feat(wallet): migrate-to-seed, Phase 1 — isolated seed-wallet creation

First, fund-safe step of "migrate a legacy wallet to a seed wallet": mint a
brand-new BIP39 mnemonic wallet in an ISOLATED throwaway datadir so the user
can later sweep funds into it. No funds move and the real wallet.dat / main
daemon are never touched — the isolated node runs concurrently on its own port.

- EmbeddedDaemon: one-shot isolated-datadir override (setNextStartOverride)
  consumed on the next start(); a skip-default-port-check for an isolated
  instance beside the main daemon; and a tcpPortInUse() probe. The datadir's
  basename must be the assetchain name (DRAGONX) and the daemon reads
  <datadir>/DRAGONX.conf itself, so no -conf is passed (both learned from
  live testing against the hd-transparent-keys daemon).
- SeedWalletCreator (src/daemon): picks a free port, writes a throwaway conf,
  starts an isolated dragonxd with -usemnemonic=1 -connect=0, waits for RPC,
  calls z_exportmnemonic + z_getnewaddress (the sweep target), stops it, and
  keeps/scrubs the temp datadir. Off-thread; the seed is wiped after use.
- App: beginCreateSeedWallet (background) -> pumpSeedMigration (main-thread
  handoff) -> renderSeedMigrationDialog (Intro -> Working -> Show seed ->
  Error), reusing the seed_display grid + clipboard auto-clear.
- Settings: "Migrate to seed…" button (full-node gated) + persisted pending
  migration state (dest address + temp datadir) for Phase 2 to adopt.

Validated end-to-end against the hd-transparent-keys daemon: the isolated
node comes up in ~4s and returns a 24-word mnemonic + a shielded z-address.
Requires that daemon (the bundled Jun-28 build lacks z_exportmnemonic). The
migration modal uses English literals for now (as renderBackupDialog does);
the whole flow gets translated once Phase 2 finalizes it. Phase 2 (sweep +
adopt) is next.

