diff --git a/README.md b/README.md
index b3eb61a..90ca027 100644
--- a/README.md
+++ b/README.md
@@ -131,3 +131,25 @@ future engine + lib slice.
 All previous hotkeys (Tab, S, E, R, H, 0, D, G, I, Esc) continue to
 work; their bindings are documented in the items where applicable
 and in the in-editor Cheatsheet modal.
+
+## Cell-Tile Mode (v0.3.1)
+
+Third painting mechanic alongside Auto-Tile and Direct. LMB paints a
+per-cell material flag at the cursor cell; RMB clears it. The
+renderer uses the classical 47-blob 8-neighbour bitmask for
+cell-tile cells, unlocking the 9 atlas slots that Auto-Tile's
+dual-grid 4-corner rule structurally cannot reach (isolated, end,
+corner_open, straight, tee_open, tee_half, cross_open, cross_q1,
+cross_q2adj).
+
+Auto-Tile (vertex-paint, 5 reachable slots, dual-grid look) and
+Direct (manual override placement, all 14 slots via explicit pick)
+are unchanged. Tab cycles through all three modes.
+
+For clean visuals, use a single painting mode per layer. Mixing
+Vertex-Tile and Cell-Tile material in the same layer is allowed but
+produces an asymmetric seam at the boundary because vertex-tile
+cells are structurally blind to their cell-tile neighbours.
+
+See `sporel-meta/docs/superpowers/specs/2026-06-01-map-editor-cell-tile-mode-design.md`
+for the full design rationale and the Boris-taxonomy background.
diff --git a/init.lua b/init.lua
index 7a537fd..219da21 100644
--- a/init.lua
+++ b/init.lua
@@ -1,4 +1,4 @@
--- sporel-module-map-editor v0.3.0
+-- sporel-module-map-editor v0.3.1
 -- Interactive map editor — Rev 4 UX architecture (see design paper
 -- 2026-05-28-autotile-blob-styles-design.md §11 + plan stub
 -- 2026-05-28-map-editor-blob-v2.md). 0.2.0b adds the bottom palette
@@ -613,7 +613,7 @@ local ui = (function()
 
     -- Cheatsheet content (rendered into the modal).
     local CHEATSHEET = {
-        { key="Tab",   action="Toggle mode (Auto-Tile / Direct)" },
+        { key="Tab",   action="Cycle mode (Auto-Tile / Cell-Tile / Direct)" },
         { key="I",     action="Show / hide this cheatsheet" },
         { key="S",     action="Save current map to work.map.json" },
         { key="E",     action="Erase tile at mouse cell" },
@@ -1513,7 +1513,7 @@ input.bind("reset_transform",   { "0" })     -- 0.2.0c
 input.bind("toggle_debug_overlay", { "d" })  -- 0.2.0c.3
 input.bind("toggle_world_overlay", { "g" })  -- 0.2.0c.4
 
-engine.print("map-editor v0.3.0: ready. Tab=cycle mode, I=help, G=grid, D=debug, S=save, E=erase, R=rotate, H=flip, 0=reset, ESC=quit / close")
+engine.print("map-editor v0.3.1: ready. Tab=cycle mode (Auto/Cell/Direct), I=help, G=grid, D=debug, S=save, E=erase, R=rotate, H=flip, 0=reset, ESC=quit / close")
 
 -- =====================================================================
 -- 0.3.0: self-tests (Spec §7.1). Run once on the first CI frame.
diff --git a/manifest.module b/manifest.module
index a723fc6..c5a1c88 100644
--- a/manifest.module
+++ b/manifest.module
@@ -1,6 +1,6 @@
 {
     "id": "map-editor",
-    "version": "0.3.0",
+    "version": "0.3.1",
     "kind": "module",
     "api": "^0.1",
     "ci_frames": 30,