Report renderer progress and detect stalled jobs

shared/processing-progress.ts

@@ -0,0 +1,21 @@
+export type ProcessingJob = {
+  state: string;
+  progress: number;
+  error: string | null;
+  updated_at: string;
+  lease_until: string | null;
+};
+
+// Stage ranges describe completed work, never an estimate of remaining time.
+export function processingStage(progress: number) {
+  if (progress < 20) return "Downloading and checking the export";
+  if (progress < 25) return "Reading the terrain snapshot";
+  if (progress < 30) return "Indexing terrain blocks";
+  if (progress < 35) return "Loading block models and textures";
+  if (progress < 55) return "Building terrain geometry";
+  if (progress < 60) return "Preparing the scene";
+  if (progress < 85) return "Rendering panorama faces";
+  if (progress < 90) return "Rendering the surface map";
+  if (progress < 100) return "Saving processed images";
+  return "Processing complete";
+}