fix: complete target diagnostics and reset inspection

internal/apt/apt.go

@@ -82,6 +82,8 @@ type Adapter struct {
 	runner        Runner
 }
 
+var _ target.Diagnosable = (*Adapter)(nil)
+
 func New(configuration Configuration, files FileSystem, runner Runner) *Adapter {
 	defaults := DefaultConfiguration()
 	if configuration.DebianVersionFile == "" {
@@ -116,6 +118,32 @@ func (a *Adapter) Description() target.Description {
 
 func (a *Adapter) Confirmation(bool) string { return "" }
 
+// DiagnosticChecks observes the APT command, configuration schema, and current
+// filesystem authority without changing the overlay or effective settings.
+func (a *Adapter) DiagnosticChecks(ctx context.Context, _ *profile.Profile) []target.Check {
+	commandCheck := target.Check{Name: "required command", OK: true, Evidence: "apt-config is available"}
+	command, err := a.runner.LookPath("apt-config")
+	if err != nil {
+		commandCheck.OK = false
+		commandCheck.Evidence = "apt-config is unavailable: " + profile.RedactText(err.Error())
+	} else if _, err := a.runner.Output(ctx, command, "dump"); err != nil {
+		commandCheck.OK = false
+		commandCheck.Evidence = "apt-config dump failed: " + profile.RedactText(err.Error())
+	}
+	marker, markerErr := os.Stat(a.configuration.DebianVersionFile)
+	directory, directoryErr := os.Stat(a.configuration.ConfigDirectory)
+	schemaOK := markerErr == nil && marker.Mode().IsRegular() && directoryErr == nil && directory.IsDir()
+	schemaEvidence := "Debian marker and apt.conf.d configuration directory are present"
+	if !schemaOK {
+		schemaEvidence = profile.RedactText(fmt.Sprintf("Debian marker or apt.conf.d configuration directory is unusable: marker=%v directory=%v", markerErr, directoryErr))
+	}
+	return []target.Check{
+		commandCheck,
+		{Name: "configuration schema", OK: schemaOK, Evidence: schemaEvidence},
+		target.ReadOnlyWriteAuthority(a.configuration.OverlayFile),
+	}
+}
+
 func (a *Adapter) Availability(ctx context.Context) target.Availability {
 	marker, err := os.Stat(a.configuration.DebianVersionFile)
 	if err != nil || !marker.Mode().IsRegular() {