6-phase, 16-task plan covering: canvas card scroll + fullscreen modal, InfoTip component + tooltip replacements in all 3 NodeForm components, answer stub type system (types → AnswerStubCard → TreeCanvas wiring → NodeList guard), backend draft/publish validation, markdown serializer compatibility, and session navigation defensive guard. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>