1 files changed, 37 insertions, 65 deletions

diff --git a/internal/validate/checks.go b/internal/validate/checks.go
index a41ad86..d835a53 100644
--- a/internal/validate/checks.go
+++ b/internal/validate/checks.go
@@ -870,20 +870,29 @@ func validateRoomWiring(s Source) []Issue {
 }
 
 
-// validateRoomGrid lays each reachable horizontal plane on a 2D grid starting
-// from the configured root rooms and reports when the exit layout cannot be
-// embedded without conflict:
+// validateRoomGrid embeds the entire reachable world on a single 3D grid
+// starting from the configured root rooms and reports when the exit layout
+// cannot be embedded without conflict:
 //   - overlap: two distinct rooms land on the same grid cell.
 //   - twist:   one room is forced onto two different grid cells.
 //
-// Up/Down exits don't move on the grid; each leads to a new plane that is laid
-// out independently (fresh origin), so one root validates every reachable
-// floor. Exit conditions are ignored (geometry is independent of gating), and
+// All 10 exits (including Up/Down) participate in coordinate assignment:
+// horizontal exits shift (x,y); Up/Down shift z at the same (x,y).
+// Exit conditions are ignored (geometry is independent of gating), and
 // exits to nonexistent rooms are skipped (covered by referential checks).
 func validateRoomGrid(s Source) []Issue {
 	var issues []Issue
 	roomIndex := s.World.RoomIndex()
 
+	load := func(id int) (*world.Room, bool) {
+		r, err := s.World.LoadRoom(id)
+		if err != nil {
+			return nil, false
+		}
+		return r, true
+	}
+	include := func(id int) bool { return roomIndex[id] }
+
 	placed := make(map[int]bool)
 	var seeds []int
 	for _, r := range s.RootRooms {
@@ -892,71 +901,34 @@ func validateRoomGrid(s Source) []Issue {
 		}
 	}
 
-	for len(seeds) > 0 {
-		origin := seeds[0]
-		seeds = seeds[1:]
+	for _, origin := range seeds {
 		if placed[origin] {
 			continue
 		}
 
-		coordOf := map[int][2]int{origin: {0, 0}}
-		roomAt := map[[2]int]int{{0, 0}: origin}
-		placed[origin] = true
-		queue := []int{origin}
-
-		for len(queue) > 0 {
-			rid := queue[0]
-			queue = queue[1:]
-			room, err := s.World.LoadRoom(rid)
-			if err != nil {
-				continue
+		grid := world.BuildGrid(origin, load, include, func(c world.GridConflict) {
+			switch c.Kind {
+			case "twist":
+				issues = append(issues, Issue{
+					Level: "ERROR",
+					Type:  "integrity",
+					Message: fmt.Sprintf(
+						"Grid twist: room %d (via %d %s) maps to (%d,%d,%d) but was already placed at (%d,%d,%d) [origin %d]",
+						c.Target, c.From, c.Dir, c.Want[0], c.Want[1], c.Want[2], c.Existing[0], c.Existing[1], c.Existing[2], origin),
+				})
+			case "overlap":
+				issues = append(issues, Issue{
+					Level: "ERROR",
+					Type:  "integrity",
+					Message: fmt.Sprintf(
+						"Grid overlap: room %d (via %d %s) wants (%d,%d,%d), already used by room %d [origin %d]",
+						c.Target, c.From, c.Dir, c.Want[0], c.Want[1], c.Want[2], c.Occupier, origin),
+				})
 			}
-			c := coordOf[rid]
-			for _, dir := range world.ExitOrder {
-				exit, ok := room.Exits[dir]
-				if !ok || exit.Room <= 0 || !roomIndex[exit.Room] {
-					continue
-				}
-				target := exit.Room
-
-				if dir == world.Up || dir == world.Down {
-					if !placed[target] {
-						seeds = append(seeds, target)
-					}
-					continue
-				}
-
-				d := world.DirectionDeltas[dir]
-				want := [2]int{c[0] + d[0], c[1] + d[1]}
-
-				if existing, ok := coordOf[target]; ok {
-					if existing != want {
-						issues = append(issues, Issue{
-							Level: "ERROR",
-							Type:  "integrity",
-							Message: fmt.Sprintf(
-								"Grid twist: room %d (via %d %s) maps to grid (%d,%d) but was already placed at (%d,%d) [plane origin %d]",
-								target, rid, dir, want[0], want[1], existing[0], existing[1], origin),
-						})
-					}
-					continue
-				}
-				if occupier, ok := roomAt[want]; ok && occupier != target {
-					issues = append(issues, Issue{
-						Level: "ERROR",
-						Type:  "integrity",
-						Message: fmt.Sprintf(
-							"Grid overlap: room %d (via %d %s) wants grid (%d,%d), already used by room %d [plane origin %d]",
-							target, rid, dir, want[0], want[1], occupier, origin),
-					})
-					continue
-				}
+		})
 
-				coordOf[target] = want
-				roomAt[want] = target
-				placed[target] = true
-				queue = append(queue, target)
-			}
+		for rid := range grid.Coord {
+			placed[rid] = true
 		}
 	}