The library charges per page

Severo’s memory lives in Firestore, and Firestore’s pricing has one axis that matters: reads and writes ▸ 9:09. His analogy earns the entry title: it’s like reading a book stored in a cloud library where every page is a separate file, finish a page, walk back to the desk, “oiga, ¿me regalas la siguiente página?”, and pay per trip ▸ 10:16. A teacher with memory naturally reads constantly, so the naive design, fetch every message, sum every token count on demand, “no es escalable, se me haría mucho el costo solamente por eso” ▸ 10:54. The fix is classic denormalization, derived on camera with Gemini: a user profile document that keeps running totals, one read where there were hundreds ▸ 11:51.

The deeper teaching is when to do this work, and it cuts against his own MVP instincts. Ship a single-language schema and fix it later? Later, “el problema es que ya hay usuarios usando la aplicación” ▸ 12:58: your options shrink to discarding their data or writing a converter that might corrupt it. So the rule he lands on distinguishes two kinds of change: structure must be right from the start; fields can be added forever ▸ 13:28.

el MVP puede ser feo; el esquema no, porque se congela con el primer usuario →

It’s a precise amendment to the ship-fast doctrine this diary preaches: cut every visible corner, the eyes, the animations, the languages, but not the invisible one, because pixels are repainted for free and data outlives its shape. The library charges per page; design so the teacher only ever needs to check out one book…