refactor: from guest threads to EE scheduler

ps2xRuntime/include/runtime/ps2_memory.h

@@ -204,20 +204,16 @@ struct GSRegisters
     uint64_t extdata;  // External data
     uint64_t extwrite; // External write
     uint64_t bgcolor;  // Background color
-    // Status. Concurrency contract: the vsync worker thread toggles the FIELD bit
-    // (bit 13) once per tick; guest threads issue write-one-to-clear writes against
-    // the SIGNAL/FINISH status bits (0..1) via the MMIO path; the GIF sets SIGNAL
-    // and FINISH from yet another thread. All three interleave, so this register
-    // must be updated with atomic RMWs only (no load-then-store pairs anywhere).
+    // Status remains atomic because the renderer/UI can observe it while the
+    // single EE executor updates SIGNAL, FINISH and FIELD.
     std::atomic<uint64_t> csr;
+    std::atomic<uint64_t> vsyncTick;
     uint64_t imr;      // Interrupt mask
     uint64_t busdir;   // Bus direction
     uint64_t siglblid; // Signal label ID
 };
-static_assert(sizeof(GSRegisters) == (19u * sizeof(uint64_t)), "GSRegisters layout changed unexpectedly");
+static_assert(sizeof(GSRegisters) == (20u * sizeof(uint64_t)), "GSRegisters layout changed unexpectedly");
 static_assert(alignof(GSRegisters) == alignof(uint64_t), "GSRegisters alignment must remain 64-bit");
-// CSR is written by the vsync worker while guest threads concurrently read/write it
-// (MMIO) and the GIF sets SIGNAL/FINISH; a lock-free atomic keeps that path wait-free.
 static_assert(std::atomic<uint64_t>::is_always_lock_free, "GS CSR atomic must be lock-free on all supported targets");
 
 // PS2 VIF (VPU Interface) registers