feat: publish durable queue and spool gauges

cmd/rvbox/main.go

@@ -180,6 +180,7 @@ func runClientDaemon(ctx context.Context, configPath string, diagnostics io.Writ
 		return fmt.Errorf("open client durable state: %w", err)
 	}
 	defer state.Close()
+	go publishClientTelemetry(ctx, state, health)
 	if diagnostics != nil {
 		_, _ = fmt.Fprintf(diagnostics, "rvbox client service initialized for %s\n", configured.Client.ServerURL)
 	}
@@ -250,6 +251,27 @@ func runClientDaemon(ctx context.Context, configPath string, diagnostics io.Writ
 	return nil
 }
 
+func publishClientTelemetry(ctx context.Context, state *spool.Store, health *observability.Health) {
+	ticker := time.NewTicker(10 * time.Second)
+	defer ticker.Stop()
+	for {
+		sampleContext, cancel := context.WithTimeout(ctx, time.Second)
+		telemetry, err := state.Telemetry(sampleContext)
+		cancel()
+		if err != nil {
+			health.Inc("telemetry_read_failure")
+		} else {
+			health.SetGauge("queue_depth", float64(telemetry.QueuedCommands))
+			health.SetGauge("client_spool_bytes", float64(telemetry.ChargedBytes))
+		}
+		select {
+		case <-ctx.Done():
+			return
+		case <-ticker.C:
+		}
+	}
+}
+
 func clientJobProfiles(profiles config.Profiles) map[string]clientwindows.JobProfile {
 	return map[string]clientwindows.JobProfile{
 		rvboxv1.ExecutionProfile_EXECUTION_PROFILE_LIGHT.String():       toJobProfile(profiles.Light),