.NET Compaction - Introduce preconfigured CompactionStrategy pattern

[Copilot]

Developers shouldn't need to understand internal strategy parameters to get a well-tuned compaction pipeline. This adds a CompactionStrategy.Create(approach, size, chatClient?) factory that maps two intuitive axes to a pre-configured PipelineCompactionStrategy.

New types

• CompactionApproach — controls pipeline composition:

  • Gentle: tool-result collapsing + LLM summarization
  • Balanced: tool-result collapsing + LLM summarization + truncation backstop
  • Aggressive: tool-result collapsing + LLM summarization + sliding window + truncation

• CompactionSize — scales all trigger thresholds to match model context capacity:

  • Compact ≈ 8 K tokens, Moderate ≈ 32 K tokens, Generous ≈ 64 K tokens

Factory logic

Within each pipeline, early stages trigger at a fraction of the size limit (⅔ for Balanced, ½ for Aggressive) so incremental compaction fires before reaching the emergency truncation backstop.

Usage

IChatClient summarizerClient = ...;

// Balanced pipeline for a mid-range model
CompactionStrategy strategy = CompactionStrategy.Create(
    CompactionApproach.Balanced,
    CompactionSize.Moderate,
    summarizerClient);

// Gentle pipeline — no LLM required
CompactionStrategy strategy = CompactionStrategy.Create(
    CompactionApproach.Gentle,
    CompactionSize.Compact);

chatClient is required (and validated) only when approach is Balanced or Aggressive.

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.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>.NET Compaction - Introduce preconfigured CompactionStrategy pattern</issue_title>
<issue_description>I expect many developers will ask: How do I configured my CompactionStrategy? ...which one do I use? ...what thresholds work best?

We can expose a factory that creates a pre-configured CompactionStrategy according to a set of options:

// Setup a chat client for summarization
IChatClient summarizingChatClient = ...;

// Create a compaction strategy based on a menu selection of characteristics
CompactionStrategy tunedStrategy =
   CompactionStrategy.Create(
      Approach.Balanced,
      Size.Compact,
      summarizingChatClient);

In this example, "size" could be:

• Compact
• Moderate
• Generous

And "approach" could be:

• Aggressive
• Balanced
• Gentle

Perhaps the "size" parameter is informed by the maximum input tokens allowed by a given model, with a default based on a conservative estimate of the most common usage.

Behind the scenes the combination of these two axes map to a certain CompactionStrategy configuration. As we improve our configuration, developers using this pattern will automatically realize those improvements.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes .NET Compaction - Introduce preconfigured CompactionStrategy pattern #4603

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[Copilot]

Pull request overview

This PR introduces a preconfigured compaction “menu” for the .NET Agent Framework, adding a CompactionStrategy.Create(approach, size, chatClient?) factory that maps high-level options to a tuned PipelineCompactionStrategy.

Changes:

• Added CompactionApproach and CompactionSize enums to represent the two configuration axes.
• Implemented CompactionStrategy.Create(...) factory to generate Gentle/Balanced/Aggressive pipelines with staged triggers.
• Added unit tests validating pipeline composition, argument validation, and (partially) size behavior.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
dotnet/src/Microsoft.Agents.AI/Compaction/CompactionStrategy.cs	Marks CompactionStrategy as partial to allow adding the factory in a separate file.
dotnet/src/Microsoft.Agents.AI/Compaction/CompactionStrategy.Factory.cs	Adds CompactionStrategy.Create(...) and internal size→threshold mappings for pipeline construction.
dotnet/src/Microsoft.Agents.AI/Compaction/CompactionApproach.cs	Adds the CompactionApproach enum describing pipeline composition choices.
dotnet/src/Microsoft.Agents.AI/Compaction/CompactionSize.cs	Adds the CompactionSize enum describing context-size profiles.
dotnet/tests/Microsoft.Agents.AI.UnitTests/Compaction/CompactionStrategyCreateTests.cs	Adds unit tests for the new factory method and size differentiation behavior.