dash-spv: CancellationToken ignored during DashSpvClient::start() — DNS discovery blocks shutdown

[lklimek]

Summary

DashSpvClient::run(token) calls self.start().await before entering the tokio::select! loop that monitors token.cancelled(). If start() blocks (e.g. during DNS peer discovery), cancelling the token has no effect until start() completes — the client cannot be stopped during its startup phase.

Steps to reproduce

1. Create a DashSpvClient for testnet with no explicit peers configured (no saved peers on disk either)
2. Call client.run(token)
3. After ~100ms, cancel the token
4. Observe that run() does not return within 10 seconds — it is stuck in DNS peer discovery inside PeerNetworkManager::start()

This was discovered via a unit test in dash-evo-tool (spv::tests::test_start_stop_clean_shutdown) that reliably times out.

Root cause

In src/client/sync_coordinator.rs:

pub async fn run(&self, token: CancellationToken) -> Result<()> {
    self.start().await?;  // ← blocks here, token not checked

    // Token is only checked AFTER start() completes:
    let error = loop {
        tokio::select! {
            // ...
            _ = token.cancelled() => { break None }
        };
    };
}

start() calls PeerNetworkManager::start() (src/network/manager.rs:143), which performs DNS peer discovery when no peers are available:

if peer_addresses.is_empty() {
    let dns_peers = self.discovery.discover_peers(self.network).await;  // ← no cancellation, no timeout
}

Suggested fix

Wrap self.start() in tokio::select! with the cancellation token:

pub async fn run(&self, token: CancellationToken) -> Result<()> {
    tokio::select! {
        result = self.start() => result?,
        _ = token.cancelled() => return Ok(()),
    }
    // ... monitoring loop
}

Optionally, PeerNetworkManager::start() could also accept a CancellationToken to make DNS discovery cancellation-aware at a finer granularity.

Priority

Low — only affects shutdown responsiveness during the initial connection phase. The monitoring loop handles cancellation correctly once startup completes.

_{🤖 Co-authored by Claudius the Magnificent AI Agent}