.NET: Allow compaction for per-service-call local chat history

[Copilot]

Motivation & Context

CompactionProvider treats _agent_local_chat_history as a remote conversation ID, incorrectly skipping compaction when placed below the per-service-call history persistence client.

Description & Review Guide

• What are the major changes? Exempt the existing local-history sentinel from the remote-session skip condition.
• What is the impact of these changes? Local history can be compacted; real remote conversation IDs still bypass compaction.
• What do you want reviewers to focus on? Regression coverage for sentinel, null, empty, whitespace, and remote conversation IDs.

Related Issue

Contribution Checklist

• The code builds clean without any errors or warnings
• All unit tests pass, and I have added new tests where possible
• The PR follows the Contribution Guidelines
• This PR is linked to an issue and there is no other open PR for this issue (see Related Issue above).
• This is not a breaking change. If it is a breaking change, add the breaking change label (or add "[BREAKING]" to the title prefix, before or after any language prefix) — a workflow keeps the label and title prefix in sync automatically.

• Fixes .NET: Should we exclude cases where ConversationId="_agent_local_chat_history"? #8133

[Copilot]

Copilot wasn't able to review any files in this pull request. Check if the Files changed in this pull request are included in default exclusions.

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[github-code-quality]

Code Coverage Overview

Languages: C#

C# / code-coverage/dotnet

The overall line coverage in commit 25fc330 in the copilot/exclude-agen... branch is 85%. Line coverage data for the main branch is not yet available.

Show a line coverage summary of the most covered files.

File	main	copilot/exclude-agen... 25fc330	+/-
/home/runner/wo...valConverter.cs	—	100%	—
/home/runner/wo...entsProvider.cs	—	99%	—
/home/runner/wo...egatingAgent.cs	—	99%	—
/home/runner/wo...nticAnalyzer.cs	—	94%	—
/home/runner/wo...putConverter.cs	—	90%	—
/home/runner/wo...kflowBuilder.cs	—	90%	—
/home/runner/wo...SkillsSource.cs	—	89%	—
/home/runner/wo...onExtensions.cs	—	81%	—
/home/runner/wo...CopilotAgent.cs	—	76%	—
/home/runner/wo...ctionVisitor.cs	—	75%	—

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_{Updated September 29, 2026 16:23 UTC}