Fix duplicate link-ref transformer in newParserInternal

Copilot review caught a real bug: goldmark.New() calls DefaultParser()
which already installs DefaultParagraphTransformers(), so the previous
goldmark.WithParserOptions(parser.WithParagraphTransformers(defaults...))
call appended a second link-reference transformer on top. The reset
closure only touched the appended instance; the one inside the default
parser kept pinning the last parsed document's bytes.

Build the parser explicitly with parser.NewParser (one set of block,
inline, and paragraph parsers including the lrp captured for reset)
and install it via goldmark.WithParser, then let goldmark.New's
extension Extend hooks register the additional block / inline parsers
they need. After this change there is exactly one link-ref transformer
in the resulting parser, and the closure returned to NewPooledParser
callers resets that instance.

https://claude.ai/code/session_0144ZKUS2Zrg7xBft54qyoti

Author: claude

pkg/markdown/flavor/parser.go

@@ -91,9 +91,12 @@ func newPooled(exts []goldmark.Extender) (parser.Parser, func()) {
 }
 
 // newParserInternal is the single goldmark.New call site in the tree.
-// It builds the canonical parser plus extracts the link-reference
-// paragraph transformer so pool callers can Reset its retained
-// document bytes.
+// It builds the canonical parser explicitly so the link-reference
+// paragraph transformer captured below is the same instance the
+// parser uses — and the only one. goldmark.New's own DefaultParser
+// would install a second link-ref transformer that the returned
+// reset closure could not reach, leaving pinned document bytes
+// alive in the pool slot.
 func newParserInternal(exts []goldmark.Extender) (parser.Parser, linkRefResetter) {
 	defaults := parser.DefaultParagraphTransformers()
 	var lrp linkRefResetter
@@ -103,15 +106,22 @@ func newParserInternal(exts []goldmark.Extender) (parser.Parser, linkRefResetter
 			break
 		}
 	}
-	md := goldmark.New(
-		goldmark.WithExtensions(exts...),
-		goldmark.WithParserOptions(
-			parser.WithAttribute(),
-			parser.WithBlockParsers(
+	p := parser.NewParser(
+		parser.WithBlockParsers(
+			append(parser.DefaultBlockParsers(),
 				markdown.PIBlockParserPrioritized(),
-			),
-			parser.WithParagraphTransformers(defaults...),
+			)...,
 		),
+		parser.WithInlineParsers(parser.DefaultInlineParsers()...),
+		parser.WithParagraphTransformers(defaults...),
+		parser.WithAttribute(),
+	)
+	// goldmark.New invokes each Extender's Extend(md) hook, which
+	// calls md.Parser().AddOptions(...) to register additional
+	// block / inline parsers on the parser installed by WithParser.
+	goldmark.New(
+		goldmark.WithParser(p),
+		goldmark.WithExtensions(exts...),
 	)
-	return md.Parser(), lrp
+	return p, lrp
 }