fix: cleanup zombie tasks

[warcholjakub]

Fixes #1275

[Copilot]

Pull request overview

Adds periodic cleanup of stale queued tasks in the balancer so dispatchers don’t keep tracking tasks indefinitely when they become “stuck”.

Changes:

• Add cleanUpStaleTasks(maxAge) to Server and propagate it through SBT / Scala-CLI load balancers.
• Introduce a CleanUpStaleTasks message handled by both dispatchers to prune old mailbox entries.
• Schedule periodic cleanup from DispatchActor.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
balancer/src/main/scala/org/scastie/balancer/Server.scala	Adds mailbox pruning based on task timestamp age.
balancer/src/main/scala/org/scastie/balancer/ScalaCliLoadBalancer.scala	Propagates stale-task cleanup across Scala-CLI servers.
balancer/src/main/scala/org/scastie/balancer/ScalaCliDispatcher.scala	Handles cleanup message and updates balancer state/logging.
balancer/src/main/scala/org/scastie/balancer/SbtLoadBalancer.scala	Propagates stale-task cleanup across SBT servers.
balancer/src/main/scala/org/scastie/balancer/SbtDispatcher.scala	Handles cleanup message and updates balancer state/logging.
balancer/src/main/scala/org/scastie/balancer/DispatchActor.scala	Defines cleanup message and schedules periodic cleanup.

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[Copilot]

Pull request overview

Adds periodic “stale task” cleanup to the balancer so that server mailboxes don’t stay artificially busy forever when tasks stop progressing, with configuration and unit tests around the cleanup logic.

Changes:

• Add cleanUpStaleTasks(maxAge) to Server, SbtLoadBalancer, and ScalaCliLoadBalancer.
• Schedule and handle a new CleanUpStaleTasks message in DispatchActor, SbtDispatcher, and ScalaCliDispatcher.
• Introduce stale-task-max-age config (default 2m) and add tests validating cleanup behavior.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
balancer/src/main/scala/org/scastie/balancer/Server.scala	Adds per-server mailbox cleanup based on task age.
balancer/src/main/scala/org/scastie/balancer/SbtLoadBalancer.scala	Propagates cleanup across SBT servers.
balancer/src/main/scala/org/scastie/balancer/ScalaCliLoadBalancer.scala	Propagates cleanup across Scala-CLI servers.
balancer/src/main/scala/org/scastie/balancer/SbtDispatcher.scala	Handles cleanup message and updates balancer/state reporting.
balancer/src/main/scala/org/scastie/balancer/ScalaCliDispatcher.scala	Handles cleanup message and updates balancer/state reporting.
balancer/src/main/scala/org/scastie/balancer/DispatchActor.scala	Schedules periodic cleanup + ping, and cancels schedules on stop.
balancer/src/main/resources/reference.conf	Adds stale-task-max-age default.
balancer/src/test/scala/org/scastie/balancer/LoadBalancerTest.scala	Adds unit tests for cleanup behavior on Server and both balancers.

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[Copilot]

Pull request overview

This PR introduces stale-task tracking/cleanup in the balancer layer to prevent long-running or “stuck” tasks from indefinitely occupying server mailboxes, and wires periodic cleanup into the dispatch lifecycle.

Changes:

• Extend Task with lastSeen and add APIs to refresh it and to purge stale tasks into history.
• Add cleanUpStaleTasks / refreshTaskLastSeen propagation on both SBT and Scala-CLI load balancers, and refresh lastSeen on incoming progress updates.
• Schedule periodic cleanup via DispatchActor, configurable via stale-task-max-age in reference.conf, and add tests for the new cleanup behavior.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
balancer/src/main/scala/org/scastie/balancer/Server.scala	Adds lastSeen to tasks plus server-level refresh/cleanup logic.
balancer/src/main/scala/org/scastie/balancer/SbtLoadBalancer.scala	Adds refresh/cleanup propagation across SBT servers.
balancer/src/main/scala/org/scastie/balancer/ScalaCliLoadBalancer.scala	Adds refresh/cleanup propagation across Scala-CLI servers.
balancer/src/main/scala/org/scastie/balancer/SbtDispatcher.scala	Refreshes task lastSeen on progress and handles periodic cleanup/logging.
balancer/src/main/scala/org/scastie/balancer/ScalaCliDispatcher.scala	Refreshes task lastSeen on progress and handles periodic cleanup/logging.
balancer/src/main/scala/org/scastie/balancer/DispatchActor.scala	Introduces scheduled periodic cleanup (and refactors ping scheduling/cancellation).
balancer/src/main/resources/reference.conf	Adds stale-task-max-age configuration setting.
balancer/src/test/scala/org/scastie/balancer/LoadBalancerTest.scala	Adds unit tests covering stale cleanup + lastSeen refresh.

