Get Zoom Map

The continuous-zoom containment tree (system -> layer -> ... -> file).

The one endpoint in this module that is not a pure artifact passthrough: the zoom map has no artifact of its own (OSS derives it per request too), so this reads the curated architecture view plus per-file health and runs the same pure assembly OSS does. Both reads go through the byte-budgeted artifact service and nothing derived is retained, so the route adds no cache of its own.

The assembly is CPU-bound (hundreds of milliseconds on a few thousand files), so it runs off the event loop on the service's own single-thread executor — not the default pool, which artifact decoding shares (see zoom_map_service.build_zoom_map_async).