.NET: fix: preserve AG-UI event metadata

[Yufeng He (he-yufeng)]

Summary

• preserve TextContent.AdditionalProperties as AG-UI passthrough fields on text start/content events
• preserve event passthrough fields when converting AG-UI text events back to TextContent
• carry DataContent.AdditionalProperties through state snapshot/delta events as the same passthrough metadata path
• filter event-owned fields like type, messageId, delta, and snapshot so metadata cannot shadow AG-UI protocol fields

Fixes #4923

Validation

• dotnet run --project dotnet\tests\Microsoft.Agents.AI.AGUI.UnitTests\Microsoft.Agents.AI.AGUI.UnitTests.csproj --framework net10.0 -- --filter-class Microsoft.Agents.AI.AGUI.UnitTests.ChatResponseUpdateAGUIExtensionsTests
• dotnet run --project dotnet\tests\Microsoft.Agents.AI.AGUI.UnitTests\Microsoft.Agents.AI.AGUI.UnitTests.csproj --framework net10.0
• dotnet format dotnet\agent-framework-dotnet.slnx --verify-no-changes --include dotnet\src\Microsoft.Agents.AI.AGUI\Shared\BaseEvent.cs dotnet\src\Microsoft.Agents.AI.AGUI\Shared\ChatResponseUpdateAGUIExtensions.cs dotnet\tests\Microsoft.Agents.AI.AGUI.UnitTests\ChatResponseUpdateAGUIExtensionsTests.cs
• git diff --check

[Copilot]

Pull request overview

This PR updates the .NET AG-UI adapter layer to preserve AIContent.AdditionalProperties as AG-UI “passthrough” JSON fields when converting between ChatResponseUpdate streams and AG-UI event streams, while filtering reserved protocol-owned field names so they can’t be shadowed by metadata.

Changes:

• Add JsonExtensionData support to AG-UI events (BaseEvent) to carry arbitrary passthrough fields.
• Preserve passthrough metadata across conversions (TextContent ↔ TEXT_MESSAGE_* events, DataContent ↔ STATE_* events) with reserved-field filtering.
• Add unit tests validating passthrough emission, filtering of reserved fields, and round-tripping back into AIContent.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
dotnet/src/Microsoft.Agents.AI.AGUI/Shared/BaseEvent.cs	Adds JsonExtensionData-backed AdditionalProperties for AG-UI passthrough fields on all events.
dotnet/src/Microsoft.Agents.AI.AGUI/Shared/ChatResponseUpdateAGUIExtensions.cs	Copies AdditionalProperties between AIContent and events and filters reserved protocol fields during event emission.
dotnet/tests/Microsoft.Agents.AI.AGUI.UnitTests/ChatResponseUpdateAGUIExtensionsTests.cs	Adds coverage for preserving passthrough metadata and ensuring reserved fields aren’t shadowed in serialized output.

[Yufeng He (he-yufeng)]

Addressed both review comments in a follow-up commit.

Changes:

• TextMessageBuilder now captures passthrough metadata from TextMessageStartEvent and merges it into emitted TextContent.AdditionalProperties.
• When the same key exists on START and CONTENT, the CONTENT value wins.
• BaseEventJsonConverter.Read now maps STATE_DELTA to StateDeltaEvent, matching the existing write path.
• Added tests for START metadata merging and STATE_DELTA BaseEvent deserialization.

Local validation:

dotnet build dotnet\tests\Microsoft.Agents.AI.AGUI.UnitTests\Microsoft.Agents.AI.AGUI.UnitTests.csproj --no-restore
dotnet dotnet\tests\Microsoft.Agents.AI.AGUI.UnitTests\bin\Debug\net10.0\Microsoft.Agents.AI.AGUI.UnitTests.dll --filter-method '*AsChatResponseUpdatesAsync_WithTextStartAdditionalProperties_PreservesAndMergesMetadataAsync' --filter-method '*BaseEventJsonConverter_WithStateDeltaEvent_DeserializesStateDeltaEvent' --filter-method '*AsAGUIEventStreamAsync_ConvertsDataContentWithJsonPatch_ToStateDeltaEventAsync' --filter-method '*AsChatResponseUpdatesAsync_WithTextEventAdditionalProperties_PreservesTextContentMetadataAsync' --no-progress
dotnet format dotnet\agent-framework-dotnet.slnx --verify-no-changes --no-restore --include dotnet\src\Microsoft.Agents.AI.AGUI\Shared\ChatResponseUpdateAGUIExtensions.cs dotnet\src\Microsoft.Agents.AI.AGUI\Shared\BaseEventJsonConverter.cs dotnet\tests\Microsoft.Agents.AI.AGUI.UnitTests\ChatResponseUpdateAGUIExtensionsTests.cs
git diff --check

Result: build succeeded with 0 warnings/errors; 4 targeted tests passed; format and diff checks passed.

