Preserve publish queue timestamp ordering

[Copilot]

Proposed changes

The master378 publish timer reset timestamps for already-ready subscriptions, breaking oldest-first ordering among equal-priority subscriptions.

• Restore the ready-subscription guard.
• Recheck readiness under the queue lock to prevent concurrent timestamp resets.
• Replace invalid requeue coverage with a deterministic ordering regression test.

Related Issues

Types of changes

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• Bugfix (non-breaking change which fixes an issue)
• Enhancement (non-breaking change which adds functionality)
• Test enhancement (non-breaking change to increase test coverage)
• Breaking change (fix or feature that would cause existing functionality to not work as expected, requires version increase of Nuget packages)
• Documentation Update (if none of the other choices apply)

Checklist

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• I fixed all failing tests in the CI pipelines.
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• I have added tests that prove my fix is effective or that my feature works and increased code coverage.
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Further comments

Retains the single-lock lost-wakeup correction from the preceding change while preserving subscription scheduling timestamps.

• Fixes Monitored item notifications stop after SecureChannel token renewal in Kubernetes after upgrading from OPC UA .NET Standard 1.5.376 to 1.5.378 #3997

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1 out of 2 committers have signed the CLA.

✅ marcschier
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[Copilot]

Pull request overview

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Fixes a publish-queue regression where the publish timer could reset timestamps for already-ready subscriptions, breaking oldest-first ordering among equal-priority subscriptions.

Changes:

• Reinstate a guard to avoid touching subscriptions already marked ReadyToPublish.
• Recheck readiness under m_lock to avoid concurrent timestamp resets while assigning to requests.
• Replace the prior requeue/wakeup test with a new regression test focused on timestamp-based ordering.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

File	Description
Tests/Opc.Ua.Server.Tests/SessionPublishQueueRaceTests.cs	Renames/reworks the test to validate timestamp ordering behavior for ready subscriptions.
Libraries/Opc.Ua.Server/Subscription/SessionPublishQueue.cs	Adds readiness guards (outside and inside lock) to prevent timestamp/order corruption.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 60.16%. Comparing base (7e8f9e5) to head (ccbbfb5).
⚠️ Report is 1 commits behind head on master378.

Additional details and impacted files

@@              Coverage Diff              @@
##           master378    #4084      +/-   ##
=============================================
- Coverage      60.17%   60.16%   -0.01%     
=============================================
  Files            378      378              
  Lines          79070    79066       -4     
  Branches       13837    13837              
=============================================
- Hits           47577    47569       -8     
+ Misses         27080    27072       -8     
- Partials        4413     4425      +12     

Files with missing lines	Coverage Δ
.../Opc.Ua.Server/Subscription/SessionPublishQueue.cs	75.20% <100.00%> (-1.21%)	⬇️

... and 20 files with indirect coverage changes

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[mrsuciu]

@marcschier I think additional check is needed, see comment on code.