It looks like this only fails with sufficiently long chains. On main, with this change, the test passes for me with 300 iterations but I get lots of os error 16 with 1000 iterations.

-        let (_, new_chain_id) = faucet_client
-            .open_chain(faucet_chain, None, Amount::ONE)
+        faucet_client
+            .open_chain(faucet_chain, Some(PublicKey::test_key(1)), Amount::ONE)
             .await?;
-        faucet_client.forget_chain(new_chain_id).await?;

I think the problem may be that in linera/main.rs, when handling OpenChain, we always add the new chain to the wallet. There, too, we should probably only do that if we have the secret key.

Adding forget_chain back does indeed solve it for me, despite the test_key(1). So the problem seems to be that the faucet fails to start up if it has 1000 chains in its wallet.