docs(requiredstructure): correct extractHeadings caller list in doc comments

checkSync never calls extractHeadings — it receives docHeadings as a
parameter. The actual 4th call site (parseSchemaWithRootFS) parses an
ephemeral schema-content File built fresh per call, so it doesn't
benefit from the memo the way the document-File call sites do.
Caught by code review round 1.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BTLNzEVChZtqSc7m7ph5Ah

Author: claude

internal/rules/requiredstructure/rule.go

@@ -1874,11 +1874,14 @@ type docHeading struct {
 }
 
 // extractHeadings walks the AST and collects all headings. Memoized
-// per File via lint.File.MemoFile: a composed schema calls this once
-// per extends source (bodySyncDiagnostics) plus from
-// checkSingleFileSchemaFromData, checkSync, and fixBodySyncIn, so a
-// document referencing N schema sources would otherwise re-walk the
-// same AST N+ times per Check.
+// per File via lint.File.MemoFile: on the document File, this is
+// called from checkSingleFileSchemaFromData, the per-source loop in
+// checkComposedSources (via bodySyncDiagnostics), and fixBodySyncIn,
+// so a document validated against a composed schema with N extends
+// sources would otherwise re-walk the same AST N+ times per Check.
+// parseSchemaWithRootFS also calls this, but on a throwaway
+// schema-content File built fresh per call, so the memo there is a
+// no-op rather than a shared cache.
 func extractHeadings(f *lint.File) []docHeading {
 	return f.MemoFile("requiredstructure.docHeadings", buildDocHeadings).([]docHeading)
 }

internal/rules/requiredstructure/rule_test.go

@@ -2006,8 +2006,8 @@ func TestHeadingText_WithLink(t *testing.T) {
 // TestExtractHeadings_Memoized pins that repeated calls on the same
 // File share the same backing slice: a composed schema with N extends
 // sources calls extractHeadings once per source (bodySyncDiagnostics)
-// plus once from checkSingleFileSchemaFromData/checkSync/fixBodySyncIn,
-// so an unmemoized walk re-scans the same AST N+ times per Check.
+// plus once from checkSingleFileSchemaFromData/fixBodySyncIn, so an
+// unmemoized walk re-scans the same AST N+ times per Check.
 func TestExtractHeadings_Memoized(t *testing.T) {
 	f := newTestFile(t, "doc.md", "# H1\n\n## H2\n\n### H3\n")
 	h1 := extractHeadings(f)