diff --git a/core/src/SaveIntegrity.cpp b/core/src/SaveIntegrity.cpp
new file mode 100644
index 0000000..1387ee7
--- /dev/null
+++ b/core/src/SaveIntegrity.cpp
@@ -0,0 +1,161 @@
+#include "vf/SaveIntegrity.h"
+
+#include <algorithm>
+#include <array>
+
+#include "vf/Block.h"
+#include "vf/Region.h"
+
+namespace vf {
+
+namespace {
+
+std::string decimal(long long value) { return std::to_string(value); }
+
+std::string coordText(const Vec3i& coord) {
+    return "(" + decimal(coord.x) + ", " + decimal(coord.y) + ", " + decimal(coord.z) + ")";
+}
+
+uint64_t mixBits(uint64_t value) {
+    value += 0x9E3779B97F4A7C15ull;
+    value = (value ^ (value >> 30)) * 0xBF58476D1CE4E5B9ull;
+    value = (value ^ (value >> 27)) * 0x94D049BB133111EBull;
+    return value ^ (value >> 31);
+}
+
+uint64_t latticeHash(uint64_t seed, int gx, int gz) {
+    uint64_t h = seed;
+    h = mixBits(h ^ (static_cast<uint64_t>(static_cast<uint32_t>(gx)) * 0x2545F4914F6CDD1Dull));
+    h = mixBits(h ^ (static_cast<uint64_t>(static_cast<uint32_t>(gz)) * 0x9E3779B97F4A7C15ull));
+    return h;
+}
+
+int latticeHeight(uint64_t seed, int gx, int gz) {
+    return 32 + static_cast<int>(latticeHash(seed, gx, gz) % 33ull);
+}
+
+struct SectorSpan {
+    uint32_t first = 0;
+    uint32_t last = 0;
+    int entryIndex = -1;
+};
+
+IntegrityIssue makeIssue(IntegrityIssueKind kind, IssueSeverity severity, std::size_t byteOffset,
+                         std::string detail) {
+    IntegrityIssue issue;
+    issue.kind = kind;
+    issue.severity = severity;
+    issue.byteOffset = byteOffset;
+    issue.detail = std::move(detail);
+    return issue;
+}
+
+bool actionOutranks(RepairActionKind candidate, RepairActionKind existing) {
+    auto rank = [](RepairActionKind kind) {
+        switch (kind) {
+            case RepairActionKind::RecomputeChecksum: return 0;
+            case RepairActionKind::RegenerateChunk: return 1;
+            case RepairActionKind::RemoveOrphanEntry: return 2;
+            case RepairActionKind::DropChunk: return 3;
+            case RepairActionKind::TruncateBuffer: return 4;
+        }
+        return 0;
+    };
+    return rank(candidate) > rank(existing);
+}
+
+} // namespace
+
+const char* issueSeverityName(IssueSeverity severity) {
+    switch (severity) {
+        case IssueSeverity::Info: return "info";
+        case IssueSeverity::Warning: return "warning";
+        case IssueSeverity::Recoverable: return "recoverable";
+        case IssueSeverity::Fatal: return "fatal";
+    }
+    return "unknown";
+}
+
+const char* integrityIssueName(IntegrityIssueKind kind) {
+    switch (kind) {
+        case IntegrityIssueKind::BadMagic: return "badMagic";
+        case IntegrityIssueKind::UnknownVersion: return "unknownVersion";
+        case IntegrityIssueKind::MalformedHeader: return "malformedHeader";
+        case IntegrityIssueKind::TruncatedBuffer: return "truncatedBuffer";
+        case IntegrityIssueKind::ChunkCountOverrun: return "chunkCountOverrun";
+        case IntegrityIssueKind::OrphanEntry: return "orphanEntry";
+        case IntegrityIssueKind::OverlappingEntries: return "overlappingEntries";
+        case IntegrityIssueKind::ChunkOutsideRegion: return "chunkOutsideRegion";
+        case IntegrityIssueKind::ChunkHeightOutOfRange: return "chunkHeightOutOfRange";
+        case IntegrityIssueKind::MalformedRecord: return "malformedRecord";
+        case IntegrityIssueKind::PaletteIndexOutOfRange: return "paletteIndexOutOfRange";
+        case IntegrityIssueKind::ChecksumMismatch: return "checksumMismatch";
+        case IntegrityIssueKind::LightingInconsistent: return "lightingInconsistent";
+        case IntegrityIssueKind::TrailingBytes: return "trailingBytes";
+    }
+    return "unknown";
+}
+
+const char* repairActionName(RepairActionKind kind) {
+    switch (kind) {
+        case RepairActionKind::DropChunk: return "dropChunk";
+        case RepairActionKind::TruncateBuffer: return "truncateBuffer";
+        case RepairActionKind::RecomputeChecksum: return "recomputeChecksum";
+        case RepairActionKind::RegenerateChunk: return "regenerateChunk";
+        case RepairActionKind::RemoveOrphanEntry: return "removeOrphanEntry";
+    }
+    return "unknown";
+}
+
+bool IntegrityReport::fatal() const {
+    for (const IntegrityIssue& issue : issues)
+        if (issue.severity == IssueSeverity::Fatal) return true;
+    return false;
+}
+
+bool IntegrityReport::repairable() const {
+    if (fatal()) return false;
+    for (const IntegrityIssue& issue : issues)
+        if (issue.severity == IssueSeverity::Recoverable) return true;
+    return false;
+}
+
+std::size_t IntegrityReport::countOf(IntegrityIssueKind kind) const {
+    std::size_t total = 0;
+    for (const IntegrityIssue& issue : issues)
+        if (issue.kind == kind) ++total;
+    return total;
+}
+
+std::size_t IntegrityReport::countAtLeast(IssueSeverity severity) const {
+    std::size_t total = 0;
+    for (const IntegrityIssue& issue : issues)
+        if (issue.severity >= severity) ++total;
+    return total;
+}
+
+const IntegrityIssue* IntegrityReport::firstOf(IntegrityIssueKind kind) const {
+    for (const IntegrityIssue& issue : issues)
+        if (issue.kind == kind) return &issue;
+    return nullptr;
+}
+
+const RepairAction* RepairPlan::forEntry(int entryIndex) const {
+    for (const RepairAction& action : actions)
+        if (action.entryIndex == entryIndex) return &action;
+    return nullptr;
+}
+
+std::size_t RepairPlan::countOf(RepairActionKind kind) const {
+    std::size_t total = 0;
+    for (const RepairAction& action : actions)
+        if (action.kind == kind) ++total;
+    return total;
+}
+
+int regeneratedSurfaceHeight(uint64_t seed, int worldX, int worldZ) {
+    int gx = floorDiv(worldX, chunkSize);
+    int gz = floorDiv(worldZ, chunkSize);
+    int fx = floorMod(worldX, chunkSize);
+    int fz = floorMod(worldZ, chunkSize);
+