file_sys: add a deterministic NUP packer, Convert to NUP in Qt and eden-cli --pack-nup (#271)

* file_sys: add a NUP packer for loose dumps

Packs a loose dump (exefs/romfs, base/, updates/<version>/ and
dlc/<titleid>/<n>/) into a NUP v1 container with the aligned record
layout. Every package is kept, files are deduplicated by SHA-256 and
compressed with zstd unless that does not shrink them, and files over
256 MiB are stored raw.

Output is byte-identical on every platform: compression is
single-threaded with every frame parameter set explicitly, and zstd is
always bundled so all builds use the same version.

A low-storage mode deletes each source file once its extent is synced
and journaled, and an interrupted run resumes from the journal.

Assisted-by: Claude Opus 5.5 (wrote the packer, its EdenPack-free dump detection, the aligned record layout and the deterministic zstd setup; ran the Raiders and Donkey Kong Bananza packs and boot checks)

* tests: cover the NUP packer

Round-trips a dump through NupContainer, checks standalone updates, a
bare exefs/romfs dump, low-storage resume and overwrite rejection, and
pins the hash of a packed dump so changes to the output are deliberate.

Assisted-by: Claude Opus 5.5 (wrote the tests, including the pinned output hash)

* qt: add Convert to NUP to the game list

Shown for loose dumps. Asks for confirmation with the estimated space,
offers low-storage mode, runs in the background with progress and
cancel, and resumes an interrupted low-storage conversion.

Assisted-by: Claude Opus 5.5 (wrote the Convert to NUP action and its progress and resume handling)

* cli: add --pack-nup <dump> [out.nup]

Assisted-by: Claude Opus 5.5 (wrote the --pack-nup option)

