world loading memory pressure detector

Signed-off-by: Pavel Okhlopkov <pavel.okhlopkov@flant.com>

include/core/memory_monitor.hpp

@@ -34,10 +34,17 @@ public:
     size_t getRecommendedCacheBudget() const;
 
     /**
-     * Check if system is under memory pressure
+     * Check if system is under memory pressure (< 10% RAM available)
      */
     bool isMemoryPressure() const;
 
+    /**
+     * Check if system is under severe memory pressure (< 15% RAM available).
+     * At this level, background loading should pause entirely until memory
+     * is freed — continuing to allocate risks OOM-killing other applications.
+     */
+    bool isSevereMemoryPressure() const;
+
 private:
     MemoryMonitor() = default;
     size_t totalRAM_ = 0;

include/rendering/terrain_manager.hpp

@@ -366,6 +366,11 @@ private:
     std::condition_variable queueCV;
     std::deque<TileCoord> loadQueue;
     std::queue<std::shared_ptr<PendingTile>> readyQueue;
+    // Maximum number of prepared-but-not-finalized tiles in readyQueue.
+    // Each prepared tile can hold 100–500 MB of decoded textures in RAM.
+    // Workers sleep when this limit is reached, letting the main thread
+    // finalize (GPU-upload + free) before more tiles are prepared.
+    static constexpr size_t maxReadyQueueSize_ = 3;
 
     // In-RAM tile cache (LRU) to avoid re-reading from disk
     struct CachedTile {