Investigate Blockchair 'bad-txns-inputs-spent' error during Zcash swaps

[coderabbitai]

Problem

During testing of Zcash Ledger support, swapping took multiple attempts to succeed due to Blockchair API errors.

Error Details

Blockchair returned the following error response:

{
    "data": null,
    "context": {
        "code": 400,
        "source": "R",
        "error": "Invalid transaction. Error: 18: bad-txns-inputs-spent",
        "market_price_usd": 428.95,
        "cache": {
            "live": true,
            "duration": 120,
            "since": "2025-12-10 12:19:15",
            "until": "2025-12-10 12:21:15",
            "time": null
        },
        "api": {
            "version": "2.0.95-ie",
            "last_major_update": "2022-11-07 02:00:00",
            "next_major_update": "2023-11-12 02:00:00",
            "documentation": "https://blockchair.com/api/docs",
            "notice": "Try out our new API v.3: https://3xpl.com/data"
        },
        "servers": "API4,ZEC6",
        "time": 0.0015649795532226562,
        "render_time": 0.0026700496673583984,
        "full_time": 0.004235029220581055,
        "request_cost": 1
    }
}

Context

The error "bad-txns-inputs-spent" (Error code 18) indicates that the transaction inputs were already spent, suggesting potential issues with UTXO management or transaction broadcasting/retry logic.

Investigation Needed

• Determine if this is a transient issue with Blockchair's API
• Review UTXO selection and management for Zcash transactions
• Check if retry logic is properly handling spent inputs
• Consider if we need better error handling or user feedback for this scenario

Related

• PR: feat: enable ledger support for zcash #11337
• Reported by: @gomesalexandre