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[Copilot]

Pull request overview

This PR addresses “zombie” (stuck/stale) tasks in the balancer—particularly impacting SBT runners—by tracking task liveness and periodically cleaning up tasks that have not been “seen” recently.

Changes:

• Add lastSeen tracking to Task plus APIs to refresh and clean up stale tasks at the Server level.
• Propagate refreshTaskLastSeen / cleanUpStaleTasks across SBT and Scala CLI load balancers and dispatchers, and schedule cleanup from DispatchActor.
• Introduce stale-task-max-age configuration (default 2m) and add unit tests for stale-task cleanup behavior.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
balancer/src/test/scala/org/scastie/balancer/LoadBalancerTest.scala	Adds tests for server and load balancer stale-task cleanup and lastSeen refresh behavior.
balancer/src/main/scala/org/scastie/balancer/Server.scala	Extends Task with lastSeen; implements per-server refresh and cleanup of stale tasks.
balancer/src/main/scala/org/scastie/balancer/ScalaCliLoadBalancer.scala	Adds balancer-level propagation for task lastSeen refresh and stale cleanup.
balancer/src/main/scala/org/scastie/balancer/ScalaCliDispatcher.scala	Refreshes task lastSeen on progress updates and handles scheduled stale cleanup + logging.
balancer/src/main/scala/org/scastie/balancer/SbtLoadBalancer.scala	Adds balancer-level propagation for task lastSeen refresh and stale cleanup.
balancer/src/main/scala/org/scastie/balancer/SbtDispatcher.scala	Refreshes task lastSeen on progress updates and handles scheduled stale cleanup + logging.
balancer/src/main/scala/org/scastie/balancer/DispatchActor.scala	Schedules periodic Ping and CleanUpStaleTasks, and cancels schedules on stop.
balancer/src/main/resources/reference.conf	Adds stale-task-max-age default configuration.

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[Copilot]

Pull request overview

This PR addresses issue #1275 by adding a “stale task” tracking mechanism in the balancer so tasks that stop reporting progress don’t remain indefinitely in runner status (i.e., “zombie tasks”), with periodic cleanup driven by the dispatch layer.

Changes:

• Extend Task with a lastSeen timestamp and add APIs to refresh it and to clean up stale tasks into server history.
• Add scheduled CleanUpStaleTasks propagation from DispatchActor to both SBT and Scala CLI dispatchers/load balancers.
• Add configuration for staleness threshold (stale-task-max-age) and unit tests covering cleanup/refresh behavior.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
balancer/src/main/scala/org/scastie/balancer/Server.scala	Adds lastSeen, refreshTaskLastSeen, and cleanUpStaleTasks to support stale task eviction.
balancer/src/main/scala/org/scastie/balancer/SbtLoadBalancer.scala	Propagates refresh/cleanup across servers for SBT.
balancer/src/main/scala/org/scastie/balancer/ScalaCliLoadBalancer.scala	Propagates refresh/cleanup across servers for Scala CLI.
balancer/src/main/scala/org/scastie/balancer/SbtDispatcher.scala	Refreshes lastSeen on progress and performs periodic stale cleanup with status updates.
balancer/src/main/scala/org/scastie/balancer/ScalaCliDispatcher.scala	Refreshes lastSeen on progress and performs periodic stale cleanup with status updates.
balancer/src/main/scala/org/scastie/balancer/DispatchActor.scala	Schedules periodic cleanup and forwards cleanup messages to both dispatchers; cancels schedules on stop.
balancer/src/main/resources/reference.conf	Introduces stale-task-max-age default configuration.
balancer/src/test/scala/org/scastie/balancer/LoadBalancerTest.scala	Adds tests validating cleanup/refresh semantics and propagation across load balancers.

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