docs(README): bump header 0.2.0 -> 0.5.4 + add v0.3-0.5.4 API summary

Adds schema-version table, v3 painting model (vertex grid + any-corner
rule + blob-14 SLOT_LOOKUP + override sublayer), and a per-version
summary of APIs added between 0.3.0 and 0.5.4. Original v0.2.0 entries
remain in their existing layout below the new summary.

README.md

@@ -1,11 +1,35 @@
 # lib-core.maps
 
-Single tile-grid map implementation. Loads JSON map + tilemap files, registers maps by id, and provides tile-fetch + walkability + size queries with current-map sugar.
+Multi-layer tile-grid map implementation with vertex-painted autotile
+(blob-14), sparse per-cell overrides, packed-u32 GID legacy path, atlas
+loading + UV resolution, walkability + sight-blocking queries, and a
+v3 multi-layer render pipeline with opaque-ceiling cache.
 
-**Version:** 0.2.0  
+**Version:** 0.5.4
 **Lib-ID:** lib-core.maps
 **Requires:** (none)
-**Tags:** maps, tile-grid, walkability, tilemap
+**Tags:** maps, tile-grid, multi-layer, vertex-painting, autotile, blob-14, override, walkability, tilemap
+
+## Schema versions
+
+| Version | Highlights |
+|---|---|
+| v1 | Single-layer `tiles[]` + tilemap path. Loaded but auto-upgraded to v2 on `maps.load`. |
+| v2 | Multi-atlas + multi-layer with packed-u32 GIDs (atlas_idx + tile_id + rotation). `set_cell_gid`, `save_to_disk`. |
+| v3 | Per-layer `material` (atlas-alias), optional `vertices` ((W+1)·(H+1) grid), optional `overrides` ({"x:y": int OR {slot, rot, flip}}). Renderer derives slot/rot/flip from neighbour-bitmask blob-gating; overrides force-place specific orientations. |
+
+## Painting model (v3 autotile)
+
+- **Vertex grid**: (W+1)·(H+1) cells. Any-corner rule: cell (x,y) is
+  material iff any of its 4 corner vertices is painted.
+- **Blob-gating + SLOT_LOOKUP**: each material cell's 8-bit
+  neighbour-bitmask (clockwise from N) is blob-gated (diagonals zeroed
+  unless both adjacent cardinals are set), then mapped to one of 14
+  canonical slots × {0,1,2,3} rotation × {0,1} flip via a D4-orbit
+  table. 47 distinct gated bitmasks total.
+- **Override sublayer**: sparse `{"x:y": slot}` or `{"x:y": {slot, rot,
+  flip}}`. Takes precedence over the bitmask-derived slot AND forces
+  material-presence on the cell.
 
 ## Topology
 
@@ -20,6 +44,51 @@ graph LR
 
 ## API
 
+> **Note:** the API section below was authored against v0.2.0 and is
+> being progressively updated. Entries marked `[v0.x added]` are the
+> additions since 0.2.0. See `init.lua` source for the full surface.
+
+### APIs added v0.3.0 — v0.5.4 (summary)
+
+- **v0.3.0** — atlas-baker integration: `load_textures(asset_aliases)`
+  rewrite for M.2 atlas format; height-field API; atlas-bootstrap
+  stub when tilemap JSON missing.
+- **v0.4.0** — write-APIs for editors / procedural-gen:
+  - `set_cell_gid(layer_name, x, y, gid, map_id?)`
+  - `set_roof(x, y, value, map_id?)`
+  - `save_to_disk(map_id, path)`
+- **v0.5.0a-e** — schema-v3 multi-layer terrain stack:
+  - 8 layer slots (`foundation`, `subsurface`, `surface`, `topsurface`,
+    `lower_wall`, `wall`, `upper_wall`, `canopy`)
+  - `LAYER_Z` + `LAYER_ORDER_TOP_DOWN` constants
+  - Vertex-painted autotile renderer (any-corner + blob-14 SLOT_LOOKUP)
+  - Empty-layer + opaque-ceiling caches for render-opt
+- **v0.5.0d** — sparse override sublayer:
+  - `set_override(layer_name, x, y, slot_or_entry, map_id?)`
+  - `clear_override(layer_name, x, y, map_id?)`
+  - `get_override(layer_name, x, y, map_id?)`
+- **v0.5.1** — override-entry format extension to `{slot, rot, flip}`
+  (object form, backwards-compat with bare integer). Auto-compacts to
+  bare int when canonical orientation (rot=0+flip=0). `tile.opaque`
+  flag consumed from atlas-baker v0.2.0 alpha-analysis.
+- **v0.5.2** — public vertex-grid write APIs:
+  - `set_vertex(layer_name, vx, vy, painted, map_id?)` — any-corner
+    rule fills up to 4 cells; lazy-allocates grid on first paint
+  - `get_vertex(layer_name, vx, vy, map_id?) -> bool`
+- **v0.5.3** — bugfix: `load_textures` now refreshes the
+  `atlas_by_alias` dict after replacing `m.atlases[i]`, fixing the
+  v3 vertex/material render path which was resolving through the
+  pre-load stub (no texture handle → MISSING_ASSET_COLOR fallback).
+- **v0.5.4** — public atlas accessors for palette consumers:
+  - `atlas_diffuse_handle(atlas_idx, map_id?)` — raylib texture handle
+  - `atlas_tile_size_px(atlas_idx, map_id?)` — int, usually 64
+  - `atlas_tile_uv(atlas_idx, slot, map_id?)` — `{x, y, w, h}` in
+    atlas pixel coords, or `nil`. Resolves slot via the same
+    `slot_NN_` name regex used internally by the renderer.
+
+### Original v0.2.0 entries
+
+
 ### `maps.load(path)`
 **Syntax:** `maps.load(path: string) -> string`