fix: address Copilot review on PR #150

- ToInt/ToFloat reject NaN, +/-Inf, and out-of-range floats so
  invalid config surfaces deterministically instead of yielding
  implementation-dependent int values.
- linelength.applyExclude now uses settings.ToStringSlice so rule
  state does not alias the caller's config slice; drops the local
  toStringSlice duplicate.

Author: claude

internal/rules/linelength/rule.go

@@ -115,7 +115,7 @@ func (r *Rule) applyStern(v any) error {
 }
 
 func (r *Rule) applyExclude(v any) error {
-	list, ok := toStringSlice(v)
+	list, ok := settings.ToStringSlice(v)
 	if !ok {
 		return fmt.Errorf("line-length: exclude must be a list of strings, got %T", v)
 	}
@@ -316,26 +316,6 @@ func headingLineNum(h *ast.Heading, f *lint.File) int {
 	return 0
 }
 
-// toStringSlice converts a value to []string. YAML decodes sequences as
-// []any with string elements.
-func toStringSlice(v any) ([]string, bool) {
-	switch s := v.(type) {
-	case []string:
-		return s, true
-	case []any:
-		result := make([]string, 0, len(s))
-		for _, item := range s {
-			str, ok := item.(string)
-			if !ok {
-				return nil, false
-			}
-			result = append(result, str)
-		}
-		return result, true
-	}
-	return nil, false
-}
-
 func isValidExclude(s string) bool {
 	return s == "code-blocks" || s == "tables" || s == "urls"
 }

internal/rules/settings/settings.go

@@ -8,26 +8,37 @@
 // with consistent behavior and a single set of tests.
 package settings
 
+import "math"
+
 // ToInt coerces v to an int when v is int, int64, or float64.
-// Float inputs are truncated toward zero. Other types (string, bool,
-// nil, slices) are rejected.
+// Float inputs are truncated toward zero. NaN, +/-Inf, and float
+// values outside the int range are rejected (ok=false).
 func ToInt(v any) (int, bool) {
 	switch n := v.(type) {
 	case int:
 		return n, true
 	case int64:
 		return int(n), true
 	case float64:
+		if math.IsNaN(n) || math.IsInf(n, 0) {
+			return 0, false
+		}
+		if n < math.MinInt || n > math.MaxInt {
+			return 0, false
+		}
 		return int(n), true
 	}
 	return 0, false
 }
 
 // ToFloat coerces v to a float64 when v is float64, int, or int64.
-// Other types are rejected.
+// NaN and +/-Inf are rejected. Other types are rejected.
 func ToFloat(v any) (float64, bool) {
 	switch n := v.(type) {
 	case float64:
+		if math.IsNaN(n) || math.IsInf(n, 0) {
+			return 0, false
+		}
 		return n, true
 	case int:
 		return float64(n), true

internal/rules/settings/settings_test.go

@@ -1,6 +1,7 @@
 package settings_test
 
 import (
+	"math"
 	"testing"
 
 	"github.com/jeduden/mdsmith/internal/rules/settings"
@@ -21,6 +22,11 @@ func TestToInt(t *testing.T) {
 		{"float64-whole", 5.0, 5, true},
 		{"float64-truncates", 3.9, 3, true},
 		{"float64-negative-truncates", -2.7, -2, true},
+		{"float64-nan-rejected", math.NaN(), 0, false},
+		{"float64-posinf-rejected", math.Inf(1), 0, false},
+		{"float64-neginf-rejected", math.Inf(-1), 0, false},
+		{"float64-overflow-rejected", 1e20, 0, false},
+		{"float64-underflow-rejected", -1e20, 0, false},
 		{"string-rejected", "5", 0, false},
 		{"bool-rejected", true, 0, false},
 		{"nil-rejected", nil, 0, false},
@@ -46,6 +52,9 @@ func TestToFloat(t *testing.T) {
 		{"float64-zero", 0.0, 0.0, true},
 		{"int", 4, 4.0, true},
 		{"int64", int64(9), 9.0, true},
+		{"float64-nan-rejected", math.NaN(), 0, false},
+		{"float64-posinf-rejected", math.Inf(1), 0, false},
+		{"float64-neginf-rejected", math.Inf(-1), 0, false},
 		{"string-rejected", "1.5", 0, false},
 		{"bool-rejected", false, 0, false},
 		{"nil-rejected", nil, 0, false},