diff --git a/init.lua b/init.lua
index d24a44d..abe1ee8 100644
--- a/init.lua
+++ b/init.lua
@@ -388,6 +388,95 @@ function M.run_tests(ctx)
     engine.test.assert(not ok_lay,
         "maps_t1: set_cell_material rejects unknown layer")
 
+    -- =====================================================================
+    -- maps_t2-t7: Cell-Tile slot-resolution proofs
+    -- =====================================================================
+    -- write_test is 4x4. Use v2_size for w/h reference (already declared earlier).
+
+    -- maps_t2: cell_material_slot returns a non-nil record for a
+    -- cells_material cell.
+    -- Clear the surface layer's cells_material first.
+    for cy = 0, v2_size.h - 1 do
+        for cx = 0, v2_size.w - 1 do
+            maps.set_cell_material("surface", cx, cy, false)
+        end
+    end
+    maps.set_cell_material("surface", 1, 1, true)
+    local rec = maps.cell_material_slot("surface", 1, 1)
+    engine.test.assert(rec ~= nil,
+        "maps_t2: cell_material_slot returns non-nil for cell-tile material")
+
+    -- maps_t3: isolated slot reachable for the first time.
+    -- Clear cells_material AND vertices, place an isolated paint at (2, 2).
+    for cy = 0, v2_size.h - 1 do
+        for cx = 0, v2_size.w - 1 do
+            maps.set_cell_material("surface", cx, cy, false)
+            maps.set_vertex("surface", cx, cy, false)
+        end
+        maps.set_vertex("surface", v2_size.w, cy, false)
+    end
+    for cx = 0, v2_size.w do maps.set_vertex("surface", cx, v2_size.h, false) end
+    maps.set_cell_material("surface", 2, 2, true)
+    local r3 = maps.cell_material_slot("surface", 2, 2)
+    engine.test.equals(r3.slot, 0, "maps_t3: slot 0 isolated reachable for first time")
+    engine.test.equals(r3.rot,  0, "maps_t3: isolated rot=0")
+
+    -- maps_t4: two adjacent cells → two end-caps facing each other.
+    maps.set_cell_material("surface", 1, 2, true)
+    maps.set_cell_material("surface", 2, 2, true)
+    local r4a = maps.cell_material_slot("surface", 1, 2)
+    local r4b = maps.cell_material_slot("surface", 2, 2)
+    engine.test.equals(r4a.slot, 1, "maps_t4: left cell is end (slot 1)")
+    engine.test.equals(r4a.rot,  1, "maps_t4: left end points east (rot 1)")
+    engine.test.equals(r4b.slot, 1, "maps_t4: right cell is end (slot 1)")
+    engine.test.equals(r4b.rot,  3, "maps_t4: right end points west (rot 3)")
+
+    -- maps_t5: 3-cell line → middle is straight.
+    maps.set_cell_material("surface", 0, 2, true)
+    -- already painted (1,2) and (2,2) from t4
+    local r5 = maps.cell_material_slot("surface", 1, 2)
+    engine.test.equals(r5.slot, 4, "maps_t5: middle of 3-cell line is straight (slot 4)")
+    -- rot may be 1 or 3 (horizontal canonical); accept both
+    engine.test.assert(r5.rot == 1 or r5.rot == 3,
+        "maps_t5: straight is horizontal (rot 1 or 3)")
+
+    -- Reset surface for t6.
+    for cx = 0, v2_size.w - 1 do
+        maps.set_cell_material("surface", cx, 2, false)
+    end
+
+    -- maps_t6: T-junction at (1, 2) with arms W (0, 2), E (2, 2), S (1, 3).
+    -- write_test is 4x4 so (1, 3) is the last row.
+    maps.set_cell_material("surface", 0, 2, true)
+    maps.set_cell_material("surface", 1, 2, true)
+    maps.set_cell_material("surface", 2, 2, true)
+    maps.set_cell_material("surface", 1, 3, true)
+    local r6 = maps.cell_material_slot("surface", 1, 2)
+    engine.test.equals(r6.slot, 5, "maps_t6: T-junction is tee_open (slot 5)")
+
+    -- Reset for t7.
+    for cy = 0, v2_size.h - 1 do
+        for cx = 0, v2_size.w - 1 do
+            maps.set_cell_material("surface", cx, cy, false)
+        end
+    end
+
+    -- maps_t7: 4-cell "+" at (1, 1) with N (1, 0), E (2, 1), S (1, 2), W (0, 1).
+    maps.set_cell_material("surface", 1, 1, true)
+    maps.set_cell_material("surface", 1, 0, true)
+    maps.set_cell_material("surface", 2, 1, true)
+    maps.set_cell_material("surface", 1, 2, true)
+    maps.set_cell_material("surface", 0, 1, true)
+    local r7 = maps.cell_material_slot("surface", 1, 1)
+    engine.test.equals(r7.slot, 8, "maps_t7: cross is cross_open (slot 8) — second previously-unreachable slot reachable")
+
+    -- Reset surface fully so later tests (if any added) start clean.
+    for cy = 0, v2_size.h - 1 do
+        for cx = 0, v2_size.w - 1 do
+            maps.set_cell_material("surface", cx, cy, false)
+        end
+    end
+
     engine.exit(engine.test.failures())
 end
 
diff --git a/maps/write_test.map.json b/maps/write_test.map.json
index d0a047c..dd6ee4a 100644
--- a/maps/write_test.map.json
+++ b/maps/write_test.map.json
@@ -1,10 +1,18 @@
 {
-  "schema_version": 2,
+  "schema_version": 3,
   "id": "write_test",
   "size": { "w": 4, "h": 4 },
   "atlases": ["demo_tilemap"],
   "layers": {
     "surface": {
+      "material": "demo_tilemap",
+      "vertices": [
+        0, 0, 0, 0, 0,
+        0, 0, 0, 0, 0,
+        0, 0, 0, 0, 0,
+        0, 0, 0, 0, 0,
+        0, 0, 0, 0, 0
+      ],
       "tiles": [
         0, 0, 0, 0,
         0, 0, 0, 0,