perf(migrate): gate the seed-migration confirming balance scan

While the seed migration sits on the Confirming gate it polled the
sweep's confirmations and a full wallet balance together on every pass.
That balance call is the expensive one, and it only matters once the
sweep is mined and we do not yet have a post-mine figure, yet it ran
every poll even mid-sync when it cannot move the gate.

- The confirmation count is still read on every poll.
- The balance scan now runs only when it can actually advance the adopt
  gate: the sweep is mined, no post-mine balance has been recorded yet,
  and no sync is in progress. The manual Refresh button forces it
  regardless.
- The decision lives in a small pure helper, and the poller snapshots
  the main-thread state it needs rather than reading members off the
  worker thread.
- The Confirming screen now claims a leftover remainder (and offers the
  re-sweep button) only once the balance has actually been measured; while
  it is still unknown it keeps waiting instead of prompting on a sentinel.

Tests cover the gate helper across the forced, syncing, and mined cases.

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

src/app.cpp

@@ -5015,7 +5015,10 @@ void App::renderSeedMigrationDialog()
         if (confirmed && legacyEmpty) {
             if (ui::material::TactileButton(TR("mig_adopt"), ImVec2(180 * dp, 0)))
                 beginAdoptSeedWallet();
-        } else if (confirmed && !legacyEmpty) {
+        } else if (confirmed && seed_migration_legacy_remaining_ >= 0.0 && !legacyEmpty) {
+            // Only claim a remainder once the legacy balance was actually measured; while a sweep is
+            // mined but the balance scan is still gated (node syncing), remaining stays at the -1.0
+            // sentinel, so fall through to the waiting state rather than offering a sweep on an unknown.
             ImGui::PushStyleColor(ImGuiCol_Text, ui::material::ReadableError());
             ImGui::TextWrapped("%s", TR("mig_remainder"));
             ImGui::PopStyleColor();
@@ -5026,7 +5029,7 @@ void App::renderSeedMigrationDialog()
         }
         ImGui::SameLine();
         if (ui::material::TactileButton(TR("refresh"), ImVec2(110 * dp, 0)))
-            pollSweepStatus();
+            pollSweepStatus(/*forceBalance=*/true);
         ImGui::SameLine();
         if (ui::material::TactileButton(TR("mig_later"), ImVec2(100 * dp, 0)))
             close();  // pending state + txid persist; resumes here next time

src/app.h

@@ -1155,7 +1155,7 @@ private:
     // opid the daemon no longer knows (stale) -> back to the dismissable Sweep gate (re-check balance).
     std::function<void(bool, const std::string&)> makeSweepCompletionCallback(bool resumed);
     void beginSweepToSeedWallet();       // z_mergetoaddress ["ANY_TADDR","ANY_ZADDR"] -> dest
-    void pollSweepStatus();              // Confirming step: poll sweep confirmations + legacy balance
+    void pollSweepStatus(bool forceBalance = false);  // Confirming step: confs always; balance only when it can move the gate
     void locateSweepTxid();              // recover a lost sweep txid (send to dest) -> Confirming gate
     void beginAdoptSeedWallet();         // stop daemon -> swap wallet.dat -> restart with -rescan
     void provisionChatIdentityFromSecret(std::string secret);

src/app_network.cpp

@@ -33,6 +33,7 @@
 #include "rpc/rpc_client.h"
 #include "rpc/rpc_worker.h"
 #include "rpc/connection.h"
+#include "services/seed_migration_poll.h"   // migrationWantsBalanceScan: gate the Confirming balance scan
 #include "services/lowest_block_search.h"   // detectLowestAvailableBlockHeight: pure search + probe classification
 #include "chat/chat_identity.h"  // deriveChatIdentityFromSecret for HushChat identity provisioning
 #include "ui/windows/chat_tab.h"  // ui::ResetChatTab — wipe chat UI plaintext on a wallet switch
@@ -6338,30 +6339,36 @@ std::function<void(bool, const std::string&)> App::makeSweepCompletionCallback(b
 // adopt step is gated on the tx being mined (confs >= 1) AND the legacy balance being ~0, so we
 // never swap wallet.dat while the funds could still bounce back (dropped/reorged tx) or while a
 // remainder is left behind (a sweep too big for one transaction).
-void App::pollSweepStatus()
+void App::pollSweepStatus(bool forceBalance)
 {
     if (capture_mode_) return;  // no live ops during a UI sweep
     if (!rpc_ || !worker_ || !state_.connected) return;
     if (seed_migration_confirm_in_flight_ || seed_migration_sweep_txid_.empty()) return;
     seed_migration_confirm_in_flight_ = true;
     const std::string txid = seed_migration_sweep_txid_;
-    worker_->post([this, txid]() -> rpc::RPCWorker::MainCb {
-        int confs = 0; double remaining = -1.0; bool ok = false;
+    // Snapshot main-thread state for the worker - never read members off the worker thread.
+    const bool syncing = effectivelySyncing();
+    const double priorRemaining = seed_migration_legacy_remaining_;
+    worker_->post([this, txid, forceBalance, syncing, priorRemaining]() -> rpc::RPCWorker::MainCb {
+        int confs = 0; double remaining = -1.0; bool ok = false; bool scanned = false;
         rpc::RPCClient::TraceScope trace("Migrate / confirm");
         try {
             auto tx = rpc_->call("gettransaction", {txid});
             if (tx.contains("confirmations") && tx["confirmations"].is_number())
                 confs = tx["confirmations"].get<int>();
-            auto bal = rpc_->call("z_gettotalbalance");
-            if (bal.contains("total") && bal["total"].is_string())
-                remaining = std::stod(bal["total"].get<std::string>());
+            if (services::migrationWantsBalanceScan(forceBalance, syncing, confs, priorRemaining)) {
+                auto bal = rpc_->call("z_gettotalbalance");
+                if (bal.contains("total") && bal["total"].is_string())
+                    remaining = std::stod(bal["total"].get<std::string>());
+                scanned = true;
+            }
             ok = true;
         } catch (...) {}
-        return [this, confs, remaining, ok]() {
+        return [this, confs, remaining, ok, scanned]() {
             seed_migration_confirm_in_flight_ = false;
             if (ok) {
                 seed_migration_sweep_confs_ = confs;
-                seed_migration_legacy_remaining_ = remaining;
+                if (scanned) seed_migration_legacy_remaining_ = remaining;
             }
         };
     });

src/services/seed_migration_poll.h

@@ -0,0 +1,20 @@
+// DragonX Wallet - ImGui Edition
+// Copyright 2024-2026 The Hush Developers
+// Released under the GPLv3
+
+#pragma once
+
+namespace dragonx {
+namespace services {
+
+// The expensive z_gettotalbalance only changes the seed-migration adopt gate once the sweep is mined and
+// we have no post-mine figure yet (priorRemaining < 0). A manual Refresh forces it; an active sync
+// suppresses the automatic scan (the Refresh button still overrides).
+inline bool migrationWantsBalanceScan(bool forceBalance, bool syncing, int confs, double priorRemaining)
+{
+    if (forceBalance) return true;
+    return !syncing && confs >= 1 && priorRemaining < 0.0;
+}
+
+} // namespace services
+} // namespace dragonx