12 files changed, 2156 insertions, 1 deletions

diff --git a/src/core/CMakeLists.txt b/src/core/CMakeLists.txt
index 846ea7a25d..fd45642876 100644
--- a/src/core/CMakeLists.txt
+++ b/src/core/CMakeLists.txt
@@ -134,6 +134,8 @@ add_library(core STATIC
     file_sys/registered_cache.h
     file_sys/nup_container.cpp
     file_sys/nup_container.h
+    file_sys/nup_writer.cpp
+    file_sys/nup_writer.h
     file_sys/romfs.cpp
     file_sys/romfs.h
     file_sys/romfs_factory.cpp
diff --git a/src/core/file_sys/nup_writer.cpp b/src/core/file_sys/nup_writer.cpp
new file mode 100644
index 0000000000..8c7728ed01
--- /dev/null
+++ b/src/core/file_sys/nup_writer.cpp
@@ -0,0 +1,1459 @@
+// SPDX-FileCopyrightText: Copyright 2026 Eden Emulator Project
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#include "core/file_sys/nup_writer.h"
+
+#include <algorithm>
+#include <array>
+#include <cctype>
+#include <charconv>
+#include <cstring>
+#include <limits>
+#include <map>
+#include <memory>
+#include <optional>
+#include <span>
+#include <stdexcept>
+#include <unordered_map>
+#include <unordered_set>
+#include <vector>
+
+#include <nlohmann/json.hpp>
+#include <openssl/evp.h>
+#include <zstd.h>
+
+#include "common/fs/file.h"
+#include "common/fs/path_util.h"
+#include "core/file_sys/control_metadata.h"
+#include "core/file_sys/vfs/vfs_real.h"
+#include "core/loader/deconstructed_rom_directory.h"
+
+namespace FileSys::Nup {
+namespace {
+
+using Json = nlohmann::json;
+namespace fs = std::filesystem;
+
+constexpr std::array<u8, 4> Magic{'N', 'U', 'P', 0x01};
+constexpr std::array<u8, 4> TocMagic{'T', 'O', 'C', 0x01};
+constexpr u64 SuperblockSize = 0x80;
+constexpr u64 TocHeaderSize = 0x30;
+constexpr u64 PackageRecordSize = 0x40;
+constexpr u64 DirRecordSize = 0x18;
+constexpr u64 FileRecordSize = 0x50;
+constexpr u64 ExtentAlignment = 16;
+constexpr u32 NoDir = 0xFFFFFFFF;
+
+constexpr u8 KindBase = 0;
+constexpr u8 KindUpdate = 1;
+constexpr u8 KindAddon = 2;
+constexpr u8 FlagStandaloneUpdate = 0x01;
+constexpr u8 CodecRaw = 0;
+constexpr u8 CodecZstd = 1;
+
+constexpr u16 TlvNpdm = 0x0001;
+constexpr u16 TlvNacp = 0x0002;
+constexpr u16 TlvIcon = 0x0003;
+constexpr u16 TlvDisplayVersion = 0x0004;
+constexpr u16 TlvTitleName = 0x0005;
+constexpr u16 TlvPublisher = 0x0006;
+constexpr u16 TlvSourceDump = 0x0008;
+
+constexpr int JournalVersion = 1;
+constexpr u64 ProgressStep = 64ULL * 1024 * 1024;
+constexpr size_t MaxChunkFiles = 4096;
+constexpr size_t ReadBufferSize = 4 * 1024 * 1024;
+
+class PackError : public std::runtime_error {
+public:
+    PackError(PackResult result_, const std::string& message)
+        : std::runtime_error(message), result{result_} {}
+    PackResult result;
+};
+
+u64 AlignUp(u64 value, u64 alignment) {
+    return (value + alignment - 1) / alignment * alignment;
+}
+
+std::string ToUtf8(const fs::path& path) {
+    const auto u8 = path.generic_u8string();
+    return {u8.begin(), u8.end()};
+}
+
+fs::path FromUtf8(const std::string& value) {
+    return fs::path{std::u8string{value.begin(), value.end()}};
+}
+
+std::string Lower(std::string value) {
+    std::ranges::transform(value, value.begin(),
+                           [](unsigned char c) { return static_cast<char>(std::tolower(c)); });
+    return value;
+}
+
+fs::path WithSuffix(fs::path path, std::string_view suffix) {
+    path += suffix;
+    return path;
+}
+
+bool IsFile(const fs::path& path) {
+    std::error_code ec;
+    return fs::is_regular_file(path, ec);
+}
+
+fs::path FindDirectory(const fs::path& parent, std::string_view name) {
+    std::error_code ec;
+    if (parent.empty() || !fs::is_directory(parent, ec)) {
+        return {};
+    }
+    const auto wanted = Lower(std::string{name});
+    for (const auto& entry : fs::directory_iterator(parent, ec)) {
+        if (entry.is_directory(ec) && Lower(ToUtf8(entry.path().filename())) == wanted) {
+            return entry.path();
+        }
+    }
+    return {};
+}
+
+std::optional<u64> ParseDecimal(const std::string& name) {
+    u64 value{};
+    const auto* end = name.data() + name.size();
+    const auto [ptr, ec] = std::from_chars(name.data(), end, value);
+    if (name.empty() || ec != std::errc{} || ptr != end) {
+        return std::nullopt;
+    }
+    return value;
+}
+
+// The exefs folder a dump boots from: the newest updates/<version>, else base, else the root.
+// Each must hold main, main.npdm and a romfs folder next to it or under base.
+bool HasBootableExeFS(const fs::path& root) {
+    const auto bootable = [](const fs::path& exefs) {
+        return !exefs.empty() && IsFile(exefs / "main") && IsFile(exefs / "main.npdm");
+    };
+    fs::path exefs;
+    std::optional<u64> best_version;
+    if (const auto updates = FindDirectory(root, "updates"); !updates.empty()) {
+        std::error_code ec;
+        for (const auto& entry : fs::directory_iterator(updates, ec)) {
+            const auto version = ParseDecimal(ToUtf8(entry.path().filename()));
+            const auto candidate = FindDirectory(entry.path(), "exefs");
