Episode: Quad-sphere per-patch subdivision

EPISODE-GOAL

Replace the spherical detail patch with quad-sphere per-patch subdivision, so zoomed views subdivide each face patch instead of fetching a flat equirectangular window.

EPISODE-PHASE

phase 2

EPISODE-ACCEPTANCE

• Does a zoomed view subdivide the underlying sphere geometry per patch (quad-sphere style) rather than overlaying a single flat detail patch?
• Do the subdivisions stay consistent with the tile pyramid (each level maps to a pyramid zoom)?
• Does the viewport keep a bounded polygon budget while zoomed (no unbounded subdivision)?
• Is the whole change reviewable in one sitting?

EPISODE-RISKS

• Does per-patch subdivision interact correctly with the existing lon/lat UV convention (remapped in the base sphere)?
• Can the tile fetch logic be shared between the flat patch and the subdivided patches, or does it need a rewrite?

EPISODE-TASKS

• Design the quad-sphere patch subdivision scheme (levels ↔︎ pyramid zoom).
• Implement subdivision in site.in/globe.js.
• Reuse/extend the on-demand tile fetch for subdivided patches.
• Add a bounded-budget test for zoomed subdivision.
• Verify in headless Chrome: zoom to a region, check patch subdivision and tile coverage.

EPISODE-OUTPUT

Report the subdivision scheme, the changed files, and the headless-Chrome verification result.

EPISODE-FILES

• site.in/globe.js — existing
• site.in/globe.txt — existing
• scripts/etopo-tiles-build.sh — existing (if tile scheme changes)
• tests/ — new test for the subdivision budget

EPISODE-BRANCH

llm/episode-03