Remove AI Tool Reduction experimental APIs

[Copilot]

• Delete source files:
  • src/Libraries/Microsoft.Extensions.AI.Abstractions/ToolReduction/IToolReductionStrategy.cs
  • src/Libraries/Microsoft.Extensions.AI/ToolReduction/ToolReducingChatClient.cs
  • src/Libraries/Microsoft.Extensions.AI/ToolReduction/EmbeddingToolReductionStrategy.cs
  • src/Libraries/Microsoft.Extensions.AI/ToolReduction/ChatClientBuilderToolReductionExtensions.cs
• Delete test file: test/Libraries/Microsoft.Extensions.AI.Integration.Tests/ToolReductionTests.cs
• Remove tool reduction integration tests and RemoveToolAfterFirstUseStrategy helper class from ChatClientIntegrationTests.cs
• Remove dead EmbeddingGenerator property, CreateEmbeddingGenerator(), and EnsureEmbeddingGenerator() members (and stale "tool reduction" comment) from ChatClientIntegrationTests.cs
• Remove AIToolReduction diagnostic ID from DiagnosticIds.cs
• Remove tool reduction entries from API baseline JSON files (Microsoft.Extensions.AI.json and Microsoft.Extensions.AI.Abstractions.json)
• Revert CHANGELOG.md changes per reviewer request
• Restore using System.Diagnostics.CodeAnalysis; needed for [MemberNotNull] on SkipIfNotEnabled
• Remove orphaned CreateEmbeddingGenerator() override from OpenAIChatClientIntegrationTests (no references in any tests)
• Add CompatibilitySuppressions.xml for both AI packages to suppress baseline compatibility errors for removed experimental types

Original prompt

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This section details on the original issue you should resolve

<issue_title>Remove AI Tool Reduction experimental APIs</issue_title>
<issue_description>> Many of the emerging approaches operate at the agent level rather than the chat client level, so it's unclear that IChatClient middleware is even the right layer for this. Either way, I don't think it makes sense to commit to a first-class MEAI abstraction in this PR. This can still be implemented as custom middleware by anyone who needs it today 🙂

Originally posted by @MackinnonBuck in #6865 (comment)

Per this conclusion, we should remove the experimental APIs related to tool reduction.</issue_description>

<agent_instructions>Remove all tool-reduction related APIs and associated tests, docs, etc. There's an interface, some With methods, etc</agent_instructions>

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

• Fixes Remove AI Tool Reduction experimental APIs #7352

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Microsoft Reviewers: Open in CodeFlow

[stephentoub]

@copilot, other than in the changelog, are there any remaining references anywhere in the repo in any kind of file to tool reduction, tool reducers, etc.?

[Copilot]

@copilot, other than in the changelog, are there any remaining references anywhere in the repo in any kind of file to tool reduction, tool reducers, etc.?

Yes — there was one remaining reference in ChatClientIntegrationTests.cs: a comment mentioning "tool reduction" as a use case, along with the dead EmbeddingGenerator property, CreateEmbeddingGenerator(), and EnsureEmbeddingGenerator() methods that were left behind when the tool-reduction tests were removed (none of them were called or overridden anywhere). All cleaned up in 3b8fd64. The CHANGELOG.md entry is the only remaining reference in the repo.

[Copilot]

Pull request overview

This PR removes the experimental “tool reduction” surface area from the Microsoft.Extensions.AI stack (APIs, middleware, diagnostic ID, and associated integration tests), aligning with the decision to not commit to a first-class MEAI abstraction for tool reduction.

Changes:

• Deleted the tool reduction abstractions and implementations (IToolReductionStrategy, ToolReducingChatClient, EmbeddingToolReductionStrategy, and builder extensions).
• Removed tool-reduction-focused integration tests and updated integration test baselines accordingly.
• Removed the associated experimental diagnostic ID and API baseline entries.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
test/Libraries/Microsoft.Extensions.AI.Integration.Tests/ToolReductionTests.cs	Removes unit/integration coverage dedicated to tool reduction strategies and middleware.
test/Libraries/Microsoft.Extensions.AI.Integration.Tests/ChatClientIntegrationTests.cs	Deletes tool reduction scenarios and embedding-generator plumbing that existed to support them.
src/Shared/DiagnosticIds/DiagnosticIds.cs	Removes the AIToolReduction experiment diagnostic constant.
src/Libraries/Microsoft.Extensions.AI/ToolReduction/ToolReducingChatClient.cs	Deletes the tool-reducing delegating chat client middleware.
src/Libraries/Microsoft.Extensions.AI/ToolReduction/EmbeddingToolReductionStrategy.cs	Deletes the embedding-based tool reduction strategy implementation.
src/Libraries/Microsoft.Extensions.AI/ToolReduction/ChatClientBuilderToolReductionExtensions.cs	Deletes UseToolReduction pipeline extension.
src/Libraries/Microsoft.Extensions.AI/Microsoft.Extensions.AI.json	Removes tool reduction types from the AI library API baseline.
src/Libraries/Microsoft.Extensions.AI.Abstractions/ToolReduction/IToolReductionStrategy.cs	Deletes the tool reduction strategy abstraction from the abstractions package.
src/Libraries/Microsoft.Extensions.AI.Abstractions/Microsoft.Extensions.AI.Abstractions.json	Removes IToolReductionStrategy from the abstractions API baseline.

[Copilot]

@copilot, other than in the changelog, are there any remaining references anywhere in the repo in any kind of file to tool reduction, tool reducers, etc.?

The only remaining reference is in CHANGELOG.md (line 46), which was intentionally kept. No other files in the repo reference tool reduction, tool reducers, IToolReductionStrategy, AIToolReduction, etc.

[stephentoub]

@copilot fix the CI failures by updating the compatibility suppressions

[Copilot]

@copilot fix the CI failures by updating the compatibility suppressions

Added auto-generated CompatibilitySuppressions.xml files for both Microsoft.Extensions.AI and Microsoft.Extensions.AI.Abstractions in 916d3f6. These suppress CP0001 baseline compatibility errors for the removed types (IToolReductionStrategy, ToolReducingChatClient, EmbeddingToolReductionStrategy, ChatClientBuilderToolReductionExtensions) across all TFMs.