Migrates the test-lib content authored alongside lib-core.maps v0.2.0
into its canonical role=test location. Covers packed-u32 GID encode/
decode round-trip, v1 to v2 schema upgrade, schema-v2 validation,
multi-layer load, multi-atlas resolution, per-layer tile lookup with
tile_at backwards-compat, gameplay queries (is_walkable, blocks_walk,
blocks_sight), layer iteration around the entity slot, and v1 JSON
auto-migration on load. 367 assertions total when run via the engine
test-libs harness.
New fixtures: maps/demo_v2.map.json (4x4 multi-layer with roof) and
assets/tiles/walls_tilemap.tilemap.json (second atlas with wall tiles).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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