[Failing Test]: Flink 1.20 portable DataSet ValidatesRunner tests hang #40645

What happened?

Flink 1.20 portable DataSet ValidatesRunner jobs were hanging: pipelines stayed RUNNING until waitUntilFinish hit the 20 min timeout. Already happening on master.

Examples that hung:

• CombineTest$WindowingTests.testWindowedCombineGloballyAsSingletonView
• FlattenTest.testFlattenPCollections
• MapViewTest.testMapSideInput
• ParDoTest$MultipleInputsAndOutputTests.testSameSideInputReadTwice
• ParDoTest$TimerTests.testEventTimeTimerBounded
• SplittableDoFnTest.testWindowedSideInputBounded
• ViewTest.testEmptyListSideInput

https://github.com/apache/beam/actions/runs/38961839107/job/117178555850

Root cause was portable stage contexts sticking around across jobs in the same JVM. Fixed in #40632 (per job cleanup in FlinkExecutableStageContextFactory + portable VR parallelThreads=1).

Issue Failure

Failure: Test is continually failing

Issue Priority

Priority: 1 (unhealthy code / failing or flaky postcommit so we cannot be sure the product is healthy)

Issue Components

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