+            if (version && bootable(candidate) && (!best_version || *version > *best_version)) {
+                best_version = version;
+                exefs = candidate;
+            }
+        }
+    }
+    const auto base = FindDirectory(root, "base");
+    if (exefs.empty()) {
+        exefs = FindDirectory(base, "exefs");
+    }
+    if (exefs.empty()) {
+        exefs = FindDirectory(root, "exefs");
+    }
+    if (!bootable(exefs)) {
+        return false;
+    }
+    return !FindDirectory(exefs.parent_path(), "romfs").empty() ||
+           !FindDirectory(base, "romfs").empty();
+}
+
+std::optional<u64> ParseTitleId(const std::string& name) {
+    u64 value{};
+    const auto* end = name.data() + name.size();
+    const auto [ptr, ec] = std::from_chars(name.data(), end, value, 16);
+    if (name.size() != 16 || ec != std::errc{} || ptr != end) {
+        return std::nullopt;
+    }
+    return value;
+}
+
+std::string ToHex(std::span<const u8> data) {
+    static constexpr char digits[] = "0123456789abcdef";
+    std::string out;
+    out.reserve(data.size() * 2);
+    for (const u8 byte : data) {
+        out += digits[byte >> 4];
+        out += digits[byte & 0xF];
+    }
+    return out;
+}
+
+std::vector<u8> FromHex(const std::string& hex) {
+    if (hex.size() % 2 != 0) {
+        throw PackError(PackResult::IoError, "malformed journal");
+    }
+    std::vector<u8> out(hex.size() / 2);
+    for (size_t i = 0; i < out.size(); ++i) {
+        const auto [ptr, ec] = std::from_chars(hex.data() + i * 2, hex.data() + i * 2 + 2, out[i], 16);
+        if (ec != std::errc{} || ptr != hex.data() + i * 2 + 2) {
+            throw PackError(PackResult::IoError, "malformed journal");
+        }
+    }
+    return out;
+}
+
+std::vector<u8> ReadWholeFile(const fs::path& path) {
+    Common::FS::IOFile in{path, Common::FS::FileAccessMode::Read};
+    if (!in.IsOpen()) {
+        return {};
+    }
+    std::vector<u8> data(in.GetSize());
+    if (in.ReadSpan(std::span{data}) != data.size()) {
+        return {};
+    }
+    return data;
+}
+
+// Same as pack.py: the program ID at ACI0 + 0x10, whatever the NPDM header revision.
+std::optional<u64> NpdmProgramId(std::span<const u8> npdm) {
+    static constexpr std::array<u8, 4> aci0{'A', 'C', 'I', '0'};
+    const auto it = std::search(npdm.begin(), npdm.end(), aci0.begin(), aci0.end());
+    const auto offset = static_cast<size_t>(it - npdm.begin());
+    if (it == npdm.end() || offset + 0x18 > npdm.size()) {
+        return std::nullopt;
+    }
+    u64 id = 0;
+    for (size_t i = 0; i < 8; ++i) {
+        id |= static_cast<u64>(npdm[offset + 0x10 + i]) << (8 * i);
+    }
+    return id;
+}
+
+void PutLE(std::vector<u8>& buffer, size_t offset, u64 value, size_t bytes) {
+    for (size_t i = 0; i < bytes; ++i) {
+        buffer[offset + i] = static_cast<u8>(value >> (8 * i));
+    }
+}
+
+void PutBytes(std::vector<u8>& buffer, size_t offset, std::span<const u8> bytes) {
+    std::memcpy(buffer.data() + offset, bytes.data(), bytes.size());
+}
+
+using Digest = std::array<u8, 32>;
+
+class Sha256 {
+public:
+    Sha256() : ctx{EVP_MD_CTX_new()} {
+        if (!ctx) {
+            throw PackError(PackResult::IoError, "cannot initialise SHA-256");
+        }
+        Reset();
+    }
+    ~Sha256() {
+        EVP_MD_CTX_free(ctx);
+    }
+    Sha256(const Sha256&) = delete;
+    Sha256& operator=(const Sha256&) = delete;
+
+    void Reset() {
+        if (EVP_DigestInit_ex(ctx, EVP_sha256(), nullptr) != 1) {
+            throw PackError(PackResult::IoError, "cannot initialise SHA-256");
+        }
+    }
+
+    void Update(const void* data, size_t size) {
+        EVP_DigestUpdate(ctx, data, size);
+    }
+
+    Digest Final() {
+        Digest digest{};
+        unsigned int length{};
+        EVP_DigestFinal_ex(ctx, digest.data(), &length);
+        return digest;
+    }
+
+private:
+    EVP_MD_CTX* ctx;
+};
+
+class ZstdContext {
+public:
+    // Archives must be byte-identical across platforms, so compression is always
+    // single-threaded (zstd's multithreaded frames differ) and every frame parameter is set
+    // explicitly instead of relying on library defaults.
+    explicit ZstdContext(int level) : cctx{ZSTD_createCCtx()} {
+        if (!cctx || ZSTD_isError(ZSTD_CCtx_setParameter(cctx, ZSTD_c_compressionLevel, level)) ||
+            ZSTD_isError(ZSTD_CCtx_setParameter(cctx, ZSTD_c_nbWorkers, 0)) ||
+            ZSTD_isError(ZSTD_CCtx_setParameter(cctx, ZSTD_c_contentSizeFlag, 1)) ||
+            ZSTD_isError(ZSTD_CCtx_setParameter(cctx, ZSTD_c_checksumFlag, 0)) ||
+            ZSTD_isError(ZSTD_CCtx_setParameter(cctx, ZSTD_c_dictIDFlag, 0))) {
+            throw PackError(PackResult::IoError, "cannot initialise zstd");
+        }
+    }
+    ~ZstdContext() {
+        ZSTD_freeCCtx(cctx);
+    }
+    ZstdContext(const ZstdContext&) = delete;
+    ZstdContext& operator=(const ZstdContext&) = delete;
+
+    // The pledged size makes zstd record the content size in the frame header, which the
+    // format requires.
