fix(MDS036): address Copilot review feedback

Return all keys from DefaultSettings so re-applying defaults (as the
fixture runner cleanup does) fully clears PerLevel and PerHeading, not
just Max. Add a defensive headingLine fallback for headings with no
line segments, matching the existing pattern in emptysectionbody.

Author: claude

internal/rules/sectionsizelimits/rule.go

@@ -136,9 +136,15 @@ func (r *Rule) ApplySettings(settings map[string]any) error {
 	return nil
 }
 
-// DefaultSettings implements rule.Configurable.
+// DefaultSettings implements rule.Configurable. All keys are returned so
+// re-applying defaults (e.g., test cleanup) fully clears PerLevel and
+// PerHeading, not just Max.
 func (r *Rule) DefaultSettings() map[string]any {
-	return map[string]any{"max": 0}
+	return map[string]any{
+		"max":         0,
+		"per-level":   map[string]any{},
+		"per-heading": []any{},
+	}
 }
 
 func (r *Rule) resolveMax(h heading) int {
@@ -187,7 +193,15 @@ func collectHeadings(f *lint.File) []heading {
 }
 
 func headingLine(h *ast.Heading, f *lint.File) int {
-	return f.LineOfOffset(h.Lines().At(0).Start)
+	if lines := h.Lines(); lines.Len() > 0 {
+		return f.LineOfOffset(lines.At(0).Start)
+	}
+	for c := h.FirstChild(); c != nil; c = c.NextSibling() {
+		if t, ok := c.(*ast.Text); ok {
+			return f.LineOfOffset(t.Segment.Start)
+		}
+	}
+	return 1
 }
 
 func parsePerLevel(v any) (map[int]int, error) {

internal/rules/sectionsizelimits/rule_test.go

@@ -6,6 +6,8 @@ import (
 	"testing"
 
 	"github.com/jeduden/mdsmith/internal/lint"
+	"github.com/yuin/goldmark/ast"
+	gtext "github.com/yuin/goldmark/text"
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -171,6 +173,42 @@ func TestDefaultSettings(t *testing.T) {
 	r := &Rule{}
 	ds := r.DefaultSettings()
 	assert.Equal(t, 0, ds["max"])
+	assert.Equal(t, map[string]any{}, ds["per-level"])
+	assert.Equal(t, []any{}, ds["per-heading"])
+}
+
+func TestHeadingLine_FallbackToTextChild(t *testing.T) {
+	src := []byte("# Hi\n")
+	f, err := lint.NewFile("t.md", src)
+	require.NoError(t, err)
+
+	// Build a heading with no Lines() but with a Text child, to exercise
+	// the defensive fallback.
+	h := ast.NewHeading(1)
+	text := ast.NewTextSegment(gtext.NewSegment(2, 4))
+	h.AppendChild(h, text)
+	assert.Equal(t, 1, headingLine(h, f))
+}
+
+func TestHeadingLine_NoLinesNoChildren(t *testing.T) {
+	f, err := lint.NewFile("t.md", []byte(""))
+	require.NoError(t, err)
+	h := ast.NewHeading(1)
+	assert.Equal(t, 1, headingLine(h, f))
+}
+
+func TestApplyDefaultSettings_ClearsPerLevelAndPerHeading(t *testing.T) {
+	r := &Rule{
+		Max:      10,
+		PerLevel: map[int]int{2: 3},
+		PerHeading: []HeadingPattern{
+			{Pattern: "x", Regex: regexp.MustCompile("x"), Max: 1},
+		},
+	}
+	require.NoError(t, r.ApplySettings(r.DefaultSettings()))
+	assert.Equal(t, 0, r.Max)
+	assert.Empty(t, r.PerLevel)
+	assert.Empty(t, r.PerHeading)
 }
 
 func TestID(t *testing.T) {