🐛 subprocess Make sure that cancellation can't enter deadlock (#681)

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### Description

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Make sure that cancellation can't enter deadlock

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Author: joshjennings98

changes/20250818160732.bugfix

@@ -0,0 +1 @@
+:bug: `subprocess` Make sure that cancellation can't enter deadlock

utils/subprocess/monitoring.go

@@ -34,7 +34,16 @@ func newSubprocessMonitoring(parentCtx context.Context) *subprocessMonitoring {
 
 // CancelSubprocess interrupts an on-going process.
 func (s *subprocessMonitoring) CancelSubprocess() {
-	s.monitoringStopping.Store(true)
+	// Ensure we only ever run the cancel-store once and prevent the following deadlocks:
+	// 1. Some functions like Execute() do defer s.Cancel()
+	// 2. This calls subprocessMonitoring.CancelSubprocess() which calls cancelStore.Cancel() (acquiring mutex)
+	// 3. That Cancel() calls the context cancel func, which closes ProcessContext().Done()
+	// 4. The runProcessMonitoring blocks on ctx<-Done() and calls m.CancelSubprocess() again
+	// 5. This tries to run cancelStore.Cancel() a second time while the first Cancel() is still executing
+	// 6. go-deadlock detects deadlock
+	if s.monitoringStopping.Swap(true) {
+		return
+	}
 	s.cancelStore.Cancel()
 }