2 files changed, 81 insertions, 0 deletions
diff --git a/internal/world/hardening_room_id_mismatch_test.go b/internal/world/hardening_room_id_mismatch_test.go
new file mode 100644
index 0000000..1ac1711
--- /dev/null
+++ b/internal/world/hardening_room_id_mismatch_test.go
@@ -0,0 +1,73 @@
+package world
+
+import (
+	"bytes"
+	"log"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+// Regression: a room file whose declared id: disagrees with its numeric
+// filename was silently loaded under the filename with no diagnostic.
+// World.LoadRoom must warn, because room identity comes from the filename.
+
+func writeRoomFile(t *testing.T, dir, name, body string) {
+	t.Helper()
+	path := filepath.Join(dir, "rooms", name)
+	if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(path, []byte(body), 0o644); err != nil {
+		t.Fatal(err)
+	}
+}
+
+func captureRoomLog(t *testing.T, fn func()) string {
+	t.Helper()
+	var buf bytes.Buffer
+	old := log.Writer()
+	log.SetOutput(&buf)
+	defer log.SetOutput(old)
+	fn()
+	return buf.String()
+}
+
+func TestWorldWarnsOnDeclaredRoomIDMismatch(t *testing.T) {
+	dir := t.TempDir()
+	writeRoomFile(t, dir, "1.yaml", "id: 2\nname: Wrong Id\n")
+	w := New(dir)
+
+	out := captureRoomLog(t, func() {
+		room, err := w.LoadRoom(1)
+		if err != nil {
+			t.Fatalf("load room: %v", err)
+		}
+		if room.ID != 1 {
+			t.Fatalf("filename must win: room.ID = %d, want 1", room.ID)
+		}
+	})
+	if !strings.Contains(out, "declares id") {
+		t.Fatalf("expected a room id-mismatch warning, got log %q", out)
+	}
+}
+
+func TestWorldDoesNotWarnWhenRoomIDMatchesOrAbsent(t *testing.T) {
+	dir := t.TempDir()
+	writeRoomFile(t, dir, "1.yaml", "id: 1\nname: Match\n")
+	writeRoomFile(t, dir, "2.yaml", "name: Absent\n")
+	w := New(dir)
+
+	out := captureRoomLog(t, func() {
+		if _, err := w.LoadRoom(1); err != nil {
+			t.Fatal(err)
+		}
+		if _, err := w.LoadRoom(2); err != nil {
+			t.Fatal(err)
+		}
+	})
+	if strings.Contains(out, "declares id") {
+		t.Fatalf("unexpected room id-mismatch warning: %q", out)
+	}
+}
diff --git a/internal/world/world.go b/internal/world/world.go
index c5d0841..6a0313d 100644
--- a/internal/world/world.go
+++ b/internal/world/world.go
@@ -2,6 +2,7 @@ package world
 
 import (
 	"fmt"
+	"log"
 	"os"
 	"path/filepath"
 	"strconv"
@@ -52,6 +53,13 @@ func (w *World) LoadRoom(id int) (*Room, error) {
 	if err := yaml.Unmarshal(data, &room); err != nil {
 		return nil, fmt.Errorf("parse room %d: %w", id, err)
 	}
+	// Room ID comes from the filename (room.ID = id below); a mismatched
+	// declared id: is silently ignored, so surface it rather than leave the
+	// author believing their written id is in use.
+	if room.ID != 0 && room.ID != id {
+		log.Printf("room %d: file %s declares id %d but is loaded as room %d; the filename is authoritative and the declared id is ignored",
+			id, path, room.ID, id)
+	}
 	room.ID = id
 	if room.Exits == nil {
 		room.Exits = make(map[ExitDir]ExitDef)