Launch agent transport as goroutine

The agent depends on the transport to block and hold the program open.
Transports may block, but shouldn't be required to. This change ensures
the agent is self sustaining with a block and launches the transport in
its own goroutine.

Signed-off-by: Chris Doherty <chris.doherty4@gmail.com>

internal/agent/agent.go

@@ -3,6 +3,7 @@ package agent
 import (
 	"context"
 	"errors"
+	"fmt"
 
 	"github.com/go-logr/logr"
 	"github.com/tinkerbell/tink/internal/agent/event"
@@ -27,6 +28,7 @@ type Agent struct {
 	// Runtime is the container runtime used to execute workflow actions.
 	Runtime ContainerRuntime
 
+	// sem ensure we handle a single workflow at a time.
 	sem chan struct{}
 }
 
@@ -43,8 +45,7 @@ func (agent *Agent) Start(ctx context.Context) error {
 	}
 
 	if agent.Runtime == nil {
-		//nolint:stylecheck // Specifying field on data structure
-		return errors.New("Runtime field must be set before calling Start()")
+		return errors.New("agent.Runtime must be set before calling Start()")
 	}
 
 	agent.Log = agent.Log.WithValues("agent_id", agent.ID)
@@ -53,8 +54,19 @@ func (agent *Agent) Start(ctx context.Context) error {
 	agent.sem = make(chan struct{}, 1)
 	agent.sem <- struct{}{}
 
-	agent.Log.Info("Starting agent")
-	return agent.Transport.Start(ctx, agent.ID, agent)
+	// Launch the transport ensuring we can recover any errors.
+	transportErr := make(chan error, 1)
+	go func() {
+		agent.Log.Info("Starting agent")
+		transportErr <- agent.Transport.Start(ctx, agent.ID, agent)
+	}()
+
+	select {
+	case err := <-transportErr:
+		return fmt.Errorf("transport: %w", err)
+	case <-ctx.Done():
+		return ctx.Err()
+	}
 }
 
 // HandleWorkflow satisfies transport.