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.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
-    bool hasPendingRPCResults() const;
+    /// @brief Something finished on a background thread and waits for update() to apply it on the main thread
+    /// (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;