Note: dotnet test with this .NET 10 SDK hits the Microsoft.Testing.Platform/VSTest transition error, so I used the built MTP test assembly directly for the targeted run.

[Yufeng He (he-yufeng)]

Rebased this branch onto current main and force-pushed with lease. Re-ran the focused AG-UI validation after the rebase: AGUI unit-test project build passed with 0 warnings/errors; the text START metadata test, StateDelta BaseEvent converter test, JSON Patch StateDelta emission test, and existing text-event metadata test all passed; dotnet format --verify-no-changes passed for the touched files; git diff --check passed.

[Yufeng He (he-yufeng)]

Merged current upstream/main into this branch and re-ran the focused AG-UI validation.

Validation:

dotnet build dotnet\tests\Microsoft.Agents.AI.AGUI.UnitTests\Microsoft.Agents.AI.AGUI.UnitTests.csproj --no-restore
dotnet dotnet\tests\Microsoft.Agents.AI.AGUI.UnitTests\bin\Debug\net10.0\Microsoft.Agents.AI.AGUI.UnitTests.dll --filter-method '*AsChatResponseUpdatesAsync_WithTextStartAdditionalProperties_PreservesAndMergesMetadataAsync' --filter-method '*BaseEventJsonConverter_WithStateDeltaEvent_DeserializesStateDeltaEvent' --filter-method '*AsAGUIEventStreamAsync_ConvertsDataContentWithJsonPatch_ToStateDeltaEventAsync' --filter-method '*AsChatResponseUpdatesAsync_WithTextEventAdditionalProperties_PreservesTextContentMetadataAsync' --no-progress
dotnet format dotnet\agent-framework-dotnet.slnx --verify-no-changes --no-restore --include dotnet\src\Microsoft.Agents.AI.AGUI\Shared\ChatResponseUpdateAGUIExtensions.cs dotnet\src\Microsoft.Agents.AI.AGUI\Shared\BaseEventJsonConverter.cs dotnet\tests\Microsoft.Agents.AI.AGUI.UnitTests\ChatResponseUpdateAGUIExtensionsTests.cs
git diff --check

Result: build passed with 0 warnings/errors, 4 targeted tests passed, format and diff checks passed.

[Evan Mattson (moonbox3)]

Yufeng He (@he-yufeng) please have a look at the conflicted file. Thanks.

[Yufeng He (he-yufeng)]

Resolved the current conflict in ChatResponseUpdateAGUIExtensions.cs and rebased onto latest microsoft:main.

The conflict was between the newer textMessageId fallback logic on main and this PR's START-event metadata preservation. I kept both: the start/end/content events still use textMessageId, and TextMessageStartEvent still receives copied TextContent.AdditionalProperties with AG-UI reserved fields filtered.

Validation:

dotnet build dotnet\tests\Microsoft.Agents.AI.AGUI.UnitTests\Microsoft.Agents.AI.AGUI.UnitTests.csproj --tl:off
# succeeded, 0 warnings, 0 errors

dotnet dotnet\tests\Microsoft.Agents.AI.AGUI.UnitTests\bin\Debug\net10.0\Microsoft.Agents.AI.AGUI.UnitTests.dll --filter-method '*AsChatResponseUpdatesAsync_WithTextStartAdditionalProperties_PreservesAndMergesMetadataAsync' --filter-method '*BaseEventJsonConverter_WithStateDeltaEvent_DeserializesStateDeltaEvent' --filter-method '*AsAGUIEventStreamAsync_ConvertsDataContentWithJsonPatch_ToStateDeltaEventAsync' --filter-method '*AsChatResponseUpdatesAsync_WithTextEventAdditionalProperties_PreservesTextContentMetadataAsync' --no-progress
# 4 passed

dotnet format dotnet\agent-framework-dotnet.slnx --verify-no-changes --no-restore --include dotnet\src\Microsoft.Agents.AI.AGUI\Shared\ChatResponseUpdateAGUIExtensions.cs dotnet\src\Microsoft.Agents.AI.AGUI\Shared\BaseEventJsonConverter.cs dotnet\tests\Microsoft.Agents.AI.AGUI.UnitTests\ChatResponseUpdateAGUIExtensionsTests.cs

git diff --check

[Yufeng He (he-yufeng)]

Rebased this branch onto current microsoft:main and pushed 614846a5.