+    void Begin(u64 size) {
+        if (ZSTD_isError(ZSTD_CCtx_reset(cctx, ZSTD_reset_session_only)) ||
+            ZSTD_isError(ZSTD_CCtx_setPledgedSrcSize(cctx, size))) {
+            throw PackError(PackResult::IoError, "cannot start zstd frame");
+        }
+    }
+
+    ZSTD_CCtx* get() const {
+        return cctx;
+    }
+
+private:
+    ZSTD_CCtx* cctx;
+};
+
+// One package and the metadata it is written with. The plan is everything that must survive a
+// low-storage run deleting its sources, so it is what the journal stores.
+struct PlanPackage {
+    u8 kind{};
+    u8 flags{};
+    u64 title_id{};
+    u32 version{};
+    std::vector<u8> meta;
+};
+
+struct PlanEntry {
+    u32 package{};
+    std::string path;   // inside the package tree, e.g. "romfs/Data/file.bin"
+    std::string source; // relative to the dump root
+    bool directory{};
+};
+
+struct Plan {
+    std::vector<PlanPackage> packages;
+    std::vector<PlanEntry> entries;
+};
+
+struct Extent {
+    u64 size{};
+    Digest sha256{};
+    u64 offset{};
+    u64 stored_size{};
+    u8 codec{};
+};
+
+struct Layout {
+    struct Dir {
+        std::string name;
+        u32 first_child{};
+        u32 child_count{};
+    };
+    struct File {
+        std::string name;
+        size_t entry{};
+    };
+    struct Package {
+        u32 root_dir{};
+        u32 exefs_dir = NoDir;
+        u32 romfs_dir = NoDir;
+    };
+    std::vector<Dir> dirs;
+    std::vector<File> files;
+    std::vector<u64> children; // FileTag | file index, or dir index
+    std::vector<Package> packages;
+    std::string pool;
+    std::unordered_map<std::string, u32> pool_index;
+    u64 toc_size{};
+    u64 blob_offset{};
+
+    static constexpr u64 FileTag = 1ULL << 32;
+
+    u32 Intern(const std::string& name) {
+        const auto [it, inserted] = pool_index.try_emplace(name, static_cast<u32>(pool.size()));
+        if (inserted) {
+            pool += name;
+        }
+        return it->second;
+    }
+};
+
+// Children sorted by the bytes of their names: std::string compares as unsigned char.
+struct TreeDir {
+    struct Child {
+        std::unique_ptr<TreeDir> dir;
+        size_t file_entry{};
+    };
+    std::string name;
+    std::map<std::string, Child> children;
+
+    TreeDir* Descend(const std::string& component) {
+        auto& child = children[component];
+        if (!child.dir) {
+            child.dir = std::make_unique<TreeDir>();
+            child.dir->name = component;
+        }
+        return child.dir.get();
+    }
+};
+
+// Lays out nodes as pack.py does: directories in pre-order, each directory's child slots
+// contiguous, its files numbered in slot order before its subdirectories are visited.
+u32 AssignDir(TreeDir& dir, Layout& layout) {
+    const auto id = static_cast<u32>(layout.dirs.size());
+    layout.dirs.push_back({dir.name, static_cast<u32>(layout.children.size()),
+                           static_cast<u32>(dir.children.size())});
+    const size_t slot_base = layout.children.size();
+    layout.children.resize(slot_base + dir.children.size());
+    size_t slot = slot_base;
+    for (auto& [name, child] : dir.children) {
+        if (!child.dir) {
+            layout.children[slot] = Layout::FileTag | layout.files.size();
+            layout.files.push_back({name, child.file_entry});
+        }
+        ++slot;
+    }
+    slot = slot_base;
+    for (auto& [name, child] : dir.children) {
+        if (child.dir) {
+            layout.children[slot] = AssignDir(*child.dir, layout);
+        }
+        ++slot;
+    }
+    return id;
+}
+
+Layout BuildLayout(const Plan& plan) {
+    std::vector<TreeDir> roots(plan.packages.size());
+    for (size_t i = 0; i < plan.entries.size(); ++i) {
+        const auto& entry = plan.entries[i];
+        TreeDir* dir = &roots.at(entry.package);
+        size_t start = 0;
+        while (true) {
+            const auto slash = entry.path.find('/', start);
+            const auto component = entry.path.substr(start, slash - start);
+            if (slash == std::string::npos) {
+                if (entry.directory) {
+                    dir->Descend(component);
+                } else {
+                    auto& child = dir->children[component];
+                    if (child.dir) {
+                        throw PackError(PackResult::InvalidSource,
+                                        "a file and a folder share the name " + entry.path);
+                    }
+                    child.file_entry = i;
+                }
+                break;
+            }
+            dir = dir->Descend(component);
+            start = slash + 1;
+        }
+    }
+
+    Layout layout;
+    for (auto& root : roots) {
+        Layout::Package package;
+        package.root_dir = AssignDir(root, layout);
+        const auto& root_dir = layout.dirs[package.root_dir];
+        for (u32 slot = root_dir.first_child; slot < root_dir.first_child + root_dir.child_count;
+             ++slot) {
+            const u64 child = layout.children[slot];
