Scenario ChatGPT Pet: Update

Overview

An existing pet is its sprite sheet: a PNG or WebP the user downloaded from ChatGPT, a Codex pet folder (pet.json plus the sheet it names), or a Scenario asset id of a sheet made earlier. That file is the pet's identity here; there is no pet record to look up. The update never overwrites it: the result is a new package next to the run, with the same id and name unless the user changes them.