refactor(app): one idle-loop wake predicate for background results

hasPendingRPCResults() becomes hasPendingBackgroundResults(): the one
check the idle loop makes, every <= 200 ms, for work that finished on a
background thread and still has to be applied by update(). Lanes added
later put their term there. It still covers only the two RPC worker
lanes; no behaviour change.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/app.cpp

@@ -7432,7 +7432,7 @@ void App::verifyDebugCredential(const std::string& secret, std::function<void(bo
     cb(true);
 }
 
-bool App::hasPendingRPCResults() const {
+bool App::hasPendingBackgroundResults() const {
     return (worker_ && worker_->hasPendingResults())
         || (fast_worker_ && fast_worker_->hasPendingResults());
 }

src/app.h

@@ -738,8 +738,11 @@ public:
     bool debugGateRequiresAuth() const;
     void verifyDebugCredential(const std::string& secret, std::function<void(bool)> cb);
 
-    /// @brief Check if RPC worker has queued results waiting to be processed
+    /// @brief Something finished on a background thread and waits for update() to apply it on the main thread
-    bool hasPendingRPCResults() const;
+    /// (the RPC worker lanes). main.cpp's idle loop polls this every <= 200 ms (hasImmediateWork) and renders a
+    /// frame when it is true, so the result shows without input, even while the window is hidden. A new lane whose
+    /// results are applied in update() adds its term HERE.
+    bool hasPendingBackgroundResults() const;
     bool hasTransactionSendProgress() const { return send_progress_active_ || send_submissions_in_flight_ > 0 || !pending_opids_.empty(); }
     std::string transactionSendProgressText() const;
     std::string transactionRefreshProgressText() const;

src/main.cpp

@@ -1737,9 +1737,9 @@ int main(int argc, char* argv[])
                 auto sinceLast = std::chrono::duration_cast<std::chrono::milliseconds>(
                                      now - lastPeriodicFrame).count();
 
-                // Immediate triggers: async RPC results, visible notifications, work in progress
+                // Immediate triggers: background results, visible notifications, work in progress
                 // (also what keeps a hidden or occluded window responsive: ~5 fps while it lasts)
-                bool hasImmediateWork = app.hasPendingRPCResults()
+                bool hasImmediateWork = app.hasPendingBackgroundResults()
                                      || app.hasTransactionSendProgress()
                                      || app.isTransactionRefreshInProgress()
                                      || app.isShuttingDown()