+            if (child & Layout::FileTag) {
+                continue;
+            }
+            const auto id = static_cast<u32>(child);
+            if (layout.dirs[id].name == "exefs") {
+                package.exefs_dir = id;
+            } else if (layout.dirs[id].name == "romfs") {
+                package.romfs_dir = id;
+            }
+        }
+        layout.packages.push_back(package);
+    }
+
+    if (layout.dirs.size() + layout.files.size() >= NoDir) {
+        throw PackError(PackResult::InvalidSource, "the dump has too many files");
+    }
+    for (const auto& dir : layout.dirs) {
+        layout.Intern(dir.name);
+    }
+    for (const auto& file : layout.files) {
+        layout.Intern(file.name);
+    }
+    if (layout.pool.size() > std::numeric_limits<u32>::max()) {
+        throw PackError(PackResult::InvalidSource, "the dump's file names are too long");
+    }
+
+    const u64 unpadded = TocHeaderSize + plan.packages.size() * PackageRecordSize +
+                         layout.dirs.size() * DirRecordSize + layout.files.size() * FileRecordSize +
+                         layout.children.size() * sizeof(u32) + layout.pool.size();
+    layout.toc_size = AlignUp(unpadded, ExtentAlignment);
+    layout.blob_offset = AlignUp(SuperblockSize + layout.toc_size, ExtentAlignment);
+    return layout;
+}
+
+std::vector<u8> SerializeTlvs(std::vector<std::pair<u16, std::vector<u8>>> records) {
+    std::ranges::stable_sort(records, {}, &std::pair<u16, std::vector<u8>>::first);
+    std::vector<u8> out;
+    for (const auto& [type, payload] : records) {
+        const size_t at = out.size();
+        out.resize(at + 8 + payload.size());
+        PutLE(out, at, type, 2);
+        PutLE(out, at + 4, payload.size(), 4);
+        PutBytes(out, at + 8, payload);
+    }
+    return out;
+}
+
+std::vector<u8> StringBytes(const std::string& value) {
+    return {value.begin(), value.end()};
+}
+
+// The dump's own loader supplies control data and the display version, the same way a loose
+// dump reports them when it boots (control.nacp beside it, else the RomFS's version tag).
+std::unique_ptr<Loader::AppLoader_DeconstructedRomDirectory> OpenLoader(
+    RealVfsFilesystem& vfs, const fs::path& package_dir) {
+    const auto exefs = FindDirectory(package_dir, "exefs");
+    if (exefs.empty() || !IsFile(exefs / "main")) {
+        return nullptr;
+    }
+    auto main = vfs.OpenFile(Common::FS::PathToUTF8String(exefs / "main"), OpenMode::Read);
+    if (!main) {
+        return nullptr;
+    }
+    return std::make_unique<Loader::AppLoader_DeconstructedRomDirectory>(std::move(main));
+}
+
+class Discovery {
+public:
+    Discovery(const fs::path& dump_root_, std::vector<fs::path> excluded_)
+        : dump_root{dump_root_}, excluded{std::move(excluded_)} {}
+
+    Plan Run() {
+        const auto base = FindDirectory(dump_root, "base");
+        const auto updates = FindDirectory(dump_root, "updates");
+        const auto dlc = FindDirectory(dump_root, "dlc");
+
+        std::optional<u64> base_title_id;
+        if (!base.empty() && HasContent(base)) {
+            base_title_id = AddPackage(KindBase, base, 0, {});
+        } else if (updates.empty() && HasContent(dump_root)) {
+            base_title_id = AddPackage(KindBase, dump_root, 0, {"base", "updates", "dlc"});
+        }
+
+        std::vector<std::pair<u64, fs::path>> versions;
+        std::error_code ec;
+        if (!updates.empty()) {
+            for (const auto& entry : fs::directory_iterator(updates, ec)) {
+                const auto version = ParseDecimal(ToUtf8(entry.path().filename()));
+                if (version && entry.is_directory(ec) && HasContent(entry.path())) {
+                    if (*version > std::numeric_limits<u32>::max()) {
+                        throw PackError(PackResult::InvalidSource,
+                                        "update version out of range: " + ToUtf8(entry.path()));
+                    }
+                    versions.emplace_back(*version, entry.path());
+                }
+            }
+        }
+        std::ranges::sort(versions);
+        const u8 update_flags = base_title_id ? 0 : FlagStandaloneUpdate;
+        for (const auto& [version, path] : versions) {
+            AddPackage(KindUpdate, path, static_cast<u32>(version), {}, update_flags,
+                       base_title_id.value_or(0));
+        }
+
+        if (!dlc.empty()) {
+            std::vector<std::pair<std::string, fs::path>> addons;
+            for (const auto& title : fs::directory_iterator(dlc, ec)) {
+                const auto title_name = ToUtf8(title.path().filename());
+                if (!ParseTitleId(title_name) || !title.is_directory(ec)) {
+                    continue;
+                }
+                for (const auto& content : fs::directory_iterator(title.path(), ec)) {
+                    if (content.is_directory(ec) && HasContent(content.path())) {
+                        addons.emplace_back(title_name + "/" + ToUtf8(content.path().filename()),
