[dotnet-port-api] Add compaction-backed history provider

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Summary

Add a compaction-backed history provider in agent/compaction so Go agents can apply reducer-triggered history compaction directly on the history-provider surface instead of only through a separate context provider. The change adds the new provider, covers compacted persistence and summary replay in tests, updates the additional-context sample to use the new API, and refreshes the parity doc to reflect the reduced .NET chat-history gap.

Ported .NET PRs

• None — this is a Go misalignment realignment for the documented .NET chat-history reducer-trigger capability. The local parity baseline tracks .NET commit 5996105a1bf2726918101adc6e9c9857b7f68b98, with workflow/test delta previously checked through 6a0773ba2180e8036d138dbb9794ae64ec2d978b.

Breaking Changes

No.

Tests and Examples

• go test ./agent ./agent/compaction ./examples/02-agents/agents/step17_additional_ai_context
• Added agent/compaction/historyprovider_test.go
• Updated examples/02-agents/agents/step17_additional_ai_context/main.go

Notes

• The live upstream-agent-framework/main fetch was blocked in this environment, so this PR ports the documented chat-history parity gap as a narrow Go realignment instead of tying the change to a freshly inspected upstream PR.
• Other broader chat-history/storage parity gaps remain out of scope for this PR.

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Show patch preview (49 of 382 lines)

From 1681aba4204460f1c46f2bd66efdd44915c5e54b Mon Sep 17 00:00:00 2001
X-GH-AW-Base-Commit: de821aaf3899669a99a730f66f25ebad31cba62c
From: "github-actions[bot]" <github-actions[bot]@users.noreply.github.com>
Date: Fri, 11 Sep 2026 05:37:42 +0000
Subject: [PATCH] [dotnet-port-api] Add compaction-backed history provider

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 agent/compaction/doc.go                       |   6 +-
 agent/compaction/historyprovider.go           | 188 ++++++++++++++++++
 agent/compaction/historyprovider_test.go      | 103 ++++++++++
 docs/dotnet-go-sdk-feature-comparison.md      |   2 +-
 .../step17_additional_ai_context/main.go      |  11 +-
 5 files changed, 305 insertions(+), 5 deletions(-)
 create mode 100644 agent/compaction/historyprovider.go
 create mode 100644 agent/compaction/historyprovider_test.go

diff --git a/agent/compaction/doc.go b/agent/compaction/doc.go
index d4280fe..6b4abab 100644
--- a/agent/compaction/doc.go
+++ b/agent/compaction/doc.go
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft. All rights reserved.
 
 // Package compaction reduces conversation history to fit a model's context
-// window. It provides a context provider and composable strategies — sliding
-// window, truncation, summarization, tool-result eviction, and context-window
-// sizing — selected by triggers evaluated over a message index.
+// window. It provides history and context providers plus composable strategies
+// — sliding window, truncation, summarization, tool-result eviction, and
+// context-window sizing — selected by triggers evaluated over a message index.
 package compaction
diff --git a/agent/compaction/historyprovider.go b/agent/compaction/historyprovider.go
new file mode 100644
index 0000000..7fcc9db
--- /dev/null
+++ b/agent/compaction/historyprovider.go
@@ -0,0 +1,188 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+package compaction
+
+import (
+	"cmp"
+	"context"
+	"log/slog"
+	"runtime"
+	"slices"
+	"sync
... (truncated)

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Generated by .NET to Go API Porting Agent · copilot · gpt54 · 187.4 AIC · ⌖ 10.6 AIC · ⊞ 19K · ◷

[michelle-clayton-work]

Pull request #1092 is linked to this issue and will close it when merged.