diff --git a/init.lua b/init.lua
index 0edec00..fcfb958 100644
--- a/init.lua
+++ b/init.lua
@@ -294,36 +294,46 @@ local function cell_has_material(vertices, cells_material, w, h, x, y)
     return false
 end
 
--- Returns the blob-gated 8-bit neighbour bitmask for cell (x, y) given
--- the layer's vertex grid + map size. Bit layout (clockwise from N):
---   0=N, 1=NE, 2=E, 3=SE, 4=S, 5=SW, 6=W, 7=NW.
+-- Returns the blob-gated 8-bit neighbour bitmask for cell (x, y).
+-- Bit layout (clockwise from N, LSB-first): N, NE, E, SE, S, SW, W, NW.
 --
--- 0.5.6: bits derive from the render-cell's own 4 corner map-tiles
--- (= the 4 surrounding vertices in dual-grid terms), not from the
--- material status of the 8 neighbour cells. A cardinal bit is set iff
--- at least one of the 2 vertices on that edge is painted; a diagonal
--- bit is set iff the corner vertex in that direction is painted.
--- Pre-0.5.6 used cell-neighbour-material, which made two cells with a
--- shared unpainted edge see each other as material whenever any other
--- corner of either was painted — producing connected blobs across
--- visually-empty map-tile gaps. See plan
--- 2026-05-29-painting-model-rethink for the discovery.
+-- 0.5.7: per-cell-origin branch. Cells whose material origin is
+-- cells_material[x, y] use the classical 47-blob 8-neighbour rule on
+-- effective material (vertex-derived OR cell-derived). Vertex-only
+-- cells continue to use the FIX-A 4-own-corner rule (v0.5.6 dual-grid
+-- semantics, 5 reachable atlas slots).
+--
+-- Pre-condition: cell_has_material(vertices, cells_material, w, h, x, y)
+-- returned true for this cell.
 local function compute_cell_bitmask_v3(vertices, cells_material, w, h, x, y)
-    local vw = w + 1
-    local vh = h + 1
-    local TL = vertex_at(vertices, vw, vh, x,     y    ) ~= 0
-    local TR = vertex_at(vertices, vw, vh, x + 1, y    ) ~= 0
-    local BL = vertex_at(vertices, vw, vh, x,     y + 1) ~= 0
-    local BR = vertex_at(vertices, vw, vh, x + 1, y + 1) ~= 0
     local b = 0
-    if TL or TR then b = b | 0x01 end  -- N edge: TL or TR painted
-    if TR       then b = b | 0x02 end  -- NE corner: TR painted
-    if TR or BR then b = b | 0x04 end  -- E edge:  TR or BR painted
-    if BR       then b = b | 0x08 end  -- SE corner: BR painted
-    if BL or BR then b = b | 0x10 end  -- S edge:  BL or BR painted
-    if BL       then b = b | 0x20 end  -- SW corner: BL painted
-    if TL or BL then b = b | 0x40 end  -- W edge:  TL or BL painted
-    if TL       then b = b | 0x80 end  -- NW corner: TL painted
+    if cells_material_at(cells_material, w, h, x, y) ~= 0 then
+        -- 47-blob branch: 8 neighbour effective-material bits.
+        if cell_has_material(vertices, cells_material, w, h, x,     y - 1) then b = b | 0x01 end
+        if cell_has_material(vertices, cells_material, w, h, x + 1, y - 1) then b = b | 0x02 end
+        if cell_has_material(vertices, cells_material, w, h, x + 1, y    ) then b = b | 0x04 end
+        if cell_has_material(vertices, cells_material, w, h, x + 1, y + 1) then b = b | 0x08 end
+        if cell_has_material(vertices, cells_material, w, h, x,     y + 1) then b = b | 0x10 end
+        if cell_has_material(vertices, cells_material, w, h, x - 1, y + 1) then b = b | 0x20 end
+        if cell_has_material(vertices, cells_material, w, h, x - 1, y    ) then b = b | 0x40 end
+        if cell_has_material(vertices, cells_material, w, h, x - 1, y - 1) then b = b | 0x80 end
+    else
+        -- FIX-A 4-corner-vertex branch (v0.5.6 dual-grid, unchanged).
+        local vw = w + 1
+        local vh = h + 1
+        local TL = vertex_at(vertices, vw, vh, x,     y    ) ~= 0
+        local TR = vertex_at(vertices, vw, vh, x + 1, y    ) ~= 0
+        local BL = vertex_at(vertices, vw, vh, x,     y + 1) ~= 0
+        local BR = vertex_at(vertices, vw, vh, x + 1, y + 1) ~= 0
+        if TL or TR then b = b | 0x01 end  -- N
+        if TR       then b = b | 0x02 end  -- NE
+        if TR or BR then b = b | 0x04 end  -- E
+        if BR       then b = b | 0x08 end  -- SE
+        if BL or BR then b = b | 0x10 end  -- S
+        if BL       then b = b | 0x20 end  -- SW
+        if TL or BL then b = b | 0x40 end  -- W
+        if TL       then b = b | 0x80 end  -- NW
+    end
     return apply_blob_gating(b)
 end