+                                            content.path());
+                    }
+                }
+            }
+            std::ranges::sort(addons);
+            for (const auto& [name, path] : addons) {
+                AddPackage(KindAddon, path, 0, {}, 0, *ParseTitleId(name.substr(0, 16)));
+            }
+        }
+
+        if (plan.packages.empty()) {
+            throw PackError(PackResult::InvalidSource, "no packages found in the dump");
+        }
+        AddApplicationMetadata();
+        for (size_t i = 0; i < plan.packages.size(); ++i) {
+            auto& tlvs = package_tlvs[i];
+            tlvs.emplace_back(TlvSourceDump, StringBytes(ToUtf8(dump_root.filename())));
+            plan.packages[i].meta = SerializeTlvs(std::move(tlvs));
+        }
+        return std::move(plan);
+    }
+
+private:
+    static bool HasContent(const fs::path& dir) {
+        return !FindDirectory(dir, "exefs").empty() || !FindDirectory(dir, "romfs").empty();
+    }
+
+    // Returns the package's title ID: the NPDM program ID, else the folder's or base's.
+    u64 AddPackage(u8 kind, const fs::path& dir, u32 version,
+                   const std::vector<std::string>& skip, u8 flags = 0, u64 fallback_id = 0) {
+        const auto index = static_cast<u32>(plan.packages.size());
+        PlanPackage package{kind, flags, fallback_id, version, {}};
+        auto& tlvs = package_tlvs.emplace_back();
+
+        const auto exefs = FindDirectory(dir, "exefs");
+        const auto romfs = FindDirectory(dir, "romfs");
+        fs::path npdm_path = exefs.empty() ? fs::path{} : exefs / "main.npdm";
+        if (!IsFile(npdm_path)) {
+            npdm_path = dir / "main.npdm";
+        }
+        if (IsFile(npdm_path)) {
+            auto npdm = ReadWholeFile(npdm_path);
+            if (const auto id = NpdmProgramId(npdm); kind != KindAddon && id && *id != 0) {
+                package.title_id = *id;
+            }
+            tlvs.emplace_back(TlvNpdm, std::move(npdm));
+        }
+
+        if (kind != KindAddon) {
+            if (auto loader = OpenLoader(vfs, dir)) {
+                std::string display_version;
+                if (loader->ReadDisplayVersion(display_version) == Loader::ResultStatus::Success &&
+                    !display_version.empty()) {
+                    tlvs.emplace_back(TlvDisplayVersion, StringBytes(display_version));
+                }
+                loaders.emplace_back(index, std::move(loader));
+            }
+        }
+        plan.packages.push_back(std::move(package));
+
+        if (!exefs.empty()) {
+            CollectTree(index, exefs, "exefs");
+        }
+        if (!romfs.empty()) {
+            CollectTree(index, romfs, "romfs");
+        }
+        std::error_code ec;
+        for (const auto& entry : fs::directory_iterator(dir, ec)) {
+            const auto name = ToUtf8(entry.path().filename());
+            const auto lower = Lower(name);
+            if (entry.path() == exefs || entry.path() == romfs ||
+                std::ranges::find(skip, lower) != skip.end()) {
+                continue;
+            }
+            if (entry.is_directory(ec)) {
+                CollectTree(index, entry.path(), "data/" + name);
+            } else {
+                AddFile(index, entry, "data/" + name);
+            }
+        }
+        return plan.packages.back().title_id;
+    }
+
+    // Names, icon and control data belong to the base package, or the first one without a base.
+    // Our dumps rarely carry a control folder; when one does, the base's own wins, then updates.
+    void AddApplicationMetadata() {
+        const auto app = static_cast<u32>(std::distance(
+            plan.packages.begin(), std::ranges::find(plan.packages, KindBase, &PlanPackage::kind)));
+        const u32 target = app < plan.packages.size() ? app : 0;
+        std::ranges::stable_sort(loaders, [target](const auto& a, const auto& b) {
+            return (a.first == target) > (b.first == target);
+        });
+
+        auto& tlvs = package_tlvs[target];
+        bool have_control = false;
+        bool have_icon = false;
+        for (const auto& [index, loader] : loaders) {
+            NACP control;
+            if (!have_control &&
+                loader->ReadControlData(control) == Loader::ResultStatus::Success) {
+                have_control = true;
+                tlvs.emplace_back(TlvNacp, control.GetRawBytes());
+                if (const auto name = control.GetApplicationName(); !name.empty()) {
+                    tlvs.emplace_back(TlvTitleName, StringBytes(name));
+                }
+                if (const auto publisher = control.GetDeveloperName(); !publisher.empty()) {
+                    tlvs.emplace_back(TlvPublisher, StringBytes(publisher));
+                }
+            }
+            std::vector<u8> icon;
+            if (!have_icon && loader->ReadIcon(icon) == Loader::ResultStatus::Success &&
+                !icon.empty()) {
+                have_icon = true;
+                tlvs.emplace_back(TlvIcon, std::move(icon));
+            }
+        }
+    }
