.NET: Align WorkflowOutputEvent streaming deserialization with SourceId to ExecutorId rename

[kshyju]

Motivation & Context

PR #3441 renamed WorkflowOutputEvent.SourceId to ExecutorId (keeping SourceId as an [Obsolete] + [JsonIgnore] alias), but the manual streaming deserialization in DeserializeEventByType was not updated. It still calls root.GetProperty("sourceId"), which throws a KeyNotFoundException at runtime because the serialized JSON contains "executorId".

This causes WatchStreamAsync to crash with an unhandled exception whenever the stream includes a WorkflowOutputEvent (e.g., when an executor calls YieldOutputAsync).

Description & Review Guide

• What are the major changes?
  Updated the WorkflowOutputEvent branch in DeserializeEventByType to read "executorId" from the JSON payload instead of "sourceId". Used variable name outputExecutorId to avoid shadowing the executorId variable declared in the ExecutorInvokedEvent/ExecutorCompletedEvent branches above.

• What is the impact of these changes?
  Fixes a runtime crash in WatchStreamAsync for any durable workflow that yields output. No behavioral change beyond fixing the deserialization to match the current property name.

• What do you want reviewers to focus on?
  Confirming there are no other references to the old "sourceId" JSON key in the durable task serialization/deserialization paths.

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.

[Copilot]

Pull request overview

Fixes a runtime crash in durable workflow streaming by aligning the manual WorkflowOutputEvent JSON deserialization with the post-#3441 rename from SourceId to ExecutorId.

Changes:

• Update DeserializeEventByType to read executorId for WorkflowOutputEvent deserialization.
• Add a unit test that validates WorkflowOutputEvent round-trips through WatchStreamAsync without throwing.

Reviewed changes

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

File	Description
dotnet/src/Microsoft.Agents.AI.DurableTask/Workflows/DurableStreamingWorkflowRun.cs	Updates the manual streaming deserialization path for WorkflowOutputEvent to match the new JSON key (executorId).
dotnet/tests/Microsoft.Agents.AI.DurableTask.UnitTests/Workflows/DurableStreamingWorkflowRunTests.cs	Adds coverage to ensure WorkflowOutputEvent can be streamed/deserialized correctly via WatchStreamAsync.

[github-actions]

Automated Code Review

Reviewers: 5 | Confidence: 94% | Result: All clear

Reviewed: Correctness, Security Reliability, Test Coverage, Failure Modes, Design Approach

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Automated review by kshyju's agents

[Copilot]

Pull request overview

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

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.

[github-actions]

Automated Code Review

Reviewers: 5 | Confidence: 94%

✓ Correctness

The fix is correct and well-tested. It replaces the crash-prone GetProperty("sourceId") call with TryGetProperty("executorId") and a fallback to TryGetProperty("sourceId"), matching the current WorkflowOutputEvent class where ExecutorId is the primary property (serialized as executorId) and SourceId is an [Obsolete] + [JsonIgnore] alias. The CHANGELOG entry follows the project convention with a PR link. Both the new-format and legacy-format deserialization paths are covered by tests. No correctness issues found.

✓ Security Reliability

The fix correctly replaces a crash-prone GetProperty("sourceId") call with a robust TryGetProperty fallback chain that handles both the new executorId and legacy sourceId JSON keys. The CHANGELOG is properly formatted with a PR link. Tests cover both the modern and legacy deserialization paths. No security or reliability issues are introduced by this change.

✓ Test Coverage

The PR has good test coverage for the fix. Two new tests exercise both the modern executorId JSON path and the legacy sourceId fallback path. Assertions are meaningful — they verify the deserialized ExecutorId, Data, and Tags properties. The only untested edge case is when neither key is present (defaults to empty string), but this is a minor defensive path for corrupted payloads and not worth blocking on. The pre-existing gap where tags are not deserialized in the manual path is not introduced by this PR.

✓ Failure Modes

The PR correctly fixes a runtime crash in WatchStreamAsync caused by the sourceId→executorId rename. The use of TryGetProperty with fallback is the right approach since the surrounding catch block only handles JsonException, not the KeyNotFoundException that GetProperty would throw for missing keys. Tests cover both the new and legacy deserialization paths. CHANGELOG entry matches project conventions. No new failure modes introduced.

✓ Design Approach

I found one design issue in the new WorkflowOutputEvent fallback: it preserves backward compatibility for sourceId, but it also changes malformed payload handling from "reject as unparsable" to "silently construct an event with an empty executor ID." That weakens the event contract and can hide corrupted stream data. I did not find other design-level issues in the diff.

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Automated review by kshyju's agents

[github-actions]

This fallback now silently accepts a malformed payload like {"data":"x"} and produces a WorkflowOutputEvent with an empty ExecutorId. That violates the documented invariant that ExecutorId is "The unique identifier of the executor that yielded this output." The surrounding caller already treats JsonException as an unparsable event (DurableStreamingWorkflowRun.cs:395-397), so the backward-compat path should still fail closed when neither key is present instead of manufacturing anonymous output event.

Suggested change

	: string.Empty;
	string outputExecutorId = root.TryGetProperty("executorId", out JsonElement execIdElem)
	? execIdElem.GetString() ?? string.Empty
	: root.TryGetProperty("sourceId", out JsonElement srcIdElem)
	? srcIdElem.GetString() ?? string.Empty
	: throw new JsonException("WorkflowOutputEvent is missing required executorId/sourceId.");