1% is discarded (lost to the mint, apparently) when swapping a cashu token for a new API key

[SatsAndSports]

As this is connecting to my own node, and I therefore have the server logs, my LLM came up with a theory about why. I'll share the LLM's thoughts in a comment

I made a token with 4,096 with Minibits (a mint that doesn't charge any fees, PS: my node accepts Minibits), and then created an API key

then, I made one query via curl and that failed:

Also, some little bits of money randomly dissappear sometimes

I created a key with 4096 sats, and refunded it after one failed query, but the refund has only 4,054 sats

Here is the only prompt I sent with that one token:

curl -X POST "http://localhost:8000/v1/chat/completions" -H "Authorization: Bearer sk-60e8e7e697807619b4f12dbb35a6d60ff0b9dea9fd0d0b621e6dda4e74dcb216" -H "Content-Type: application/json" -d '{                            
    "model": "claude-opus-4-6",
    "messages": [                                    
      {"role":"system","content":"You are Routstr."},
      {"role":"user","content":"how many bitcoins are there?"}
    ]
  }'
{"detail":{"error":{"message":"Insufficient balance: 4505892 mSats required for this model. 4054000 available.","type":"insufficient_quota","code":"insufficient_balance"}},"request_id":"7e94cf06-398d-43cf-be15-2f96a6e91541"}

then I pressed the 'Refund and Delete key' button. It said "refund requested", but - IIRC - it didn't show me the key. So I had to use curl to (re-)request the refund and I finally got a refund, but 42 sats dissappeared in the process:

This is my own node running on my laptop, where I can therefore also see the node's logs. It doesn't have any balance, suggesting that the funds were lost (to the mint?) and not earned by the node:

[SatsAndSports]

My LLM thinks that 1% is being donated to the mint, specifically line 85 of routstr/wallet.py: