Sats cost (cost_sats) not returned in x-cashu mode

[sh1ftred]

Problem

When using x-cashu mode, the cost_sats field is not returned in the usage response, even though it is returned in other payment modes.

Observed Behavior

The usage object includes cost in USD (via cost: 0.00025998) and cost details, but no cost_sats field:

{
  "usage": {
    "prompt_tokens": 1137,
    "completion_tokens": 111,
    "total_tokens": 1248,
    "cost": 0.00025998,
    "is_byok": false,
    "prompt_tokens_details": {...},
    "cost_details": {...},
    "completion_tokens_details": {...}
  }
}

Expected Behavior

In other modes, a cost_sats variable is returned by the backend alongside the USD cost.

Environment

• Mode: x-cashu
• Backend: routstr-core

Steps to Reproduce

1. Enable x-cashu payment mode
2. Make a request that returns usage information
3. Observe that cost_sats is missing from the response

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Reported via Nostr mention