Electrum chain source omits the regtest fast-sync override applied to Esplora

[hash-money]

Summary

When ChainSource::Electrum is selected on Network::Regtest, the chain
source is configured with set_chain_source_electrum(url, None). This causes
ldk-node to fall back to its default BackgroundSyncConfig (80s on-chain,
30s lightning). The same configuration with ChainSource::Esplora on
Network::Regtest instead applies a 2s/2s/30s BackgroundSyncConfig.

Where

orange-sdk/src/lightning_wallet.rs:

match config.chain_source {
    ChainSource::Esplora { url, username, password } => {
        let sync_config = if config.network == Network::Regtest {
            ldk_node::config::EsploraSyncConfig {
                background_sync_config: Some(BackgroundSyncConfig {
                    onchain_wallet_sync_interval_secs: 2,
                    lightning_wallet_sync_interval_secs: 2,
                    fee_rate_cache_update_interval_secs: 30,
                }),
            }
        } else {
            ldk_node::config::EsploraSyncConfig::default()
        };
        // ... sync_config is passed into set_chain_source_esplora
    },
    ChainSource::Electrum(url) => builder.set_chain_source_electrum(url, None),
    // ^ no regtest-aware sync_config; passes None
    ChainSource::BitcoindRPC { .. } => { ... },
};

Effect

Regtest workflows using the Electrum chain source observe ~80s feedback
cycles for incoming on-chain detection, vs. the ~2s the Esplora regtest path
provides. ldk_node::Builder::set_chain_source_electrum accepts an
Option<ElectrumSyncConfig> with the same shape as EsploraSyncConfig, so
the override pattern already used a few lines above is directly portable.

Suggested fix

Mirror the Esplora regtest override on the Electrum arm:

ChainSource::Electrum(url) => {
    let sync_config = if config.network == Network::Regtest {
        Some(ldk_node::config::ElectrumSyncConfig {
            background_sync_config: Some(BackgroundSyncConfig {
                onchain_wallet_sync_interval_secs: 2,
                lightning_wallet_sync_interval_secs: 2,
                fee_rate_cache_update_interval_secs: 30,
            }),
        })
    } else {
        None
    };
    builder.set_chain_source_electrum(url, sync_config)
},

Mainnet behavior is unchanged — the else None branch preserves ldk-node
defaults. Happy to open a PR if useful.

Environment

• orange-sdk rev 2762df2
• ldk-node 0.7.0