test: VM smoke and Lightning regtest suites

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/regtest-interactive.nix

@@ -0,0 +1,110 @@
+# regtest-interactive — turns the shared regtest stack into a friendly,
+# SSH-able dev VM (driven by `nix run .#regtest`).
+#
+# Layered on top of tests/regtest-node.nix + nix-bitcoin (see flake.nix).
+# Unlike the CI test's QEMU console / Python REPL, this gives you a real
+# terminal: copy/paste, scrollback, no log spam, landed straight in the
+# `operator` user with the CLIs preconfigured.
+{
+  config,
+  pkgs,
+  lib,
+  settings ? {
+    sshKeys = [ ];
+  },
+  ...
+}:
+let
+  # Fund LND on-chain and open an LND -> CLN channel, so you start with a
+  # working channel instead of building it by hand every session. Runs as
+  # operator (the CLIs are on its PATH); waits for the daemons first.
+  regtest-fund = pkgs.writeShellScriptBin "regtest-fund" ''
+    set -euo pipefail
+    echo "⏳ waiting for the lightning daemons..."
+    until lncli getinfo >/dev/null 2>&1 && lightning-cli getinfo >/dev/null 2>&1; do
+      sleep 2
+    done
+
+    echo "💰 funding LND on-chain..."
+    addr=$(lncli newaddress p2wkh | jq -r .address)
+    bitcoin-cli -rpcwallet=test sendtoaddress "$addr" 5 >/dev/null
+    mine=$(bitcoin-cli -rpcwallet=test getnewaddress)
+    bitcoin-cli -rpcwallet=test generatetoaddress 6 "$mine" >/dev/null
+    until [ "$(lncli walletbalance | jq -M '.confirmed_balance | tonumber')" -gt 0 ]; do
+      sleep 2
+    done
+
+    echo "🔗 opening LND -> CLN channel..."
+    cln=$(lightning-cli getinfo | jq -r .id)
+    lncli connect "$cln@127.0.0.1:9735" >/dev/null 2>&1 || true
+    lncli openchannel --node_key="$cln" --local_amt=1000000 >/dev/null
+    bitcoin-cli -rpcwallet=test generatetoaddress 6 "$mine" >/dev/null
+
+    echo "⏳ waiting for the channel to activate..."
+    until [ "$(lncli listchannels | jq '[.channels[] | select(.active)] | length')" -ge 1 ]; do
+      bitcoin-cli -rpcwallet=test generatetoaddress 1 "$mine" >/dev/null
+      sleep 2
+    done
+
+    echo "✓ channel active. Try:"
+    echo "    bolt11=\$(cln invoice 50000000 demo demo | jq -r .bolt11)"
+    echo "    lncli payinvoice --force \$bolt11"
+  '';
+in
+{
+  networking.hostName = "regtest";
+
+  # Throwaway VM — value is irrelevant, set only to silence the eval warning.
+  system.stateVersion = "24.11";
+
+  # SSH is the whole point — a clean terminal you can paste into.
+  services.openssh = {
+    enable = true;
+    settings.PasswordAuthentication = true;
+  };
+
+  # Land as `operator` (the nix-bitcoin user the CLIs are wired for).
+  # Simple shared password for a throwaway local VM with fake coins; also
+  # accept the adopter's SSH keys if settings.nix has any.
+  users.users.operator = {
+    password = "password"; # pragma: allowlist secret
+    extraGroups = [ "wheel" ];
+    openssh.authorizedKeys.keys = settings.sshKeys or [ ];
+  };
+  # Auto-login operator on the serial console too (if you skip SSH).
+  services.getty.autologinUser = "operator";
+
+  # Convenience aliases. `bitcoin-cli` already auto-selects the single
+  # loaded `test` wallet, but `btc` makes it explicit and short. We avoid
+  # aliasing `ln` (that's coreutils) — use the real `lncli`.
+  environment.shellAliases = {
+    btc = "bitcoin-cli -rpcwallet=test";
+    cln = "lightning-cli";
+  };
+
+  environment.systemPackages = [ regtest-fund ];
+
+  users.motd = ''
+
+    ┌─ Omnixient regtest dev VM ───────────────────────────────────┐
+      user: operator    password: password    (sudo enabled)
+      aliases:  btc  → bitcoin-cli -rpcwallet=test
+                cln  → lightning-cli       lncli → LND CLI
+      helper:   regtest-fund   fund LND + open an LND→CLN channel
+      nodes:    bitcoind(regtest)   CLN :9735   LND :9736
+      note: the stack pre-mines 110 blocks on boot — give it a few
+            seconds, then run `regtest-fund`.
+      quit: `exit`  (the VM is discarded)
+    └───────────────────────────────────────────────────────────┘
+  '';
+
+  # Headless + host:2222 -> guest:22 so `nix run .#regtest` can SSH in.
+  virtualisation.graphics = false;
+  virtualisation.forwardPorts = [
+    {
+      from = "host";
+      host.port = 2222;
+      guest.port = 22;
+    }
+  ];
+}