+
+    bool IsExcluded(const fs::path& path) const {
+        const auto normal = fs::absolute(path).lexically_normal();
+        return std::ranges::find(excluded, normal) != excluded.end();
+    }
+
+    void AddFile(u32 package, const fs::directory_entry& entry, const std::string& path) {
+        std::error_code ec;
+        if (entry.is_symlink(ec)) {
+            throw PackError(PackResult::InvalidSource,
+                            "symlinks are not supported: " + ToUtf8(entry.path()));
+        }
+        if (!entry.is_regular_file(ec)) {
+            throw PackError(PackResult::InvalidSource,
+                            "unsupported file type: " + ToUtf8(entry.path()));
+        }
+        // Dump-tool listings are excluded by the spec.
+        if (entry.path().filename() == ".listing" || IsExcluded(entry.path())) {
+            return;
+        }
+        plan.entries.push_back({package, path, Relative(entry.path()), false});
+    }
+
+    void CollectTree(u32 package, const fs::path& root, const std::string& prefix) {
+        plan.entries.push_back({package, prefix, Relative(root), true});
+        for (auto it = fs::recursive_directory_iterator(root);
+             it != fs::recursive_directory_iterator(); ++it) {
+            const auto& entry = *it;
+            const auto path = prefix + "/" + ToUtf8(fs::relative(entry.path(), root));
+            if (!entry.is_symlink() && entry.is_directory()) {
+                plan.entries.push_back({package, path, Relative(entry.path()), true});
+            } else {
+                AddFile(package, entry, path);
+            }
+        }
+    }
+
+    std::string Relative(const fs::path& path) const {
+        return ToUtf8(fs::relative(path, dump_root));
+    }
+
+    fs::path dump_root;
+    std::vector<fs::path> excluded;
+    RealVfsFilesystem vfs;
+    Plan plan;
+    std::vector<std::vector<std::pair<u16, std::vector<u8>>>> package_tlvs;
+    std::vector<std::pair<u32, std::unique_ptr<Loader::AppLoader_DeconstructedRomDirectory>>>
+        loaders;
+};
+
+Json PlanToJson(const Plan& plan) {
+    Json packages = Json::array();
+    for (const auto& package : plan.packages) {
+        packages.push_back(Json{{"kind", package.kind},
+                                {"flags", package.flags},
+                                {"title_id", package.title_id},
+                                {"version", package.version},
+                                {"meta", ToHex(package.meta)}});
+    }
+    Json entries = Json::array();
+    for (const auto& entry : plan.entries) {
+        entries.push_back(Json{{"package", entry.package},
+                               {"path", entry.path},
+                               {"source", entry.source},
+                               {"directory", entry.directory}});
+    }
+    return Json{{"format", "nup-journal"},
+                {"version", JournalVersion},
+                {"packages", packages},
+                {"entries", entries}};
+}
+
+Plan PlanFromJson(const Json& json) {
+    if (json.at("format") != "nup-journal" || json.at("version") != JournalVersion) {
+        throw PackError(PackResult::IoError, "unsupported journal");
+    }
+    Plan plan;
+    for (const auto& package : json.at("packages")) {
+        plan.packages.push_back({package.at("kind").get<u8>(), package.at("flags").get<u8>(),
+                                 package.at("title_id").get<u64>(),
+                                 package.at("version").get<u32>(),
+                                 FromHex(package.at("meta").get<std::string>())});
+    }
+    for (const auto& entry : json.at("entries")) {
+        plan.entries.push_back({entry.at("package").get<u32>(), entry.at("path").get<std::string>(),
+                                entry.at("source").get<std::string>(),
+                                entry.at("directory").get<bool>()});
+    }
+    return plan;
+}
+
+void RemoveFile(const fs::path& path) {
+    std::error_code ec;
+    fs::remove(path, ec);
+}
+
+bool IsEmptyDirectory(const fs::path& path) {
+    std::error_code ec;
+    return fs::is_directory(path, ec) && fs::is_empty(path, ec) && !ec;
+}
+
+void RemoveEmptyTree(const fs::path& root) {
+    std::error_code ec;
+    std::vector<fs::path> directories;
+    for (auto it = fs::recursive_directory_iterator(root, ec);
+         !ec && it != fs::recursive_directory_iterator(); it.increment(ec)) {
+        if (it->is_directory(ec)) {
+            directories.push_back(it->path());
+        }
+    }
+    for (auto it = directories.rbegin(); it != directories.rend(); ++it) {
+        if (IsEmptyDirectory(*it)) {
+            fs::remove(*it, ec);
+        }
+    }
+    if (IsEmptyDirectory(root)) {
+        fs::remove(root, ec);
+    }
+}
+
+void RemoveEmptyParents(fs::path path, const fs::path& dump_root) {
+    while (!path.empty() && path.has_relative_path()) {
+        std::error_code ec;
+        if (fs::equivalent(path, dump_root, ec) || ec || !IsEmptyDirectory(path)) {
+            break;
+        }
+        fs::remove(path, ec);
