perf(daemon): skip the UI-thread datadir lock wait

Starting the daemon polls for an already-running node holding the
datadir, sleeping up to three 100 ms intervals to let a shutting-down
node clear out. When a start runs on the UI thread, that is up to 300 ms
of blocking sleep on the render thread.

- The lock-wait poll count is now a parameter. A start invoked on the UI
  thread passes 0, which does a single check and never sleeps; every
  other caller keeps the three-poll wait. The default is unchanged, so
  background starts behave exactly as before.

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

src/app.cpp

@@ -5975,7 +5975,8 @@ bool App::startEmbeddedDaemon()
 
     // Only a process we actually launched starts a new story: a start that finds a node already running (and
     // launches nothing) must not wipe what the tracker knows about that node from its debug.log.
-    const bool launched = daemon_controller_->start(settings_.get());
+    const bool launched = daemon_controller_->start(
+        settings_.get(), std::this_thread::get_id() == ui_thread_id_ ? 0 : daemon::EmbeddedDaemon::kDatadirLockWaitMaxPolls);
     if (launched) resetDaemonBusy();   // a new process: whatever the last one was doing is over
     return launched;
 }

src/daemon/daemon_controller.cpp

@@ -41,10 +41,10 @@ void DaemonController::syncSettings(const config::Settings* settings)
     daemon_->setWalletFile(walletFile);
 }
 
-bool DaemonController::start(const config::Settings* settings)
+bool DaemonController::start(const config::Settings* settings, int lockWaitPolls)
 {
     syncSettings(settings);
-    return daemon_->start();
+    return daemon_->start("", lockWaitPolls);
 }
 
 void DaemonController::stop(int waitMs)

src/daemon/daemon_controller.h

@@ -95,7 +95,7 @@ public:
     void setStateCallback(StateCallback callback);
     void syncSettings(const config::Settings* settings);
 
-    bool start(const config::Settings* settings);
+    bool start(const config::Settings* settings, int lockWaitPolls = 3);
     void stop(int waitMs);
     void markStopRequested();
 

src/daemon/embedded_daemon.cpp

@@ -505,7 +505,7 @@ static bool isPortInUse(int port)
 #endif
 }
 
-bool EmbeddedDaemon::start(const std::string& binary_path)
+bool EmbeddedDaemon::start(const std::string& binary_path, int lockWaitPolls)
 {
     std::lock_guard<std::mutex> life(lifecycle_mutex_);
 
@@ -564,11 +564,10 @@ bool EmbeddedDaemon::start(const std::string& binary_path)
     // skip_port_check_ / -datadir override) are exempt; they run their own datadir+port.
     {
         constexpr int kDatadirLockWaitPollMs   = 100;
-        constexpr int kDatadirLockWaitMaxPolls = 3;   // ~300ms total, breaks early on exit
         bool stillRunning = false;
         if (!skip_port_check_ && override_datadir_.empty()) {
             stillRunning = isDaemonProcessRunning();
-            for (int i = 0; stillRunning && i < kDatadirLockWaitMaxPolls; ++i) {
+            for (int i = 0; stillRunning && i < lockWaitPolls; ++i) {
                 std::this_thread::sleep_for(std::chrono::milliseconds(kDatadirLockWaitPollMs));
                 stillRunning = isDaemonProcessRunning();
             }

src/daemon/embedded_daemon.h

@@ -61,7 +61,10 @@ public:
      * @return true if process started successfully (or is already running); false while a stop
      *         session (beginStop() .. endStop()) is still in progress
      */
-    bool start(const std::string& binary_path = "");
+    static constexpr int kDatadirLockWaitMaxPolls = 3;   // ~300ms total, breaks early on exit
+
+    /** @param lockWaitPolls max 100ms datadir-lock waits (0 = single check, never sleeps; for the UI thread) */
+    bool start(const std::string& binary_path = "", int lockWaitPolls = kDatadirLockWaitMaxPolls);
     
     /**
      * @brief Stop the daemon process this object launched (never any other dragonxd)