fix: eliminate data race in SleeperTask context lifecycle

pkg/utils/sleeper_task.go

@@ -2,6 +2,7 @@ package utils
 
 import (
 	"context"
+	"time"
 
 	"github.com/smartcontractkit/chainlink-common/pkg/services"
 )
@@ -110,8 +111,7 @@ func (s *SleeperTask) WorkDone() <-chan struct{} {
 func (s *SleeperTask) workerLoop() {
 	defer close(s.chDone)
 
-	ctx, cancel := s.chStop.NewCtx()
-	defer cancel()
+	ctx := &stopChanCtx{ch: s.chStop}
 
 	for {
 		select {
@@ -124,6 +124,25 @@ func (s *SleeperTask) workerLoop() {
 	}
 }
 
+// stopChanCtx implements [context.Context] backed directly by a stop channel.
+// Unlike [services.StopChan.NewCtx], this does not spawn a goroutine to call
+// cancel(), avoiding a data race between context cancellation and concurrent
+// reflect-based reads (e.g. testify mock argument formatting).
+type stopChanCtx struct{ ch <-chan struct{} }
+
+func (c *stopChanCtx) Deadline() (time.Time, bool) { return time.Time{}, false }
+func (c *stopChanCtx) Done() <-chan struct{}        { return c.ch }
+func (c *stopChanCtx) Value(any) any                { return nil }
+
+func (c *stopChanCtx) Err() error {
+	select {
+	case <-c.ch:
+		return context.Canceled
+	default:
+		return nil
+	}
+}
+
 type sleeperTaskWorker struct {
 	name string
 	work func()

pkg/utils/sleeper_task_test.go

@@ -1,6 +1,9 @@
 package utils_test
 
 import (
+	"context"
+	"fmt"
+	"sync"
 	"testing"
 	"time"
 
@@ -72,6 +75,43 @@ func TestSleeperTask_WakeupPerformsWork(t *testing.T) {
 	require.NoError(t, sleeper.Stop())
 }
 
+// reflectWorker simulates the race scenario: Work() spawns goroutines that
+// read the context via fmt.Sprintf (like testify's mock.callString), while
+// Stop() concurrently triggers context cancellation.
+type reflectWorker struct {
+	wg sync.WaitGroup
+}
+
+func (w *reflectWorker) Name() string { return "ReflectWorker" }
+
+func (w *reflectWorker) Work(ctx context.Context) {
+	w.wg.Add(10)
+	for range 10 {
+		go func() {
+			defer w.wg.Done()
+			// Simulate testify's callString: fmt.Sprintf("%#v", ctx) reads context
+			// internals via reflect. With the old NewCtx()/CtxCancel pattern, cancel()
+			// fired concurrently, writing to context internals → DATA RACE.
+			_ = fmt.Sprintf("%#v", ctx)
+		}()
+	}
+	w.wg.Wait()
+}
+
+func TestSleeperTask_NoConcurrentContextRace(t *testing.T) {
+	t.Parallel()
+
+	// Run many iterations to increase chance of triggering a race.
+	for range 50 {
+		w := &reflectWorker{}
+		sleeper := utils.NewSleeperTaskCtx(w)
+		sleeper.WakeUp()
+		// Stop concurrently with Work — this closes chStop, which previously
+		// fired cancel() via a CtxCancel goroutine, racing with reflect reads.
+		require.NoError(t, sleeper.Stop())
+	}
+}
+
 type controllableWorker struct {
 	chanWorker
 	awaitWorkStarted chan struct{}