Add structured daemon lifecycle logs

VM start, image build, and network/setup failures were hard to diagnose because bangerd emitted almost no lifecycle logs and the Firecracker SDK logger was discarded. This adds a daemon-wide JSON logger with configurable log level so failures leave breadcrumbs instead of only side effects.

Log the main daemon and VM lifecycle stages, preserve raw Firecracker and image-build helper output in dedicated files, and include those log paths in daemon status and returned errors. Bridge SDK logrus output into the daemon logger at debug level so low-level Firecracker diagnostics are available without making normal info logs unreadable.

Validation: go test ./... and make build. Left unrelated worktree changes out of this commit, including internal/api/types.go, the deleted shell scripts, and my-rootfs.ext4.

internal/firecracker/client.go

@@ -3,6 +3,7 @@ package firecracker
 import (
 	"context"
 	"io"
+	"log/slog"
 	"os"
 	"os/exec"
 	"strings"
@@ -27,6 +28,7 @@ type MachineConfig struct {
 	TapDevice       string
 	VCPUCount       int
 	MemoryMiB       int
+	Logger          *slog.Logger
 }
 
 type Machine struct {
@@ -50,7 +52,7 @@ func NewMachine(ctx context.Context, cfg MachineConfig) (*Machine, error) {
 		ctx,
 		buildConfig(cfg),
 		sdk.WithProcessRunner(cmd),
-		sdk.WithLogger(newLogger()),
+		sdk.WithLogger(newLogger(cfg.Logger)),
 	)
 	if err != nil {
 		if logFile != nil {
@@ -80,8 +82,8 @@ func (m *Machine) PID() (int, error) {
 	return m.machine.PID()
 }
 
-func New(apiSock string) *Client {
-	return &Client{client: sdk.NewClient(apiSock, newLogger(), false)}
+func New(apiSock string, logger *slog.Logger) *Client {
+	return &Client{client: sdk.NewClient(apiSock, newLogger(logger), false)}
 }
 
 func (c *Client) SendCtrlAltDel(ctx context.Context) error {
@@ -150,12 +152,44 @@ func shellQuote(value string) string {
 	return "'" + strings.ReplaceAll(value, "'", `'"'"'`) + "'"
 }
 
-func newLogger() *logrus.Entry {
+func newLogger(base *slog.Logger) *logrus.Entry {
 	logger := logrus.New()
 	logger.SetOutput(io.Discard)
+	logger.SetLevel(logrus.DebugLevel)
+	logger.AddHook(slogHook{logger: base})
 	return logrus.NewEntry(logger)
 }
 
+type slogHook struct {
+	logger *slog.Logger
+}
+
+func (h slogHook) Levels() []logrus.Level {
+	return logrus.AllLevels
+}
+
+func (h slogHook) Fire(entry *logrus.Entry) error {
+	if h.logger == nil {
+		return nil
+	}
+	level := slog.LevelDebug
+	switch entry.Level {
+	case logrus.PanicLevel, logrus.FatalLevel, logrus.ErrorLevel:
+		level = slog.LevelError
+	case logrus.WarnLevel:
+		level = slog.LevelWarn
+	default:
+		level = slog.LevelDebug
+	}
+	attrs := make([]any, 0, len(entry.Data)*2+2)
+	attrs = append(attrs, "component", "firecracker_sdk")
+	for key, value := range entry.Data {
+		attrs = append(attrs, key, value)
+	}
+	h.logger.Log(context.Background(), level, entry.Message, attrs...)
+	return nil
+}
+
 func (m *Machine) closeLog() {
 	m.closeOnce.Do(func() {
 		if m.logFile != nil {

internal/firecracker/client_test.go

@@ -1,7 +1,10 @@
 package firecracker
 
 import (
+	"bytes"
 	"context"
+	"log/slog"
+	"strings"
 	"testing"
 )
 
@@ -76,3 +79,34 @@ func TestBuildProcessRunnerUsesSudoWrapper(t *testing.T) {
 		t.Fatalf("script = %q, want %q", cmd.Args[4], want)
 	}
 }
+
+func TestSDKLoggerBridgeEmitsStructuredDebugLogs(t *testing.T) {
+	var buf bytes.Buffer
+	logger := slog.New(slog.NewJSONHandler(&buf, &slog.HandlerOptions{Level: slog.LevelDebug}))
+
+	entry := newLogger(logger)
+	entry.WithField("vm_id", "vm-1").Info("sdk ready")
+
+	output := buf.String()
+	if !strings.Contains(output, `"component":"firecracker_sdk"`) {
+		t.Fatalf("output = %q, want firecracker_sdk component", output)
+	}
+	if !strings.Contains(output, `"vm_id":"vm-1"`) {
+		t.Fatalf("output = %q, want vm_id field", output)
+	}
+	if !strings.Contains(output, `"msg":"sdk ready"`) {
+		t.Fatalf("output = %q, want sdk message", output)
+	}
+}
+
+func TestSDKLoggerBridgeSuppressesDebugAtInfoLevel(t *testing.T) {
+	var buf bytes.Buffer
+	logger := slog.New(slog.NewJSONHandler(&buf, &slog.HandlerOptions{Level: slog.LevelInfo}))
+
+	entry := newLogger(logger)
+	entry.Info("sdk hidden at info")
+
+	if buf.Len() != 0 {
+		t.Fatalf("expected info-level logger to suppress sdk debug chatter, got %q", buf.String())
+	}
+}