Spacetime: free analytic render worker count

src/spacetime.h

@@ -38,6 +38,10 @@ typedef struct {
                    MetricData *metric);
   SpacetimeRayStatus (*classify_slab)(const MetricSlab *slab, double t,
                                       const double x[3]);
+  /* Analytic backends have negligible per-ray metric state.  A numerical
+   * backend must opt in once its metric slabs and evaluator workspaces need
+   * to reserve memory alongside the private HDR render buffers. */
+  int limit_render_workers_by_memory;
   void (*destroy)(SpacetimeSource *source);
 } SpacetimeOps;
 
@@ -65,5 +69,6 @@ int spacetime_slab_eval(const MetricSlab *slab, double t, const double x[3],
                         MetricData *metric);
 SpacetimeRayStatus spacetime_slab_classify(const MetricSlab *slab, double t,
                                            const double x[3]);
+int spacetime_limits_render_workers_by_memory(const SpacetimeSource *source);
 
 #endif