NYM-1199: add read-only --bond-check to sandbox families smoke

Adds `--bond-check <address>` to report which node (nym-node / mixnode /
gateway, with node_id) an arbitrary account controls on the sandbox mixnet
contract — read-only, no state change. Used to confirm whether a candidate
account can act as the node operator for the invite/accept/kick flow.

Finding on sandbox: the family-owner accounts (n13nrrvw…, n18cuqlr…) control
no bonded node, so exercising the 6 member commands still needs an account
that controls a bonded node + its mnemonic.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

nym-wallet/src-tauri/examples/sandbox_families_smoke.rs

@@ -361,9 +361,58 @@ async fn poll_membership(client: &Client, node_id: NodeId, want: Option<NodeFami
     Err(format!("timed out waiting for membership = {want:?}").into())
 }
 
+/// Read-only: report which (if any) node an arbitrary account controls on the
+/// sandbox mixnet contract. Signing identity is irrelevant — these are queries.
+async fn bond_check(client: &Client, addr: &str) -> Smoke {
+    let account = AccountId::from_str(addr)?;
+    let nym_node = client.nyxd.get_owned_nymnode(&account).await?.details;
+    let legacy = client
+        .nyxd
+        .get_owned_mixnode(&account)
+        .await?
+        .mixnode_details;
+    let gateway = client.nyxd.get_owned_gateway(&account).await?.gateway;
+
+    println!("\n=== BOND CHECK: {addr} ===");
+    println!(
+        "mixnet contract: {}",
+        client
+            .nyxd
+            .mixnet_contract_address()
+            .map(|a| a.to_string())
+            .unwrap_or_default()
+    );
+    match (&nym_node, &legacy) {
+        (Some(d), _) => println!(
+            "✅ controls nym-node → node_id = {}",
+            d.bond_information.node_id
+        ),
+        (_, Some(m)) => println!(
+            "✅ controls legacy mixnode → node_id (mix_id) = {}",
+            m.bond_information.mix_id
+        ),
+        (None, None) => println!("❌ controls no nym-node and no mixnode"),
+    }
+    println!(
+        "   gateway: {}",
+        if gateway.is_some() {
+            "yes (gateways can't be family members)"
+        } else {
+            "none"
+        }
+    );
+    Ok(())
+}
+
 #[tokio::main]
 async fn main() -> Smoke {
-    let do_write = std::env::args().any(|a| a == "--write");
+    let args: Vec<String> = std::env::args().collect();
+    let do_write = args.iter().any(|a| a == "--write");
+    let bond_check_addr = args
+        .iter()
+        .position(|a| a == "--bond-check")
+        .and_then(|i| args.get(i + 1))
+        .cloned();
 
     let mnemonic = load_mnemonic()?;
     let network: NymNetworkDetails = WalletNetwork::SANDBOX.into();
@@ -376,6 +425,11 @@ async fn main() -> Smoke {
         client.nyxd.node_families_contract_address()
     );
 
+    if let Some(addr) = bond_check_addr {
+        bond_check(&client, &addr).await?;
+        return Ok(());
+    }
+
     read_smoke(&client).await?;
 
     if do_write {