fix(supervisor): reset the request counter on a failed relaunch

restart() reset reqCounter only after a successful Launch, so a failed
one left it at the limit. maybeRestartAfterTask then re-fired on every
subsequent task, producing back-to-back restarts and, with planned
restarts now reporting healthy, a node that keeps restarting while
claiming health.

Reset on the attempt instead. A process that will not start is recovered
by ensureHealthy, which restarts synchronously and reports the failure.

pkg/gotenberg/supervisor.go

@@ -244,12 +244,18 @@ func (s *processSupervisor) restart() error {
 		s.logger.WarnContext(context.Background(), fmt.Sprintf("stop process before restart: %s", err))
 	}
 
+	// Reset the counter on the attempt, not on its outcome. Leaving it at the
+	// limit after a failed launch re-triggers maybeRestartAfterTask on every
+	// subsequent task, producing back-to-back restarts. Recovering a process
+	// that will not start is ensureHealthy's job: it restarts synchronously
+	// before running a task, and reports the failure to the caller.
+	s.reqCounter.Store(0)
+
 	err = s.Launch()
 	if err != nil {
 		return fmt.Errorf("restart process: %w", err)
 	}
 
-	s.reqCounter.Store(0)
 	s.restartsCounter.Add(1)
 	s.logger.DebugContext(context.Background(), "process successfully restarted")
 

pkg/gotenberg/supervisor_test.go

@@ -160,6 +160,41 @@ func TestProcessSupervisor_restart(t *testing.T) {
 	}
 }
 
+// TestProcessSupervisor_restart_ResetsCounterOnFailedLaunch verifies that a
+// restart whose launch fails still clears the request counter. Leaving it at
+// the limit makes maybeRestartAfterTask re-fire on every subsequent task.
+func TestProcessSupervisor_restart_ResetsCounterOnFailedLaunch(t *testing.T) {
+	logger := slog.New(slog.DiscardHandler)
+
+	const maxReqLimit = 5
+
+	process := &ProcessMock{
+		StartMock:   func(_ *slog.Logger) error { return errors.New("start error") },
+		StopMock:    func(_ *slog.Logger) error { return nil },
+		HealthyMock: func(_ *slog.Logger) bool { return true },
+	}
+
+	ps := NewProcessSupervisor(logger, "test", process, maxReqLimit, 0, 1, 0).(*processSupervisor)
+	ps.reqCounter.Store(maxReqLimit)
+
+	err := ps.restart()
+	if err == nil {
+		t.Fatal("expected error but got none")
+	}
+
+	if got := ps.reqCounter.Load(); got != 0 {
+		t.Fatalf("expected the request counter to be reset but got %d", got)
+	}
+
+	if got := ps.restartsCounter.Load(); got != 0 {
+		t.Fatalf("expected the restarts counter to stay at 0 but got %d", got)
+	}
+
+	if ps.maybeRestartAfterTask(logger) {
+		t.Fatal("expected no further eager restart to be triggered")
+	}
+}
+
 func TestProcessSupervisor_Healthy(t *testing.T) {
 	for _, tc := range []struct {
 		scenario                string