perf(node): throttle RPC polling during sync so block download isn't slowed

The full-node wallet polled the daemon at the per-tab cadence regardless of sync state.
On the Peers/Network tab that meant getpeerinfo every 5s + core every 5s + a full
transaction scan on every new block — and blocks arrive fast during sync. Each of those
calls takes the daemon's cs_main lock, the same lock block connection needs, so the node
synced noticeably slower than on the lightweight Console tab (core 10s, no peer polling).

Make the refresh cadence sync-aware:
- RefreshScheduler::kSyncProfile {core 10s, transactions/addresses/peers disabled} is applied
  to ALL tabs while state_.sync.syncing, and reverts to the per-tab profile when sync ends.
  applyRefreshPolicy() picks the profile; update() re-applies it on the syncing<->synced
  transition. This suppresses getpeerinfo and the per-block tx scan during sync (that data is
  incomplete mid-sync anyway) — every tab now syncs as fast as Console.
- collectCoreRefreshResult(rpc, includeBalance): skip z_gettotalbalance (wallet lock + cs_main)
  while syncing; only getblockchaininfo runs, which is also what drives sync-progress detection.
  applyCoreRefreshResult already leaves the balance untouched when balanceOk is false.

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

src/app.cpp

@@ -569,6 +569,12 @@ void App::update()
     // Wipe a secret (seed/private key) from the clipboard once its auto-clear delay elapses.
     pumpSecretClipboardClear();
 
+    // Re-apply the refresh cadence when sync starts/finishes: while syncing we throttle polling to
+    // a low-impact profile so RPC contention doesn't slow block download (see applyRefreshPolicy).
+    if (state_.sync.syncing != refresh_policy_syncing_) {
+        applyRefreshPolicy(current_page_);
+    }
+
     // Full-node RPC refreshes gate on ACTUAL RPC connectivity, not state_.connected. In lite
     // builds state_.connected is the lite-wallet "online" proxy (true when a wallet is open, to
     // enable the wallet UI), but there is no RPC daemon — so RPC polls (mining/balance/peers/txs)

src/app.h

@@ -519,6 +519,7 @@ private:
     int daemon_wait_attempts_ = 0;
     bool daemon_start_error_shown_ = false;
     int daemon_last_seen_crashes_ = 0;  // surface each new embedded-daemon crash reason once
+    bool refresh_policy_syncing_ = false;  // whether the sync-throttle refresh profile is active
     // Auto-clear for secrets copied to the clipboard. Only a hash of the copied secret is kept.
     std::uint64_t clipboard_secret_hash_ = 0;
     double clipboard_clear_deadline_ = 0.0;

src/app_network.cpp

@@ -664,7 +664,14 @@ App::RefreshIntervals App::getIntervalsForPage(ui::NavPage page)
 
 void App::applyRefreshPolicy(ui::NavPage page)
 {
-    network_refresh_.setIntervals(getIntervalsForPage(page));
+    // While the daemon is syncing, override the per-tab cadence with the low-impact sync profile so
+    // the wallet stops contending for the daemon's cs_main lock (frequent getpeerinfo / per-block
+    // transaction scans / balance polls slow block connection). This makes every tab sync as fast
+    // as the Console tab does today. Reverts to the per-tab profile once sync finishes.
+    refresh_policy_syncing_ = state_.sync.syncing;
+    network_refresh_.setIntervals(refresh_policy_syncing_
+        ? services::RefreshScheduler::kSyncProfile
+        : getIntervalsForPage(page));
 }
 
 bool App::currentPageNeedsWalletDataRefresh() const
@@ -1159,10 +1166,13 @@ void App::refreshCoreData()
                 ? fast_rpc_.get() : rpc_.get();
     if (!w || !rpc) return;
     ui::NavPage tracePage = current_page_;
+    // Skip the balance call while syncing (it's incomplete anyway and takes the wallet lock +
+    // cs_main). Captured on the main thread to avoid reading state_ off the worker thread.
+    const bool includeBalance = !state_.sync.syncing;
 
