.NET: feat: Implement Magentic Orchestration for .NET

[lokitoth]

Motivation and Context

Magentic Orchestration allows users to build task-solving teams of Agents easily by relying on intelligent planning and orchestration of the plan using the available team, by routing dynamically around the workflow.

Description

Implement Magentic Orchestration

• Closes .NET: Add support for Magentic Orchestration #1275
• Closes .NET: [Feature]: When will .NET support Workflows Orchestrations - Magentic #5154

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

Note

Copilot was unable to run its full agentic suite in this review.

Implements Magentic Orchestration for .NET, adding a manager-driven planning + progress-ledger loop, orchestration events, and a fluent workflow builder.

Changes:

• Added Magentic orchestrator/manager/task-context and prompt templates to plan, coordinate rounds, track progress, and reset/replan.
• Introduced Magentic progress ledger + JSON extraction helpers and tool-call/result matching for transcript rendering.
• Added unit tests covering JSON extraction and progress-ledger state update/formatting behavior.

Reviewed changes

Copilot reviewed 20 out of 20 changed files in this pull request and generated 12 comments.

Show a summary per file

File	Description
dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/TestReplayAgent.cs	Extends replay agent to support multi-turn scripted outputs for orchestrator tests.
dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/TestProgressLedgerState.cs	Adds a test fixture for progress-ledger JSON state + validation helpers.
dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/MagenticProgressLedgerTests.cs	Adds tests for extracting JSON from chat messages and validating ledger init/update/schema.
dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/MagenticManagerTests.cs	Adds tests for plan updates, progress-ledger retries, and final-answer preparation.
dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowEvent.cs	Registers Magentic orchestration events for polymorphic serialization.
dotnet/src/Microsoft.Agents.AI.Workflows/Specialized/Magentic/StreamingToolCallResultPairMatcher.cs	Adds helper to pair tool calls with tool results across streaming updates.
dotnet/src/Microsoft.Agents.AI.Workflows/Specialized/Magentic/PromptTemplates.cs	Adds prompt templates for facts, plans, progress ledger, and final answer.
dotnet/src/Microsoft.Agents.AI.Workflows/Specialized/Magentic/MagenticTaskContext.cs	Adds task context/state export + counters/limits and ledger integration.
dotnet/src/Microsoft.Agents.AI.Workflows/Specialized/Magentic/MagenticOrchestrator.cs	Adds the core Magentic orchestration loop, replanning, events, and HITL plan review.
dotnet/src/Microsoft.Agents.AI.Workflows/Specialized/Magentic/MagenticManager.cs	Adds manager agent interactions for plan creation, ledger updates with retry, and final answer.
dotnet/src/Microsoft.Agents.AI.Workflows/Specialized/Magentic/MagenticConstants.cs	Adds constants for checkpoint persistence keys.
dotnet/src/Microsoft.Agents.AI.Workflows/Specialized/Magentic/ExecutorAgentHarness.cs	Adds an agent harness that optionally streams updates and tracks sessions.
dotnet/src/Microsoft.Agents.AI.Workflows/Specialized/Magentic/ChatMessageExtensions.cs	Adds transcript text extraction + fenced/embedded JSON extraction.
dotnet/src/Microsoft.Agents.AI.Workflows/Specialized/AIAgentHostExecutor.cs	Adds agent reset handling and exposes a stable executor id helper.
dotnet/src/Microsoft.Agents.AI.Workflows/ResetChatSignal.cs	Adds a signal type to request agent executors reset state/session.
dotnet/src/Microsoft.Agents.AI.Workflows/MagenticWorkflowBuilder.cs	Adds a fluent builder to assemble Magentic workflows and wire executors/edges.
dotnet/src/Microsoft.Agents.AI.Workflows/MagenticProgressLedger.cs	Adds progress-ledger state management + question/schema formatting.
dotnet/src/Microsoft.Agents.AI.Workflows/MagenticPlanReviewResponse.cs	Adds HITL plan review response type.
dotnet/src/Microsoft.Agents.AI.Workflows/MagenticPlanReviewRequest.cs	Adds HITL plan review request type + helpers to approve or revise.
dotnet/src/Microsoft.Agents.AI.Workflows/ExecutorEvent.cs	Updates executor events’ polymorphic serialization attributes.

Comments suppressed due to low confidence (1)

dotnet/src/Microsoft.Agents.AI.Workflows/ExecutorEvent.cs:1

• MagenticOrchestratorEvent derives from WorkflowEvent, not ExecutorEvent. Registering it as a derived type of ExecutorEvent can fail at runtime when building polymorphic metadata (derived type must be assignable to base type). Remove this [JsonDerivedType] from ExecutorEvent (keeping the registration on WorkflowEvent is sufficient).

// Copyright (c) Microsoft. All rights reserved.

[github-actions]

Automated Code Review

Reviewers: 2 | Confidence: 94% | Result: All clear

Reviewed: Test Coverage, Design Approach

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Automated review by lokitoth's agents

[github-actions]

Automated Code Review

Reviewers: 2 | Confidence: 93% | Result: All clear

Reviewed: Test Coverage, Design Approach

---

Automated review by lokitoth's agents