4 files changed, 211 insertions, 0 deletions
diff --git a/internal/validate/checks.go b/internal/validate/checks.go
index 9d09eef..5eb4288 100644
--- a/internal/validate/checks.go
+++ b/internal/validate/checks.go
@@ -736,6 +736,7 @@ func validateDropTables(s Source) []Issue {
 	var issues []Issue
 	dropIDs := dropTableIDSet(s.DataDir)
 	itemIDs := s.Items.IDSet()
+	issues = append(issues, validateDropTableCycles(s, dropIDs)...)
 
 	for id := range dropIDs {
 		dt, err := behavior.LoadDropTable(s.DataDir, id)
@@ -838,6 +839,72 @@ func validateDropTables(s Source) []Issue {
 	return issues
 }
 
+// validateDropTableCycles reports every table that participates in a
+// reference cycle. ResolveDrop recurses at runtime, so a self- or
+// mutual-reference would otherwise overflow the goroutine stack and kill the
+// process; a cycle is therefore a hard startup error.
+func validateDropTableCycles(s Source, dropIDs map[string]bool) []Issue {
+	edges := make(map[string][]string, len(dropIDs))
+	for id := range dropIDs {
+		dt, err := behavior.LoadDropTable(s.DataDir, id)
+		if err != nil {
+			continue // reported by the main pass
+		}
+		for _, d := range dt.Drops {
+			if d.Table != "" && dropIDs[d.Table] {
+				edges[id] = append(edges[id], d.Table)
+			}
+		}
+	}
+	const (
+		white = 0
+		gray  = 1
+		black = 2
+	)
+	color := make(map[string]int, len(dropIDs))
+	reported := make(map[string]bool)
+	var stack []string
+	var issues []Issue
+	var visit func(id string)
+	visit = func(id string) {
+		color[id] = gray
+		stack = append(stack, id)
+		for _, next := range edges[id] {
+			switch color[next] {
+			case gray:
+				start := 0
+				for i, m := range stack {
+					if m == next {
+						start = i
+						break
+					}
+				}
+				for _, m := range stack[start:] {
+					if reported[m] {
+						continue
+					}
+					reported[m] = true
+					issues = append(issues, Issue{
+						Level:   "ERROR",
+						Type:    "integrity",
+						Message: fmt.Sprintf("Drop table %q participates in a reference cycle; drop-table recursion would overflow the stack", m),
+					})
+				}
+			case white:
+				visit(next)
+			}
+		}
+		stack = stack[:len(stack)-1]
+		color[id] = black
+	}
+	for id := range dropIDs {
+		if color[id] == white {
+			visit(id)
+		}
+	}
+	return issues
+}
+
 func validateCourses(s Source) []Issue {
 	var issues []Issue
 	roomIndex := s.World.RoomIndex()
diff --git a/internal/validate/regression_test.go b/internal/validate/regression_test.go
new file mode 100644
index 0000000..53475bd
--- /dev/null
+++ b/internal/validate/regression_test.go
@@ -0,0 +1,45 @@
+package validate
+
+import (
+	"path/filepath"
+	"testing"
+
+	"thehouseoficarus/internal/behavior"
+)
+
+// TestDropTableCycleIsAnError: a self/mutual drop-table reference must be a
+// startup ERROR, because ResolveDrop recurses and would otherwise overflow the
+// goroutine stack at runtime.
+func TestDropTableCycleIsAnError(t *testing.T) {
+	dir := t.TempDir()
+	writeFile(t, filepath.Join(dir, "drops", "a.yaml"), "id: a\ndrops:\n  - table: b\n    weight: 1\n")
+	writeFile(t, filepath.Join(dir, "drops", "b.yaml"), "id: b\ndrops:\n  - table: a\n    weight: 1\n")
+	behavior.ClearDropIndex()
+	defer behavior.ClearDropIndex()
+
+	issues := validateDropTableCycles(Source{DataDir: dir}, dropTableIDSet(dir))
+	if len(issues) == 0 {
+		t.Fatal("expected a cycle error for a <-> b")
+	}
+	for _, issue := range issues {
+		if issue.Level != "ERROR" {
+			t.Fatalf("cycle issue must be ERROR: %+v", issue)
+		}
+	}
+}
+
+// TestNonNumericRoomFilenameIsAnError: the room index only accepts numeric
+// stems, so a backup file must be flagged instead of silently ignored.
+func TestNonNumericRoomFilenameIsAnError(t *testing.T) {
+	dir := t.TempDir()
+	writeFile(t, filepath.Join(dir, "rooms", "1001.yaml"), "id: 1001\nname: real\n")
+	writeFile(t, filepath.Join(dir, "rooms", "1001_copy.yaml"), "id: 1001\nname: copy\n")
+
+	issues := validateRoomFilenames(dir)
+	if len(issues) != 1 {
+		t.Fatalf("expected exactly one filename issue, got %+v", issues)
+	}
+	if issues[0].Level != "ERROR" {
+		t.Fatalf("expected ERROR, got %+v", issues[0])
+	}
+}
diff --git a/internal/validate/shipped_data_test.go b/internal/validate/shipped_data_test.go
new file mode 100644
index 0000000..9c5bef1
--- /dev/null
+++ b/internal/validate/shipped_data_test.go
@@ -0,0 +1,20 @@
+package validate
+
+import (
+	"path/filepath"
+	"testing"
+)
+
+// TestShippedDataHasNoUnknownFields guards the authored content tree against
+// misspelled or stale YAML keys: every data file is decoded with
+// KnownFields(true), so an unread key (like the old exit-level
+// set_player_flags or the legacy triggers key) fails CI instead of being
+// silently discarded at load time.
+func TestShippedDataHasNoUnknownFields(t *testing.T) {
+	dataDir := filepath.Join("..", "..", "data")
+	for _, issue := range validateKnownFields(dataDir) {
+		if issue.Level == "ERROR" {
+			t.Errorf("%s", issue.Message)
+		}
+	}
+}
diff --git a/internal/validate/validate.go b/internal/validate/validate.go
index 735c9ef..8ca4555 100644
--- a/internal/validate/validate.go
+++ b/internal/validate/validate.go
@@ -6,13 +6,18 @@
 package validate
 
