async parsing + tex caching

Plugins/ZShell/Llm/segment.hpp

@@ -92,7 +92,9 @@ class LlmSegment : public QObject {
 
 	private:
 	void scheduleMarkdown();
-	void parseMarkdown();
+	// Kicks off an off-thread parse; returns false when one is already
+	// in flight (the pending change is picked up when it completes).
+	bool parseMarkdown();
 
 	Type m_type;
 	qint64 m_timestamp;
@@ -108,6 +110,7 @@ class LlmSegment : public QObject {
 	QVariantList m_markdown;
 	QTimer m_markdownTimer;
 	bool m_markdownDirty = false;
+	bool m_parseInFlight = false;
 };
 
 } // namespace ZShell::llm