-    auto enqueued = network_refresh_.enqueue(services::NetworkRefreshService::Job::Core, *w, [this, rpc, tracePage]() -> rpc::RPCWorker::MainCb {
+    auto enqueued = network_refresh_.enqueue(services::NetworkRefreshService::Job::Core, *w, [this, rpc, tracePage, includeBalance]() -> rpc::RPCWorker::MainCb {
         AppRefreshRpcGateway refreshRpc(*rpc, traceSource(tracePage, "Core refresh"));
-        auto result = NetworkRefreshService::collectCoreRefreshResult(refreshRpc);
+        auto result = NetworkRefreshService::collectCoreRefreshResult(refreshRpc, includeBalance);
         return [this, result]() {
             try {
                 NetworkRefreshService::applyCoreRefreshResult(state_, result, std::time(nullptr));

src/services/network_refresh_service.cpp

@@ -284,18 +284,20 @@ NetworkRefreshService::CoreRefreshResult NetworkRefreshService::parseCoreRefresh
     return result;
 }
 
-NetworkRefreshService::CoreRefreshResult NetworkRefreshService::collectCoreRefreshResult(RefreshRpcGateway& rpc)
+NetworkRefreshService::CoreRefreshResult NetworkRefreshService::collectCoreRefreshResult(RefreshRpcGateway& rpc, bool includeBalance)
 {
     json totalBalance;
     json blockInfo;
     bool balanceOk = false;
     bool blockOk = false;
 
-    try {
-        totalBalance = rpc.call("z_gettotalbalance", json::array());
-        balanceOk = true;
-    } catch (const std::exception& e) {
-        DEBUG_LOGF("Balance error: %s\n", e.what());
+    if (includeBalance) {
+        try {
+            totalBalance = rpc.call("z_gettotalbalance", json::array());
+            balanceOk = true;
+        } catch (const std::exception& e) {
+            DEBUG_LOGF("Balance error: %s\n", e.what());
+        }
     }
 
     try {

src/services/network_refresh_service.h

@@ -230,7 +230,10 @@ public:
                                                     bool balanceOk,
                                                     const nlohmann::json& blockInfo,
                                                     bool blockOk);
-    static CoreRefreshResult collectCoreRefreshResult(RefreshRpcGateway& rpc);
+    // includeBalance=false skips z_gettotalbalance (which takes the wallet lock + cs_main) and only
+    // fetches getblockchaininfo — used while syncing, where the balance is incomplete anyway and the
+    // wallet should minimise lock contention with block connection.
+    static CoreRefreshResult collectCoreRefreshResult(RefreshRpcGateway& rpc, bool includeBalance = true);
     static MiningRefreshResult parseMiningRefreshResult(const nlohmann::json& miningInfo,
                                                         bool miningOk,
                                                         const nlohmann::json& localHashrate,

src/services/refresh_scheduler.h

@@ -34,6 +34,14 @@ public:
     static constexpr float kTxMaxAge = 15.0f;
     static constexpr float kOpidPoll = 2.0f;
 
+    // Low-impact polling profile applied while the daemon is SYNCING, regardless of the active tab.
+    // Only a slow progress poll runs (core, 10s); transactions/addresses/peers are disabled (0).
+    // Frequent getpeerinfo, per-block transaction scans, and balance polls all contend for the
+    // daemon's cs_main lock and measurably slow block connection during sync — this is exactly why
+    // the lightweight Console tab syncs faster than the Peers tab. Reverts to the per-tab profile
+    // once sync completes. (Tx/address/balance data is incomplete mid-sync anyway.)
+    static constexpr Intervals kSyncProfile{10.0f, 0.0f, 0.0f, 0.0f};
+
     static Intervals intervalsForPage(ui::NavPage page);
 
     void applyPage(ui::NavPage page);