 import (
+	"bytes"
 	"fmt"
 	"os"
 	"path/filepath"
 	"sort"
+	"strconv"
 	"strings"
 
+	"gopkg.in/yaml.v3"
+
 	"thehouseoficarus/internal/behavior"
+	"thehouseoficarus/internal/cardart"
 	"thehouseoficarus/internal/item"
 	"thehouseoficarus/internal/object"
 	"thehouseoficarus/internal/world"
@@ -67,6 +72,9 @@ func Run(s Source) []Issue {
 		issues = append(issues, validateIDs(s.DataDir, dir.sub, dir.label)...)
 	}
 
+	issues = append(issues, validateKnownFields(s.DataDir)...)
+	issues = append(issues, validateRoomFilenames(s.DataDir)...)
+
 	issues = append(issues, validateRooms(s)...)
 	issues = append(issues, validateMobs(s)...)
 	issues = append(issues, validateHazards(s)...)
@@ -84,6 +92,77 @@ func Run(s Source) []Issue {
 	return issues
 }
 
+// validateRoomFilenames flags room files whose name is not a plain integer:
+// the room index only accepts numeric stems, so a file like
+// "1001_copy.yaml" would otherwise be silently ignored (and, before the
+// strconv fix, could shadow the real room 1001).
+func validateRoomFilenames(dataDir string) []Issue {
+	dir := filepath.Join(dataDir, "rooms")
+	var issues []Issue
+	_ = behavior.WalkYAMLDir(dir, func(path, id string, data []byte) error {
+		if _, err := strconv.Atoi(id); err != nil {
+			rel := strings.TrimPrefix(path, dataDir+"/")
+			issues = append(issues, Issue{
+				Level:   "ERROR",
+				Type:    "integrity",
+				Message: fmt.Sprintf("room %s: filename is not a numeric room ID and the file is ignored", rel),
+			})
+		}
+		return nil
+	})
+	return issues
+}
+
+// validateKnownFields decodes every authored data file with KnownFields(true)
+// so a misspelled or stale YAML key is a startup ERROR instead of being
+// silently discarded by yaml.Unmarshal. Only package-owned content types are
+// covered (world/object/item/behavior); game-owned definitions are checked by
+// their own loaders.
+func validateKnownFields(dataDir string) []Issue {
+	targets := []struct {
+		subDir string
+		label  string
+		newDef func() any
+	}{
+		{"rooms", "room", func() any { return new(world.Room) }},
+		{"mobs", "mob", func() any { return new(world.MobDef) }},
+		{"objects", "object", func() any { return new(object.ObjectDef) }},
+		{"items", "item", func() any { return new(item.ItemDef) }},
+		{"drops", "drop table", func() any { return new(behavior.DropTableDef) }},
+		{"hazards", "hazard", func() any { return new(world.HazardDef) }},
+	}
+	var issues []Issue
+	for _, t := range targets {
+		dir := filepath.Join(dataDir, t.subDir)
+		_ = behavior.WalkYAMLDir(dir, func(path, id string, data []byte) error {
+			dec := yaml.NewDecoder(bytes.NewReader(data))
+			dec.KnownFields(true)
+			if err := dec.Decode(t.newDef()); err != nil {
+				rel := strings.TrimPrefix(path, dataDir+"/")
+				issues = append(issues, Issue{
+					Level:   "ERROR",
+					Type:    "unknown-field",
+					Message: fmt.Sprintf("%s %s: %v", t.label, rel, err),
+				})
+			}
+			return nil
+		})
+	}
+	// cards.yaml lives at the data root rather than a subdirectory.
+	if data, err := os.ReadFile(filepath.Join(dataDir, "cards.yaml")); err == nil {
+		dec := yaml.NewDecoder(bytes.NewReader(data))
+		dec.KnownFields(true)
+		if err := dec.Decode(new(cardart.Store)); err != nil {
+			issues = append(issues, Issue{
+				Level:   "ERROR",
+				Type:    "unknown-field",
+				Message: fmt.Sprintf("cards.yaml: %v", err),
+			})
+		}
+	}
+	return issues
+}
+
 func validateIDs(dataDir, subDir, label string) []Issue {
 	dir := filepath.Join(dataDir, subDir)
 	dups := behavior.CheckDuplicateIDs(dir)