What it does
deki-json is a thin JSON-parsing module other modules pull in when they need to handle JSON at runtime (network responses, configuration blobs, etc.). On ESP32 it uses the ESP-IDF json component (cJSON); the desktop build links a comparable implementation.
The engine’s prefab format does not use JSON at runtime (it is MessagePack), so the editor and core do not depend on this module. It is only on the dependency path of modules that explicitly need JSON.