[dotnet-port-api] Port message source attribution helpers

[github-actions]

Summary

Port the small .NET message-source attribution helper surface to Go by adding message.Message helpers for reading and applying request message source attribution.

This change adds (*message.Message).SourceType(), (*message.Message).SourceID(), and (*message.Message).WithSource(...), then reuses WithSource in the context-provider, history-provider, and middleware source-stamping paths. It also updates the feature comparison matrix to mark this helper surface as aligned.

Ported .NET PRs

• .NET: [BREAKING] Add ability to mark the source of Agent request messages and use that for filtering agent-framework#3540 - add request message source tagging/filtering support
• .NET: [BREAKING] Update message source code to match python. agent-framework#3805 - refine message source attribution to expose source type and source id helpers

Relevant upstream commits:

• ad0dac3c86201dc7dc1cd4866ba7e4502a910a0d
• 7dccf3a07bc5fd76004b85305f5121712e188b15

Breaking Changes

No.

Tests and Examples

• go test ./...
• Added message/message_test.go coverage for default source type, explicit source id/type access, and clone-vs-reuse behavior in WithSource
• No example changes were needed because the underlying source attribution workflow already existed; this PR ports the missing helper API surface

Notes

• This is a narrow API-parity PR focused on the helper surface called out in docs/dotnet-go-sdk-feature-comparison.md
• Broader history-provider reducer-trigger parity remains out of scope for this PR

Generated by .NET to Go API Porting Agent · 1.2K AIC · ⌖ 24.1 AIC · ⊞ 21.7K · ◷

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Show patch preview (185 of 185 lines)

From b502c38be66ea9315c3b34a84d03e83b82154209 Mon Sep 17 00:00:00 2001
From: "github-actions[bot]" <github-actions[bot]@users.noreply.github.com>
Date: Tue, 28 Jul 2026 06:25:28 +0000
Subject: [PATCH] [dotnet-port-api] Port message source attribution helpers

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 agent/context.go                         |  7 +---
 agent/history.go                         |  7 +---
 agent/middleware.go                      |  4 +-
 docs/dotnet-go-sdk-feature-comparison.md |  2 +-
 message/message.go                       | 31 ++++++++++++++
 message/message_test.go                  | 52 ++++++++++++++++++++++++
 6 files changed, 87 insertions(+), 16 deletions(-)

diff --git a/agent/context.go b/agent/context.go
index 40c3baa58..5d8c144ea 100644
--- a/agent/context.go
+++ b/agent/context.go
@@ -135,12 +135,7 @@ func (p *defaultContextProvider) Invoking(ctx context.Context, invoking Invoking
 	if len(providedMessages) > 0 {
 		source := message.Source{Type: SourceTypeContextProvider, ID: p.config.SourceID}
 		for i, msg := range providedMessages {
-			if msg == nil || msg.Source == source {
-				continue
-			}
-			marked := msg.Clone()
-			marked.Source = source
-			providedMessages[i] = marked
+			providedMessages[i] = msg.WithSource(source)
 		}
 		outMessages = append(outMessages, providedMessages...)
 	}
diff --git a/agent/history.go b/agent/history.go
index 348175eb6..ef92fa038 100644
--- a/agent/history.go
+++ b/agent/history.go
@@ -109,12 +109,7 @@ func (p *defaultHistoryProvider) Invoking(ctx context.Context, invoking Invoking
 
 	source := message.Source{Type: SourceTypeHistoryProvider, ID: p.config.SourceID}
 	for i, msg := range providedMessages {
-		if msg == nil || msg.Source == source {
-			continue
-		}
-		marked := msg.Clone()
-		marked.Source = source
-		providedMessages[i] = marked
+		providedMessages[i] = msg.WithSource(source)
 	}
 	outMessages := append(providedMessages, invoking.Messages...)
 
d
... (truncated)

[michelle-clayton-work]

Pull request #1000 is linked to this issue and will close it when merged.