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

src/daemon/seed_wallet_creator.cpp

@@ -0,0 +1,137 @@
+#include "daemon/seed_wallet_creator.h"
+
+#include <chrono>
+#include <filesystem>
+#include <thread>
+
+#include <sodium.h>
+
+#include "daemon/embedded_daemon.h"
+#include "rpc/rpc_client.h"
+#include "util/platform.h"
+
+namespace fs = std::filesystem;
+
+namespace dragonx {
+namespace daemon {
+
+namespace {
+
+// Random alphanumeric token for the isolated node's throwaway RPC credentials (libsodium CSPRNG;
+// sodium_init() has already run at app startup for the chat crypto).
+std::string randomToken(int n)
+{
+    static const char cs[] =
+        "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
+    std::string s;
+    s.reserve(n);
+    for (int i = 0; i < n; ++i)
+        s.push_back(cs[randombytes_uniform(sizeof(cs) - 1)]);
+    return s;
+}
+
+// A free localhost port for the isolated node — just above the default so it never collides with
+// the main daemon (which keeps running on the default port throughout).
+int pickFreePort()
+{
+    for (int p = 21770; p < 21900; ++p)
+        if (!EmbeddedDaemon::tcpPortInUse(p))
+            return p;
+    return 0;
+}
+
+}  // namespace
+
+SeedWalletResult SeedWalletCreator::create(bool keepDatadir,
+                                           const std::function<void(const std::string&)>& progress)
+{
+    auto report = [&](const std::string& m) { if (progress) progress(m); };
+    SeedWalletResult r;
+    std::error_code ec;
+
+    // 1. Isolated throwaway datadir. The Komodo/Hush daemon requires the datadir's basename to be
+    //    the assetchain name (DRAGONX) — mirroring ~/.hush/DRAGONX — or it mis-resolves its conf and
+    //    RPC port. So the wallet lives in <base>/DRAGONX; `base` is the migration root we clean up.
+    const std::string base = util::Platform::getConfigDir() + "/seed-migrate";
+    const std::string dataDir = base + "/DRAGONX";
+    fs::remove_all(base, ec);
+    fs::create_directories(dataDir, ec);
+    if (ec) { r.error = "Could not create the temporary wallet directory."; return r; }
+
+    // 2. Free port + fresh throwaway RPC credentials for the isolated node.
+    const int port = pickFreePort();
+    if (port <= 0) { r.error = "No free local port for the isolated node."; return r; }
+    const std::string user = randomToken(16);
+    const std::string pass = randomToken(32);
+
+    // 3. Minimal conf for the isolated node (own creds/port; -tls=only comes from the chain args,
+    //    so the RPC client below connects with TLS just like the main daemon does).
+    const std::string conf = "rpcuser=" + user + "\n"
+                             "rpcpassword=" + pass + "\n"
+                             "rpcport=" + std::to_string(port) + "\n"
+                             "server=1\n";
+    if (!util::Platform::writeFileAtomically(dataDir + "/DRAGONX.conf", conf,
+                                             /*restrictPermissions=*/true)) {
+        r.error = "Could not write the isolated node config.";
+        fs::remove_all(base, ec);
+        return r;
+    }
+
+    // 4. Start the isolated daemon: fresh mnemonic wallet (-usemnemonic=1), no network/sync.
+    report("Starting an isolated node…");
+    EmbeddedDaemon temp;
+    temp.setSkipPortCheck(true);  // runs on `port`, beside the main daemon on the default port
+    temp.setNextStartOverride(dataDir, {"-usemnemonic=1", "-connect=0", "-listen=0",
+                                        "-maxconnections=0"});
+    if (!temp.start("")) {
+        r.error = "Could not start the isolated node: " + temp.getLastError();
+        fs::remove_all(base, ec);
+        return r;
+    }
+
+    // 5. Connect to it, retrying until the RPC is responsive and past warmup.
+    report("Creating your new seed wallet…");
+    rpc::RPCClient cli;
+    bool ready = false;
+    for (int i = 0; i < 90 && !ready; ++i) {
+        if (cli.connect("127.0.0.1", std::to_string(port), user, pass, /*useTls=*/true)) {
+            try { cli.call("getinfo"); ready = true; }   // succeeds only once past warmup (-28)
+            catch (...) { cli.disconnect(); }
+        }
+        if (!ready) std::this_thread::sleep_for(std::chrono::seconds(1));
+    }
+    if (!ready) {
+        r.error = "The isolated node did not become ready in time.";
+        temp.stop(20000);
+        fs::remove_all(base, ec);
+        return r;
+    }
+
+    // 6. Export the new seed phrase + a fresh shielded receive address (the future sweep target).
+    try {
+        auto m = cli.call("z_exportmnemonic");
+        if (m.contains("mnemonic") && m["mnemonic"].is_string())
+            r.seedPhrase = m["mnemonic"].get<std::string>();
+        r.destAddress = cli.call("z_getnewaddress").get<std::string>();
+        r.ok = !r.seedPhrase.empty() && !r.destAddress.empty();
+        if (!r.ok) r.error = "The isolated node returned an empty seed or address.";
+    } catch (const std::exception& e) {
+        r.error = std::string("Seed export failed: ") + e.what();
+    }
+
+    // 7. Stop the isolated node (graceful; it flushes its tiny empty chain quickly).
+    cli.disconnect();
+    temp.stop(20000);
+
+    // 8. Keep the temp wallet for a later sweep/adopt step, or scrub it. tempDatadir is the
+    //    migration root `base`; the new wallet.dat lives in <base>/DRAGONX.
+    r.tempDatadir = base;
+    if (!keepDatadir || !r.ok) {
+        fs::remove_all(base, ec);
+        r.tempDatadir.clear();
+    }
+    return r;
+}
+
+}  // namespace daemon
+}  // namespace dragonx