feat(maps): v0.5.5 — cell_material_slot public getter

Exposes what the v3 vertex/material render path computes internally:
per (layer, x, y), returns {slot, rot, flip} for material cells,
nil for non-material. Override entry wins (normalised via existing
normalize_override_entry); otherwise resolves through
compute_cell_bitmask_v3 + SLOT_LOOKUP.

Primary consumer: debug-overlay tooling (map-editor 0.2.0c.3) that
labels each rendered cell with its blob-14 slot identity for
authoring verification.

init.lua

@@ -1230,6 +1230,32 @@ function M.atlas_tile_size_px(atlas_idx, map_id)
     return atlas and atlas.tile_size_px or nil
 end
 
+-- 0.5.5: public version of what the v3 vertex/material render path
+-- computes internally. Returns {slot, rot, flip} for a material cell
+-- (override entry takes precedence, else vertex-bitmask-derived), or
+-- nil when the cell is non-material / the layer is non-material-bound.
+-- Primary consumer: debug-overlay tooling that wants to label each
+-- rendered cell with its blob-14 slot identity.
+function M.cell_material_slot(layer_name, x, y, map_id)
+    local id = map_id or current_map_id
+    if not id then error("maps.cell_material_slot: no current map") end
+    local m = map_registry[id]
+    if not m.layers or not m.layers[layer_name] then return nil end
+    local layer = m.layers[layer_name]
+    if not layer.material then return nil end
+    if x < 0 or x >= m.size.w or y < 0 or y >= m.size.h then return nil end
+    -- Override wins (sparse force-slot map)
+    local entry = layer.overrides and layer.overrides[x .. ":" .. y]
+    if entry ~= nil then
+        return normalize_override_entry(entry)
+    end
+    -- Vertex-derived bitmask path (only if the layer has a vertex grid)
+    if not layer.vertices then return nil end
+    if not cell_has_material(layer.vertices, m.size.w, m.size.h, x, y) then return nil end
+    local bitmask = compute_cell_bitmask_v3(layer.vertices, m.size.w, m.size.h, x, y)
+    return SLOT_LOOKUP[bitmask]
+end
+
 function M.atlas_tile_uv(atlas_idx, slot, map_id)
     local id = map_id or current_map_id
     if not id then error("maps.atlas_tile_uv: no current map") end

manifest.lib

@@ -1 +1 @@
-{"id":"lib-core.maps","version":"0.5.4","api_min":"0.1"}
+{"id":"lib-core.maps","version":"0.5.5","api_min":"0.1"}