Context

#5271

Description

• Adding components that make it easier to construct an Agent Harness with samples that demonstrate their usage.

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? If yes, add "[BREAKING]" prefix to the title of the PR.

[Copilot]

Pull request overview

Adds a “Harness” feature set to the .NET Agent Framework, including built-in AIContextProviders (todos, agent mode, file-memory) plus a context-window-derived compaction strategy, with accompanying unit tests and a runnable sample.

Changes:

• Introduces TodoProvider, AgentModeProvider, and FileMemoryProvider (with AgentFileStore + InMemoryAgentFileStore) for reusable harness tooling.
• Adds ContextWindowCompactionStrategy and tests validating threshold behavior.
• Adds a new interactive “Harness” sample (shared console + research step) and wires it into solution/docs; updates JSON source-gen registrations and package references.

Reviewed changes

Copilot reviewed 33 out of 33 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
dotnet/tests/Microsoft.Agents.AI.UnitTests/Harness/Todo/TodoProviderTests.cs	Adds unit coverage for todo harness provider tools + session persistence.
dotnet/tests/Microsoft.Agents.AI.UnitTests/Harness/FileMemory/InMemoryAgentFileStoreTests.cs	Adds unit coverage for in-memory file store CRUD, listing, search, and path validation.
dotnet/tests/Microsoft.Agents.AI.UnitTests/Harness/FileMemory/FileMemoryProviderTests.cs	Adds unit coverage for file-memory provider tools, state init/persistence, and traversal protection.
dotnet/tests/Microsoft.Agents.AI.UnitTests/Harness/AgentMode/AgentModeProviderTests.cs	Adds unit coverage for agent mode provider tools, helpers, constants, and state persistence.
dotnet/tests/Microsoft.Agents.AI.UnitTests/Compaction/ContextWindowCompactionStrategyTests.cs	Adds tests for compaction thresholds/validation and pipeline behavior.
dotnet/src/Microsoft.Agents.AI/Microsoft.Agents.AI.csproj	Adds Microsoft.Extensions.FileSystemGlobbing dependency for glob filtering.
dotnet/src/Microsoft.Agents.AI/Harness/Todo/TodoState.cs	Introduces persisted todo state model.
dotnet/src/Microsoft.Agents.AI/Harness/Todo/TodoProvider.cs	Adds todo AIContextProvider exposing add/complete/remove/query tools.
dotnet/src/Microsoft.Agents.AI/Harness/Todo/TodoItemInput.cs	Adds tool input model for creating todos.
dotnet/src/Microsoft.Agents.AI/Harness/Todo/TodoItem.cs	Adds public todo item model returned by tools/helpers.
dotnet/src/Microsoft.Agents.AI/Harness/FileMemory/InMemoryAgentFileStore.cs	Adds in-memory file store implementation with list/search/glob/regex + path normalization.
dotnet/src/Microsoft.Agents.AI/Harness/FileMemory/FileSearchResult.cs	Adds file-search result DTO for tool responses.
dotnet/src/Microsoft.Agents.AI/Harness/FileMemory/FileSearchMatch.cs	Adds per-line match DTO with line numbers.
dotnet/src/Microsoft.Agents.AI/Harness/FileMemory/FileMemoryState.cs	Adds persisted state for file-memory provider (working folder).
dotnet/src/Microsoft.Agents.AI/Harness/FileMemory/FileMemoryProvider.cs	Adds file-memory AIContextProvider exposing save/read/delete/list/search tools.
dotnet/src/Microsoft.Agents.AI/Harness/FileMemory/FileListEntry.cs	Adds list-files entry DTO including optional description.
dotnet/src/Microsoft.Agents.AI/Harness/FileMemory/AgentFileStore.cs	Introduces abstract file-store contract + glob matcher helpers.
dotnet/src/Microsoft.Agents.AI/Harness/AgentMode/AgentModeState.cs	Introduces persisted mode state model.
dotnet/src/Microsoft.Agents.AI/Harness/AgentMode/AgentModeProvider.cs	Adds mode-tracking AIContextProvider with get/set tools and public helpers.
dotnet/src/Microsoft.Agents.AI/Compaction/ContextWindowCompactionStrategy.cs	Adds compaction strategy that derives token thresholds from model constraints.
dotnet/src/Microsoft.Agents.AI/AgentJsonUtilities.cs	Registers harness DTO/state types for JSON source generation.
dotnet/samples/02-agents/README.md	Links new Harness sample set from samples index.
dotnet/samples/02-agents/Harness/README.md	Adds Harness samples landing page.
dotnet/samples/02-agents/Harness/Harness_Step01_Research/WebBrowsingTools.cs	Adds a simple web browsing tool used by the Harness research sample.
dotnet/samples/02-agents/Harness/Harness_Step01_Research/README.md	Documents the Harness research step sample usage and workflow.
dotnet/samples/02-agents/Harness/Harness_Step01_Research/Program.cs	Implements interactive research agent wiring harness providers + compaction + web tools.
dotnet/samples/02-agents/Harness/Harness_Step01_Research/Harness_Step01_Research.csproj	Adds project definition for the research sample.
dotnet/samples/02-agents/Harness/Harness_Shared_Console/ToolCallFormatter.cs	Adds formatting for tool calls in the shared console harness.
dotnet/samples/02-agents/Harness/Harness_Shared_Console/Spinner.cs	Adds console spinner used during streaming output.
dotnet/samples/02-agents/Harness/Harness_Shared_Console/Harness_Shared_Console.csproj	Adds shared console project for Harness samples.
dotnet/samples/02-agents/Harness/Harness_Shared_Console/HarnessConsole.cs	Adds reusable interactive console loop with streaming + commands.
dotnet/agent-framework-dotnet.slnx	Adds new Harness sample projects/files into the solution structure.
dotnet/Directory.Packages.props	Pins Microsoft.Extensions.FileSystemGlobbing package version.