diff --git a/src/gen/connect.lua b/src/gen/connect.lua
new file mode 100644
index 0000000..6720b9f
--- /dev/null
+++ b/src/gen/connect.lua
@@ -0,0 +1,79 @@
+-- Guarantees every walkable cell is reachable. Labels connected components with
+-- a deterministic flood fill, then tunnels each secondary component into the
+-- largest one along the shortest Manhattan link. Returns the cells of the final
+-- reachable region in index order.
+
+local Carve = require("gen.carve")
+
+local Connect = {}
+
+local NEIGHBOURS = { { 1, 0 }, { -1, 0 }, { 0, 1 }, { 0, -1 } }
+
+local function label(map)
+  local component = {}
+  local components = {}
+  for y = 1, map.height do
+    for x = 1, map.width do
+      local idx = map:index(x, y)
+      if map:isWalkable(x, y) and not component[idx] then
+        local cells = {}
+        local stack = { { x, y } }
+        component[idx] = #components + 1
+        while #stack > 0 do
+          local cell = stack[#stack]
+          stack[#stack] = nil
+          cells[#cells + 1] = { x = cell[1], y = cell[2] }
+          for _, step in ipairs(NEIGHBOURS) do
+            local nx, ny = cell[1] + step[1], cell[2] + step[2]
+            if map:inBounds(nx, ny) and map:isWalkable(nx, ny) then
+              local nIdx = map:index(nx, ny)
+              if not component[nIdx] then
+                component[nIdx] = #components + 1
+                stack[#stack + 1] = { nx, ny }
+              end
+            end
+          end
+        end
+        table.sort(cells, function(a, b)
+          return map:index(a.x, a.y) < map:index(b.x, b.y)
+        end)
+        components[#components + 1] = cells
+      end
+    end
+  end
+  return components
+end
+
+local function nearestPair(from, to, map)
+  local best, bx, by, tx, ty = math.huge
+  for _, a in ipairs(from) do
+    for _, b in ipairs(to) do
+      local dist = math.abs(a.x - b.x) + math.abs(a.y - b.y)
+      if dist < best then
+        best, bx, by, tx, ty = dist, a.x, a.y, b.x, b.y
+      end
+    end
+  end
+  return bx, by, tx, ty
+end
+
+function Connect.ensure(map, rng)
+  local components = label(map)
+  if #components == 0 then return {} end
+  table.sort(components, function(a, b)
+    if #a ~= #b then return #a > #b end
+    return map:index(a[1].x, a[1].y) < map:index(b[1].x, b[1].y)
+  end)
+  local main = components[1]
+  for i = 2, #components do
+    local ax, ay, bx, by = nearestPair(components[i], main, map)
+    Carve.corridor(map, ax, ay, bx, by, rng)
+  end
+  local reachable = label(map)[1] or main
+  table.sort(reachable, function(a, b)
+    return map:index(a.x, a.y) < map:index(b.x, b.y)
+  end)
+  return reachable
+end
+
+return Connect
diff --git a/src/gen/prefab.lua b/src/gen/prefab.lua
new file mode 100644
index 0000000..4130d53
--- /dev/null
+++ b/src/gen/prefab.lua
@@ -0,0 +1,87 @@
+-- Hand-authored vaults stamped onto a generated level. Each vault is an ASCII
+-- template; markers flag where the dungeon layer should later drop treasure or
+-- guardians. Stamping is deterministic given a fixed anchor.
+
+local Tiles = require("tiles")
+
+local Prefab = {}
+
+Prefab.vaults = {
+  {
+    name = "treasureCell",
+    rows = {
+      "#########",
+      "#.......#",
+      "#.#####.#",
+      "#.#*M*#.#",
+      "#.#*L*#+#",
+      "#.#####.#",
+      "#.......#",
+      "#########",
+    },
+  },
+  {
+    name = "guardPost",
+    rows = {
+      "#######",
+      "#M...M#",
+      "#..*..#",
+      "#M...M#",
+      "#######",
+    },
+  },
+  {
+    name = "flooded",
+    rows = {
+      "#########",
+      "#~~...~~#",
+      "#~..*..~#",
+      "#..MLM..#",
+      "#~..*..~#",
+      "#~~...~~#",
+      "#########",
+    },
+  },
+}
+
+local glyphFor = {
+  ["#"] = Tiles.WALL,
+  ["."] = Tiles.FLOOR,
+  ["+"] = Tiles.DOOR_CLOSED,
+  ["~"] = Tiles.WATER,
+  ["*"] = Tiles.FLOOR,
+  ["M"] = Tiles.FLOOR,
+  ["L"] = Tiles.FLOOR,
+}
+
+function Prefab.size(vault)
+  return #vault.rows[1], #vault.rows
+end
+
+-- Returns true when a vault fits entirely inside the map interior with a wall
+-- gap to the border, false otherwise. No cell content is inspected here; the
+-- caller decides overlap policy.
+function Prefab.fits(map, vault, ox, oy)
+  local w, h = Prefab.size(vault)
+  return ox >= 2 and oy >= 2 and ox + w - 1 <= map.width - 1 and oy + h - 1 <= map.height - 1
+end
+
+-- Stamps a vault at (ox, oy) and returns lists of treasure and monster anchors
+-- in map coordinates so the dungeon layer can populate them.
+function Prefab.stamp(map, vault, ox, oy)
+  local treasure, monsters, loot = {}, {}, {}
+  for row = 1, #vault.rows do
+    local line = vault.rows[row]
+    for col = 1, #line do
+      local mark = line:sub(col, col)
+      local x, y = ox + col - 1, oy + row - 1
+      map:set(x, y, glyphFor[mark] or Tiles.FLOOR)
+      if mark == "*" then treasure[#treasure + 1] = { x = x, y = y } end
+      if mark == "M" then monsters[#monsters + 1] = { x = x, y = y } end
+      if mark == "L" then loot[#loot + 1] = { x = x, y = y } end
+    end
+  end
+  return { name = vault.name, treasure = treasure, monsters = monsters, loot = loot }
+end
+
+return Prefab