feat: consume manifest-driven native roads

.trellis/tasks/08-25-rc-p3-render-separation/research/debug-probe-evidence.md

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+# P3 Debug Probe Evidence
+
+Date: 2026-08-26
+
+A temporary, uncommitted compiler registry entry declared `debug_probe` as a
+`marking` layer using the existing `road_surface` material slot. Its generated
+GeoJSON reused the compiled road-surface collection only for this wiring test.
+No host source was changed.
+
+The compiler emitted 13 declared sources. Blender then generated
+`/private/tmp/p3-debug-probe.blend`; `SCENE_DONE` reported
+`"debug_probe": 30`. The Blender scene digest contains:
+
+```json
+{"name":"Road_debug_probe","vertices":274,"polygons":30}
+```
+
+The temporary registry entry was removed immediately after the proof. The
+standard v0.2.0 compiler was then rerun to restore the normal 12-source output.