feat(core): add scheduled block-tick queue for delayed updates

core/include/vf/BlockTick.h

@@ -0,0 +1,59 @@
+#pragma once
+
+#include <cstdint>
+#include <functional>
+#include <vector>
+#include "World.h"
+#include "Block.h"
+
+namespace vf {
+
+struct ScheduledTick {
+    Vec3i pos;
+    int dueTick;
+    uint32_t sequence;
+};
+
+inline bool isFallingBlock(Block b) { return b == Block::Sand || b == Block::Gravel; }
+
+inline bool tryGrowGrass(World& world, const Vec3i& pos) {
+    if (world.blockAt(pos.x, pos.y, pos.z) != Block::Dirt) return false;
+    if (world.solidAt(pos.x, pos.y + 1, pos.z)) return false;
+    world.setBlock(pos.x, pos.y, pos.z, Block::Grass);
+    return true;
+}
+
+using RandomTickHook = std::function<void(World&, const Vec3i&, Block)>;
+
+class BlockTickScheduler {
+public:
+    explicit BlockTickScheduler(uint32_t seed = 1u, int randomTicksPerChunk = 3);
+
+    void schedule(const Vec3i& pos, int delayTicks);
+    void cancel(const Vec3i& pos);
+    bool isScheduled(const Vec3i& pos) const;
+
+    void setRandomTickHook(RandomTickHook hook) { randomTickHook = std::move(hook); }
+
+    std::vector<Vec3i> tick(World& world);
+
+    const std::vector<Vec3i>& lastRandomTicks() const { return randomTickPositions; }
+    int currentTick() const { return tickCounter; }
+    std::size_t pendingCount() const { return pending.size(); }
+
+private:
+    uint32_t nextRandom();
+    void fireScheduled(std::vector<Vec3i>& fired);
+    void sampleRandomTicks(World& world);
+    void applyGravity(World& world);
+
+    int tickCounter = 0;
+    uint32_t rngState;
+    int randomTicksPerChunk;
+    uint32_t sequenceCounter = 0;
+    std::vector<ScheduledTick> pending;
+    std::vector<Vec3i> randomTickPositions;
+    RandomTickHook randomTickHook;
+};
+
+} // namespace vf