Warn when masterfeat expansion silently drops unobtainable feats

classFeatExpansionCanUseFeat excludes ALLCLASSESCANUSE=0 feats from
class feat table masterfeat expansion. When such a feat also has no
MinLevelClass, no class can ever obtain it — a data bug that previously
failed silently (e.g. Spell Focus vanishing from the wizard table).

New validator warns for exactly that case; deliberate exclusions with
an explicit MinLevelClass stay silent.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

internal/topdata/class_feat_accessibility.go

@@ -0,0 +1,98 @@
+package topdata
+
+import (
+	"fmt"
+	"path/filepath"
+	"slices"
+	"strings"
+)
+
+// validateClassFeatMasterfeatAccessibility warns when a class feat table
+// references a masterfeat whose member feats are silently dropped from
+// expansion by classFeatExpansionCanUseFeat. Only the ambiguous case is
+// flagged: ALLCLASSESCANUSE=0 with no MinLevelClass, where the feat cannot
+// be obtained by any class at all. Exclusions with an explicit MinLevelClass
+// are deliberate cross-class restrictions and stay silent.
+func validateClassFeatMasterfeatAccessibility(dataDir string, report *ValidationReport) {
+	datasets, err := discoverNativeDatasets(dataDir)
+	if err != nil {
+		return
+	}
+	keyToID := map[string]int{}
+	var featRowByKey map[string]map[string]any
+	type classFeatTable struct {
+		path     string
+		classKey string
+		rows     []map[string]any
+	}
+	classTables := []classFeatTable{}
+	for _, dataset := range datasets {
+		name := filepath.ToSlash(dataset.Name)
+		isClassFeats := strings.HasPrefix(name, "classes/feats/")
+		if name != "feat" && name != "masterfeats" && name != "classes/core" && !isClassFeats {
+			continue
+		}
+		collected, err := collectNativeDataset(dataset)
+		if err != nil {
+			return
+		}
+		for key, id := range collected.LockData {
+			keyToID[key] = id
+		}
+		switch {
+		case name == "feat":
+			featRowByKey = rowsByKey(collected.Rows)
+		case isClassFeats:
+			classTables = append(classTables, classFeatTable{
+				path:     dataset.BasePath,
+				classKey: "classes:" + name[strings.LastIndex(name, "/")+1:],
+				rows:     collected.Rows,
+			})
+		}
+	}
+	if featRowByKey == nil {
+		return
+	}
+	for _, table := range classTables {
+		for _, row := range table.rows {
+			featRef, ok := row["FeatIndex"].(map[string]any)
+			if !ok {
+				continue
+			}
+			refKey, _ := featRef["id"].(string)
+			if !strings.HasPrefix(refKey, "masterfeats:") {
+				continue
+			}
+			masterfeatKey := resolveCanonicalDatasetKey(refKey, keyToID)
+			if _, ok := keyToID[masterfeatKey]; !ok {
+				continue
+			}
+			featKeys := make([]string, 0, len(featRowByKey))
+			for featKey := range featRowByKey {
+				if strings.HasPrefix(featKey, "feat:") {
+					featKeys = append(featKeys, featKey)
+				}
+			}
+			slices.Sort(featKeys)
+			for _, featKey := range featKeys {
+				featRow := featRowByKey[featKey]
+				if !rowReferencesMasterfeat(featRow, masterfeatKey, keyToID) {
+					continue
+				}
+				if classFeatExpansionCanUseFeat(featRow, table.classKey, keyToID) {
+					continue
+				}
+				if minLevelClass, ok := lookupField(featRow, "MinLevelClass"); ok && !isNullishValue(minLevelClass) {
+					continue
+				}
+				report.Diagnostics = append(report.Diagnostics, Diagnostic{
+					Severity: SeverityWarning,
+					Path:     table.path,
+					Message: fmt.Sprintf(
+						"%s references %s but %s is excluded from expansion (ALLCLASSESCANUSE=0 with no MinLevelClass makes it unobtainable); override ALLCLASSESCANUSE or set MinLevelClass",
+						table.classKey, masterfeatKey, featKey),
+				})
+			}
+		}
+	}
+}