Before reading this: I'd recommend skimming Part 3's "Parser" section and Part 4's summary to understand how the parser outputs a domain.Contract. This post assumes you already know the parser can turn .meph into a struct.
I. A Narrative Engine's Fourth Problem: How Do You Keep Behavior Stable?
The parser is written. But it's code that gets maintained long-term — requirements change, formats expand, bugs get fixed. Every change risks breaking existing behavior.
The tension here is: creators depend on stable behavior, while developers depend on freedom to change. If every code change requires manually testing every known scenario, the developer will fear refactoring. If you don't test, broken behavior reaches the creator — but the creator doesn't care that you refactored the parser.
The solution is to "freeze" parsing behavior: use a fixed set of contracts as watchdogs. After every change, automatically compare parse results against expectations.
