1 files changed, 33 insertions, 0 deletions
diff --git a/internal/validate/checks.go b/internal/validate/checks.go
index ccf996c..974998a 100644
--- a/internal/validate/checks.go
+++ b/internal/validate/checks.go
@@ -1024,6 +1024,39 @@ func validateRoomGrid(s Source) []Issue {
 		}
 	}
 
+	onConf := func(origin int) func(c world.GridConflict) {
+		return 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),
+				})
+			}
+		}
+	}
+
+	for id := range roomIndex {
+		if placed[id] {
+			continue
+		}
+		grid := world.BuildGrid(id, load, include, onConf(id))
+		for rid := range grid.Coord {
+			placed[rid] = true
+		}
+	}
+
 	return issues
 }