There were no conflicts in the latest rebase; this just brings the AG-UI metadata patch back up to date with main.

Validation on Windows:

dotnet build dotnet\tests\Microsoft.Agents.AI.AGUI.UnitTests\Microsoft.Agents.AI.AGUI.UnitTests.csproj --tl:off
# succeeded, 0 warnings, 0 errors

dotnet dotnet\tests\Microsoft.Agents.AI.AGUI.UnitTests\bin\Debug\net10.0\Microsoft.Agents.AI.AGUI.UnitTests.dll --filter-method '*AsChatResponseUpdatesAsync_WithTextStartAdditionalProperties_PreservesAndMergesMetadataAsync' --filter-method '*BaseEventJsonConverter_WithStateDeltaEvent_DeserializesStateDeltaEvent' --filter-method '*AsAGUIEventStreamAsync_ConvertsDataContentWithJsonPatch_ToStateDeltaEventAsync' --filter-method '*AsChatResponseUpdatesAsync_WithTextEventAdditionalProperties_PreservesTextContentMetadataAsync' --no-progress
# 4 passed

dotnet format dotnet\agent-framework-dotnet.slnx --verify-no-changes --no-restore --include dotnet\src\Microsoft.Agents.AI.AGUI\Shared\ChatResponseUpdateAGUIExtensions.cs dotnet\src\Microsoft.Agents.AI.AGUI\Shared\BaseEventJsonConverter.cs dotnet\tests\Microsoft.Agents.AI.AGUI.UnitTests\ChatResponseUpdateAGUIExtensionsTests.cs
# exit 0; workspace load warning only

git diff --check
# passed

[Yufeng He (he-yufeng)]

One more main commit landed while I was updating the branch, so I rebased again and pushed 997ace53.

Current local check against the latest fetched upstream/main:

git rev-list --left-right --count HEAD...upstream/main
# 2 0

Validation after the second rebase:

dotnet build dotnet\tests\Microsoft.Agents.AI.AGUI.UnitTests\Microsoft.Agents.AI.AGUI.UnitTests.csproj --tl:off
# succeeded, 0 warnings, 0 errors

dotnet dotnet\tests\Microsoft.Agents.AI.AGUI.UnitTests\bin\Debug\net10.0\Microsoft.Agents.AI.AGUI.UnitTests.dll --filter-method '*AsChatResponseUpdatesAsync_WithTextStartAdditionalProperties_PreservesAndMergesMetadataAsync' --filter-method '*BaseEventJsonConverter_WithStateDeltaEvent_DeserializesStateDeltaEvent' --filter-method '*AsAGUIEventStreamAsync_ConvertsDataContentWithJsonPatch_ToStateDeltaEventAsync' --filter-method '*AsChatResponseUpdatesAsync_WithTextEventAdditionalProperties_PreservesTextContentMetadataAsync' --no-progress
# 4 passed

dotnet format dotnet\agent-framework-dotnet.slnx --verify-no-changes --no-restore --include dotnet\src\Microsoft.Agents.AI.AGUI\Shared\ChatResponseUpdateAGUIExtensions.cs dotnet\src\Microsoft.Agents.AI.AGUI\Shared\BaseEventJsonConverter.cs dotnet\tests\Microsoft.Agents.AI.AGUI.UnitTests\ChatResponseUpdateAGUIExtensionsTests.cs
# exit 0; workspace load warning only

git diff --check
# passed

[Yufeng He (he-yufeng)]

Gentle ping on this AG-UI metadata preservation fix. The branch has two approvals, the focused AG-UI validation passed after the last rebase, and current checks are green.

The patch still keeps reserved AG-UI protocol fields filtered while preserving user metadata through the event/content conversions. Happy to rebase again if maintainers want a fresher head before landing.

[Yufeng He (he-yufeng)]

Same story as the other AG-UI PRs: #6653 swapped the in-tree AG-UI abstractions (Shared/BaseEvent.cs, BaseEventJsonConverter.cs, ChatResponseUpdateAGUIExtensions.cs) for the external AG-UI C# SDK and deleted that directory, so this can no longer be rebased. Closing. Thanks Jacob Alber (@lokitoth) Evan Mattson (@moonbox3) for the reviews — the metadata-preservation behavior would need to move to the AGUI.Server SDK now, which I'll check.