1 files changed, 112 insertions, 1 deletions

diff --git a/internal/validate/checks.go b/internal/validate/checks.go
index f1d6b5e..b2e5449 100644
--- a/internal/validate/checks.go
+++ b/internal/validate/checks.go
@@ -6,6 +6,7 @@ import (
 	"strings"
 
 	"thehouseoficarus/internal/behavior"
+	"thehouseoficarus/internal/color"
 	"thehouseoficarus/internal/world"
 )
 
@@ -34,6 +35,13 @@ func validateRooms(s Source) []Issue {
 				Message: fmt.Sprintf("Room %d: has no name", id),
 			})
 		}
+		if room.Color != "" && color.Parse(room.Color).Empty() {
+			issues = append(issues, Issue{
+				Level:   "WARN",
+				Type:    "reference",
+				Message: fmt.Sprintf("Room %d: invalid color %q", id, room.Color),
+			})
+		}
 
 		for dir, exit := range room.Exits {
 			switch dir {
@@ -654,7 +662,7 @@ func validateRoomWiring(s Source) []Issue {
 	roomIndex := s.World.RoomIndex()
 
 	sourceSet := make(map[int]bool)
-	for _, src := range s.CheckSources {
+	for _, src := range s.RootRooms {
 		sourceSet[src] = true
 	}
 
@@ -705,6 +713,109 @@ func validateRoomWiring(s Source) []Issue {
 	return issues
 }
 
+// gridDeltas maps the horizontal exits to their grid movement. Up/Down are
+// intentionally excluded: they connect separate horizontal planes rather than
+// moving within one.
+var gridDeltas = map[world.ExitDir][2]int{
+	world.North: {0, -1},
+	world.South: {0, 1},
+	world.East:  {1, 0},
+	world.West:  {-1, 0},
+}
+
+// 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:
+//   - 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
+// exits to nonexistent rooms are skipped (covered by referential checks).
+func validateRoomGrid(s Source) []Issue {
+	var issues []Issue
+	roomIndex := s.World.RoomIndex()
+
+	placed := make(map[int]bool)
+	var seeds []int
+	for _, r := range s.RootRooms {
+		if roomIndex[r] {
+			seeds = append(seeds, r)
+		}
+	}
+
+	for len(seeds) > 0 {
+		origin := seeds[0]
+		seeds = seeds[1:]
+		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
+			}
+			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 := gridDeltas[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)
+			}
+		}
+	}
+
+	return issues
+}
+
 func validateTechs(s Source) []Issue {
 	var issues []Issue
 	seen := make(map[string]bool)