.NET: fix fan-in barrier checkpoint state

[Yufeng He (he-yufeng)]

Summary

Fixes #6372.

The in-process runner was checkpointing a runner-owned EdgeMap, while message delivery and fan-in buffering actually use the EdgeMap owned by InProcessRunnerContext. That meant a checkpoint taken after one side of a fan-in barrier had arrived could persist an empty edge state, then lose the buffered message on resume.

This changes checkpoint export/import to go through the live runner context edge map and adds a regression test that pauses with one fan-in input buffered, resumes, replies to the pending request, and verifies the barrier releases both pre-checkpoint and post-resume contributions.

Validation

• git diff --check
• dotnet run --project .\tests\Microsoft.Agents.AI.Workflows.UnitTests\Microsoft.Agents.AI.Workflows.UnitTests.csproj -f net10.0 -- --filter-method Microsoft.Agents.AI.Workflows.UnitTests.CheckpointResumeTests.Checkpoint_Resume_PreservesFanInBarrierBufferedMessagesAsync --no-progress
• dotnet run --project .\tests\Microsoft.Agents.AI.Workflows.UnitTests\Microsoft.Agents.AI.Workflows.UnitTests.csproj -f net10.0 -- --filter-class Microsoft.Agents.AI.Workflows.UnitTests.CheckpointResumeTests --no-progress
• dotnet build .\tests\Microsoft.Agents.AI.Workflows.UnitTests\Microsoft.Agents.AI.Workflows.UnitTests.csproj --no-restore --tl:off
• dotnet format .\src\Microsoft.Agents.AI.Workflows\Microsoft.Agents.AI.Workflows.csproj --verify-no-changes --no-restore --verbosity minimal
• dotnet format .\tests\Microsoft.Agents.AI.Workflows.UnitTests\Microsoft.Agents.AI.Workflows.UnitTests.csproj --verify-no-changes --no-restore --verbosity minimal

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Adds coverage and runtime support for preserving fan-in barrier buffered edge state across checkpoint/resume in the in-process workflow runner.

Changes:

• Added a new unit test that checkpoints with a partially satisfied fan-in barrier and verifies buffered contributions are released after resume.
• Exposed edge-state export/import on InProcessRunnerContext.
• Updated InProcessRunner to use RunContext for edge-state serialization during checkpoint/restore.

Reviewed changes

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

File	Description
dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/CheckpointResumeTests.cs	Adds a regression test and local executors/events to validate fan-in barrier buffering across resume.
dotnet/src/Microsoft.Agents.AI.Workflows/InProc/InProcessRunnerContext.cs	Adds context-level methods to export/import edge state with checkpoint lifecycle checks.
dotnet/src/Microsoft.Agents.AI.Workflows/InProc/InProcessRunner.cs	Routes checkpoint/restore edge-state handling through RunContext instead of a runner-owned EdgeMap.

[Yufeng He (he-yufeng)]

Rebased onto current main; no code changes beyond replaying the existing commit.

Validated locally on Windows with the focused checkpoint regression:

dotnet test --project ./tests/Microsoft.Agents.AI.Workflows.UnitTests/Microsoft.Agents.AI.Workflows.UnitTests.csproj -f net10.0 -c Debug -v Normal --report-xunit-trx --ignore-exit-code 8 --filter-method "*Checkpoint_Resume_PreservesFanInBarrierBufferedMessagesAsync"
dotnet test --project ./tests/Microsoft.Agents.AI.Workflows.UnitTests/Microsoft.Agents.AI.Workflows.UnitTests.csproj -f net472 -c Debug -v Normal --report-xunit-trx --ignore-exit-code 8 --filter-method "*Checkpoint_Resume_PreservesFanInBarrierBufferedMessagesAsync"
git diff --check upstream/main..HEAD

Both target frameworks passed the focused test (2 theory cases each).

[Yufeng He (he-yufeng)]

Rebased this branch onto current main and pushed head e79f94591.

Validation run locally from dotnet/:

• git diff --check upstream/main..HEAD -> passed
• dotnet build .\tests\Microsoft.Agents.AI.Workflows.UnitTests\Microsoft.Agents.AI.Workflows.UnitTests.csproj --no-restore --tl:off -> passed, 0 warnings/errors
• dotnet run --project .\tests\Microsoft.Agents.AI.Workflows.UnitTests\Microsoft.Agents.AI.Workflows.UnitTests.csproj -f net10.0 -- --filter-method Microsoft.Agents.AI.Workflows.UnitTests.CheckpointResumeTests.Checkpoint_Resume_PreservesFanInBarrierBufferedMessagesAsync --no-progress -> passed, 2 tests
• dotnet run --project .\tests\Microsoft.Agents.AI.Workflows.UnitTests\Microsoft.Agents.AI.Workflows.UnitTests.csproj -f net472 -- --filter-method Microsoft.Agents.AI.Workflows.UnitTests.CheckpointResumeTests.Checkpoint_Resume_PreservesFanInBarrierBufferedMessagesAsync --no-progress -> passed, 2 tests