fix: address Copilot review and coverage gaps

- Remove dangling isTable comments from paragraphreadability and
  paragraphstructure (leftover from the private helper deletion)
- Add TestHeadingLine_WalkDescendsIntoNonTextChild to cover the
  ast.Walk body in HeadingLine (reached only via synthetic headings
  with no Lines() set; real goldmark ATX headings always set Lines())
- Add TestHeadingLastLine_NoLines_FallsBackToAstutil to cover the
  astutil.HeadingLine fallback in headingLastLine
- Add TestHeadingText_LinkText, TestExtractText_LinkNode, and
  TestHeadingText_AndExtractText_NoChildren as requested by Copilot;
  these also document behavior for links and empty nodes
- astutil package now has 100% statement coverage

https://claude.ai/code/session_01YbFAKES95Szi7i251Yv1XE

Author: claude

internal/rules/astutil/astutil_test.go

@@ -8,6 +8,7 @@ import (
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 	"github.com/yuin/goldmark/ast"
+	"github.com/yuin/goldmark/text"
 )
 
 // --- HeadingLine ---
@@ -270,3 +271,78 @@ func TestExtractText_DirectTextNode(t *testing.T) {
 		return ast.WalkContinue, nil
 	})
 }
+
+// TestHeadingLine_WalkDescendsIntoNonTextChild exercises the ast.Walk path in
+// HeadingLine for headings where Lines() is empty (e.g. synthetic nodes).
+// The walk must descend through a non-text child (Emphasis) to reach the Text.
+func TestHeadingLine_WalkDescendsIntoNonTextChild(t *testing.T) {
+	src := []byte("Text\n\n## end\n")
+	// "end" starts at byte offset 9 (line 3).
+	f, err := lint.NewFile("test.md", src)
+	require.NoError(t, err)
+
+	heading := ast.NewHeading(2) // no Lines() set
+	emph := ast.NewEmphasis(1)
+	txt := ast.NewText()
+	txt.Segment = text.NewSegment(9, 12)
+	emph.AppendChild(emph, txt)
+	heading.AppendChild(heading, emph)
+
+	assert.Equal(t, 3, HeadingLine(heading, f))
+}
+
+// --- HeadingText and ExtractText additional cases ---
+
+func TestHeadingText_LinkText(t *testing.T) {
+	src := []byte("# [mdsmith](https://example.com)\n")
+	f, err := lint.NewFile("test.md", src)
+	require.NoError(t, err)
+
+	found := false
+	_ = ast.Walk(f.AST, func(n ast.Node, entering bool) (ast.WalkStatus, error) {
+		if !entering {
+			return ast.WalkContinue, nil
+		}
+		if h, ok := n.(*ast.Heading); ok {
+			found = true
+			assert.Equal(t, "mdsmith", HeadingText(h, f.Source))
+			return ast.WalkStop, nil
+		}
+		return ast.WalkContinue, nil
+	})
+	require.True(t, found)
+}
+
+func TestExtractText_LinkNode(t *testing.T) {
+	src := []byte("# [mdsmith](https://example.com)\n")
+	f, err := lint.NewFile("test.md", src)
+	require.NoError(t, err)
+
+	found := false
+	_ = ast.Walk(f.AST, func(n ast.Node, entering bool) (ast.WalkStatus, error) {
+		if !entering {
+			return ast.WalkContinue, nil
+		}
+		if h, ok := n.(*ast.Heading); ok {
+			link, ok2 := h.FirstChild().(*ast.Link)
+			require.True(t, ok2)
+			var buf bytes.Buffer
+			ExtractText(link, f.Source, &buf)
+			assert.Equal(t, "mdsmith", buf.String())
+			found = true
+			return ast.WalkStop, nil
+		}
+		return ast.WalkContinue, nil
+	})
+	require.True(t, found)
+}
+
+func TestHeadingText_AndExtractText_NoChildren(t *testing.T) {
+	h := ast.NewHeading(1)
+	assert.Equal(t, "", HeadingText(h, nil))
+
+	var buf bytes.Buffer
+	emptyLink := ast.NewLink()
+	ExtractText(emptyLink, nil, &buf)
+	assert.Equal(t, "", buf.String())
+}

internal/rules/blanklinearoundheadings/rule_coverage_test.go

@@ -165,6 +165,18 @@ func TestFix_Heading_InsertsBlankLines(t *testing.T) {
 	assert.Contains(t, string(result), "\n\nmore text")
 }
 
+// --- headingLastLine fallback ---
+
+func TestHeadingLastLine_NoLines_FallsBackToAstutil(t *testing.T) {
+	// Synthetic heading with no Lines() set exercises the fallback branch
+	// in headingLastLine that delegates to astutil.HeadingLine.
+	heading := ast.NewHeading(1)
+	f, err := lint.NewFile("test.md", []byte("# X\n"))
+	require.NoError(t, err)
+	last := headingLastLine(heading, f)
+	assert.Equal(t, 1, last)
+}
+
 // --- Category ---
 
 func TestCategory(t *testing.T) {

internal/rules/paragraphreadability/rule.go

@@ -142,5 +142,4 @@ func (r *Rule) DefaultSettings() map[string]any {
 	}
 }
 
-// isTable returns true if the paragraph's first line starts with a pipe,
 var _ rule.Configurable = (*Rule)(nil)

internal/rules/paragraphstructure/rule.go

@@ -135,5 +135,4 @@ func (r *Rule) DefaultSettings() map[string]any {
 	}
 }
 
-// isTable returns true if the paragraph's first line starts with a pipe,
 var _ rule.Configurable = (*Rule)(nil)