fix(streams): observe discarded materialized Task<Done>s to prevent daemon-unobserved crashes#998
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Aaronontheweb merged 3 commits intoMay 14, 2026
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…ved-task crashes Akka.Streams stages (Sink.ForEach via IgnoreSink, Source.Queue) create internal Task<Done> instances via TaskCompletionSource. Several code paths discarded those tasks (Keep.Left on Sink.ForEach; never calling WatchCompletionAsync on Source.Queue). On stream teardown the TCSes are faulted with AbruptTerminationException or StreamDetachedException; since .NET tracks "observed" per-Task, the discarded tasks fired TaskScheduler.UnobservedTaskException and surfaced as daemon-unobserved crash logs during hot reload and idle passivation. - SessionPipelineHandle.InitializeWithChannelAsync: Keep.Both + await both watch + sink tasks; wrap onStreamTerminated callback in try/catch. - SessionPipelineHandle.InitializeWithQueueAsync: Keep.Both + observe sink task; observe Source.Queue's WatchCompletionAsync task. - ChannelPipeline.CreateAsync: wrap inner Sink.ForEach with MapMaterializedValue + ContinueWith(OnlyOnFaulted) to observe the discarded foreach task. - RecordingSessionPipeline (test helper): same fix. - New SessionPipelineUnobservedTaskTests covers both observation patterns.
…elper Extract the MapMaterializedValue + ContinueWith pattern into StreamTaskObservation with an ObservingFault extension on Sink<TIn, Task<Done>>. Replaces four near-identical inline blocks across SessionPipelineHandle, ChannelPipeline, and RecordingSessionPipeline. Also drops the Keep.Both + dual-await dance in InitializeWithChannelAsync now that the sink's internal task is observed at sink-construction time, so ObserveTerminationAsync collapses back to a single await. Net 75 lines removed.
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Summary
daemon-unobservedcrash classes (AbruptTerminationException,StreamDetachedException) triggered during ActorSystem hot reload and idle passivation.IgnoreSinkbackingSink.ForEach,QueueSource._completion) create internalTaskCompletionSource<Done>instances that fault on teardown. Our code discarded those tasks viaKeep.Left/ never callingWatchCompletionAsync()..NETtracks "observed" per-Task, so the discarded tasks firedTaskScheduler.UnobservedTaskExceptionon the finalizer thread.RunContinuationsAsynchronouslywidened the observation window. Crash-log rate went from ~2 over 6 days pre-bump to 90+ over 17 days post-bump (~25× jump). Upstream issues filed: akkadotnet/akka.net#8209, #8210, #8211.Changes
Netclaw.Actors/Channels/StreamTaskObservation.cswith two helpers:ObserveSilently(Task)— fault-onlyContinueWiththat reads.Exception.Sink<TIn, Task<Done>>.ObservingFault()— extension wrappingMapMaterializedValueto swapTask<Done>forNotUsedafter attachingObserveSilently.SessionPipelineHandle.InitializeWithChannelAsync/InitializeWithQueueAsync: apply.ObservingFault()to the outputSink.ForEach; callObserveSilentlyonSource.Queue.WatchCompletionAsync(). Wrap theonStreamTerminatedcallback in try/catch.ChannelPipeline.CreateAsync: same.ObservingFault()on the inputSink.ForEach.RecordingSessionPipeline(test helper): same fix in both reactive and non-reactive branches.SessionPipelineUnobservedTaskTestscovers both observation patterns (Keep.Both+await-both andMapMaterializedValue+continuation).Test plan
dotnet test src/Netclaw.Actors.Tests— 1584/1584 passingdotnet test src/Netclaw.Daemon.Tests— 529/529 passingdotnet slopwatch analyze— 0 issues./scripts/Add-FileHeaders.ps1 -Verify— cleancrash-*.logfiles withAbruptTerminationException/StreamDetachedException.