added basic network play

src/gameplay/coop/CoopGame.h

@@ -62,9 +62,13 @@ public:
     void setLevelUpCallback(LevelUpCallback cb) { levelUpCallback = cb; }
 
     void reset(int startLevel = 0);
+    void resetDeterministic(int startLevel, uint32_t seed);
     void tickGravity(double frameMs);
     void updateVisualEffects(double frameMs);
 
+    // Determinism / desync detection
+    uint64_t computeStateHash() const;
+
     // Per-player inputs -----------------------------------------------------
     void setSoftDropping(PlayerSide side, bool on);
     void move(PlayerSide side, int dx);
@@ -111,6 +115,8 @@ public:
 private:
     static constexpr double LOCK_DELAY_MS = 500.0;
 
+    void resetInternal(int startLevel_, const std::optional<uint32_t>& seedOpt);
+
     std::array<Cell, COLS * ROWS> board{};
     std::array<RowHalfState, ROWS> rowStates{};
     PlayerState left{};