diff --git a/core/src/SaveMigration.cpp b/core/src/SaveMigration.cpp
new file mode 100644
index 0000000..5d3f103
--- /dev/null
+++ b/core/src/SaveMigration.cpp
@@ -0,0 +1,160 @@
+#include "vf/SaveMigration.h"
+
+#include <algorithm>
+#include <array>
+
+#include "vf/Anvil.h"
+#include "vf/Block.h"
+
+namespace vf {
+
+namespace {
+
+std::size_t divideUp(std::size_t value, std::size_t unit) {
+    return unit == 0 ? 0 : (value + unit - 1) / unit;
+}
+
+void putU32Be(std::vector<uint8_t>& out, uint32_t value) {
+    out.push_back(static_cast<uint8_t>((value >> 24) & 0xFFu));
+    out.push_back(static_cast<uint8_t>((value >> 16) & 0xFFu));
+    out.push_back(static_cast<uint8_t>((value >> 8) & 0xFFu));
+    out.push_back(static_cast<uint8_t>(value & 0xFFu));
+}
+
+uint32_t readU32Be(const uint8_t* at) {
+    return (static_cast<uint32_t>(at[0]) << 24) | (static_cast<uint32_t>(at[1]) << 16) |
+           (static_cast<uint32_t>(at[2]) << 8) | static_cast<uint32_t>(at[3]);
+}
+
+struct PayloadCursor {
+    const uint8_t* data;
+    std::size_t size;
+    std::size_t at = 0;
+    bool bad = false;
+
+    uint32_t u32() {
+        if (bad || at + 4 > size) {
+            bad = true;
+            return 0;
+        }
+        uint32_t value = readU32Be(data + at);
+        at += 4;
+        return value;
+    }
+    uint64_t u64() {
+        uint32_t high = u32();
+        uint32_t low = u32();
+        return (static_cast<uint64_t>(high) << 32) | static_cast<uint64_t>(low);
+    }
+    uint8_t u8() {
+        if (bad || at + 1 > size) {
+            bad = true;
+            return 0;
+        }
+        return data[at++];
+    }
+    bool take(std::size_t count, std::vector<uint8_t>& out) {
+        if (bad || at + count > size) {
+            bad = true;
+            return false;
+        }
+        out.assign(data + at, data + at + count);
+        at += count;
+        return true;
+    }
+    bool skip(std::size_t count) {
+        if (bad || at + count > size) {
+            bad = true;
+            return false;
+        }
+        at += count;
+        return true;
+    }
+};
+
+void writeU64Be(std::vector<uint8_t>& out, uint64_t value) {
+    putU32Be(out, static_cast<uint32_t>(value >> 32));
+    putU32Be(out, static_cast<uint32_t>(value & 0xFFFFFFFFull));
+}
+
+void buildPalette(const Chunk& chunk, std::vector<Block>& palette, std::vector<uint32_t>& indices) {
+    std::array<int, static_cast<std::size_t>(Block::Count)> slotOf;
+    slotOf.fill(-1);
+    palette.clear();
+    indices.clear();
+    indices.reserve(chunkVolume);
+    for (Block block : chunk.raw()) {
+        int& slot = slotOf[static_cast<std::size_t>(block)];
+        if (slot < 0) {
+            slot = static_cast<int>(palette.size());
+            palette.push_back(block);
+        }
+        indices.push_back(static_cast<uint32_t>(slot));
+    }
+}
+
+std::string versionPair(SaveVersion from, SaveVersion to) {
+    return std::string(saveVersionName(from)) + " -> " + saveVersionName(to);
+}
+
+} // namespace
+
+const SaveChunkRecord* SaveContainer::find(const Vec3i& coord) const {
+    for (const SaveChunkRecord& record : chunks)
+        if (record.coord == coord) return &record;
+    return nullptr;
+}
+
+bool saveReadU32At(const uint8_t* data, std::size_t size, std::size_t at, uint32_t& out) {
+    if (at + 4 > size) return false;
+    out = readU32Be(data + at);
+    return true;
+}
+
+bool saveWriteU32At(uint8_t* data, std::size_t size, std::size_t at, uint32_t value) {
+    if (at + 4 > size) return false;
+    data[at + 0] = static_cast<uint8_t>((value >> 24) & 0xFFu);
+    data[at + 1] = static_cast<uint8_t>((value >> 16) & 0xFFu);
+    data[at + 2] = static_cast<uint8_t>((value >> 8) & 0xFFu);
+    data[at + 3] = static_cast<uint8_t>(value & 0xFFu);
+    return true;
+}
+
+bool isKnownSaveVersion(uint32_t version) { return version >= 1u && version <= 4u; }
+
+bool versionHasPalette(SaveVersion version) { return version >= SaveVersion::V2; }
+bool versionHasLight(SaveVersion version) { return version >= SaveVersion::V3; }
+bool versionHasChecksum(SaveVersion version) { return version >= SaveVersion::V3; }
+bool versionHasMetadata(SaveVersion version) { return version >= SaveVersion::V4; }
+
+const char* saveVersionName(SaveVersion version) {
+    switch (version) {
+        case SaveVersion::V1: return "v1";
+        case SaveVersion::V2: return "v2";
+        case SaveVersion::V3: return "v3";
+        case SaveVersion::V4: return "v4";
+    }
+    return "v?";
+}
+
+bool readSaveHeader(const uint8_t* data, std::size_t size, SaveHeader& out) {
+    if (size < saveHeaderBytes) return false;
+    out.magic = readU32Be(data + 0);
+    out.version = readU32Be(data + 4);
+    out.regionX = static_cast<int32_t>(readU32Be(data + 8));
+    out.regionZ = static_cast<int32_t>(readU32Be(data + 12));
+    out.chunkCount = readU32Be(data + 16);
+    out.sectorBytes = readU32Be(data + 20);
+    out.tableChecksum = readU32Be(data + 24);
+    return true;
+}
+
+std::size_t saveTableBytes(const SaveHeader& header) {
+    return static_cast<std::size_t>(header.chunkCount) * saveEntryBytes;
+}
+
+std::size_t saveHeaderSectors(const SaveHeader& header) {
+    if (header.sectorBytes == 0) return 0;
+    return divideUp(saveHeaderBytes + saveTableBytes(header), header.sectorBytes);
+}
+