+        path = path.parent_path();
+    }
+}
+
+class Packer {
+public:
+    Packer(const fs::path& dump_root_, const fs::path& archive_, const PackOptions& options_,
+           const std::function<void(const PackProgress&)>& progress_,
+           const std::atomic_bool* cancel_)
+        : dump_root{dump_root_}, archive{archive_}, part{WithSuffix(archive_, ".part")},
+          journal{WithSuffix(archive_, ".journal")}, options{options_}, progress_cb{progress_},
+          cancel{cancel_} {}
+
+    PackResult Run() {
+        std::error_code ec;
+        if (fs::exists(archive, ec)) {
+            throw PackError(PackResult::IoError, "archive already exists: " + ToUtf8(archive));
+        }
+        // A journal without a complete plan line was cut short before anything was deleted.
+        const bool resume =
+            options.delete_sources && HasResumableJournal(archive) && LoadJournal();
+        if (resume) {
+            OpenForResume();
+        } else {
+            if (!IsLooseDump(dump_root)) {
+                throw PackError(PackResult::InvalidSource,
+                                "expected exefs/main, exefs/main.npdm and a romfs folder");
+            }
+            std::vector<fs::path> excluded;
+            for (const auto& path : {archive, part, journal}) {
+                excluded.push_back(fs::absolute(path).lexically_normal());
+            }
+            plan = Discovery{dump_root, std::move(excluded)}.Run();
+            layout = BuildLayout(plan);
+            OpenNew();
+        }
+        extents.resize(layout.files.size());
+        done.resize(layout.files.size());
+        for (const auto& [index, extent] : journaled) {
+            extents[index] = extent;
+            done[index] = true;
+            Remember(extent);
+        }
+        CountTotals();
+        Report();
+
+        for (size_t i = 0; i < layout.files.size(); ++i) {
+            if (done[i]) {
+                continue;
+            }
+            PackFile(i);
+            if (options.delete_sources &&
+                (chunk_bytes >= options.chunk_bytes || chunk.size() >= MaxChunkFiles)) {
+                Checkpoint();
+            }
+        }
+        if (options.delete_sources) {
+            Checkpoint();
+        }
+
+        Finish();
+        out.Close();
+        fs::rename(part, archive, ec);
+        if (ec) {
+            throw PackError(PackResult::IoError, "cannot rename archive: " + ec.message());
+        }
+
+        if (options.delete_sources) {
+            RemoveFile(journal);
+            RemoveSourceFolders();
+        }
+        return PackResult::Success;
+    }
+
+    void Abort() {
+        out.Close();
+        if (!options.delete_sources) {
+            RemoveFile(part);
+        }
+    }
+
+private:
+    void OpenNew() {
+        RemoveFile(journal);
+        out.Open(part, Common::FS::FileAccessMode::Write);
+        if (!out.IsOpen()) {
+            throw PackError(PackResult::IoError, "cannot create " + ToUtf8(part));
+        }
+        WriteZeros(layout.blob_offset);
+        cursor = layout.blob_offset;
+        if (options.delete_sources) {
+            AppendJournal(PlanToJson(plan).dump() + '\n');
+        }
+    }
+
+    bool LoadJournal() {
+        const auto contents =
+            Common::FS::ReadStringFromFile(journal, Common::FS::FileType::BinaryFile);
+        size_t start = 0;
+        bool have_plan = false;
+        while (start < contents.size()) {
+            const auto line_end = contents.find('\n', start);
+            if (line_end == std::string::npos) {
+                break;
+            }
+            const auto line = std::string_view{contents}.substr(start, line_end - start);
+            start = line_end + 1;
+            Json json;
+            try {
+                json = Json::parse(line);
+            } catch (const Json::exception&) {
+                // Only the tail can be torn: the journal is synced before sources are deleted.
+                break;
+            }
+            if (!have_plan) {
+                plan = PlanFromJson(json);
+                layout = BuildLayout(plan);
+                resume_end = layout.blob_offset;
+                have_plan = true;
+                continue;
+            }
+            const auto index = json.at("file").get<size_t>();
+            const auto sha = FromHex(json.at("sha256").get<std::string>());
+            if (index >= layout.files.size() || sha.size() != 32) {
+                throw PackError(PackResult::IoError, "malformed journal");
+            }
+            Extent extent{json.at("size").get<u64>(), {}, json.at("offset").get<u64>(),
+                          json.at("stored_size").get<u64>(), json.at("codec").get<u8>()};
+            std::ranges::copy(sha, extent.sha256.begin());
+            resume_end = std::max(resume_end, extent.offset + extent.stored_size);
+            journaled.emplace_back(index, extent);
+        }
+        return have_plan;
+    }
+
+    void OpenForResume() {
+        const u64 end = resume_end;
+        out.Open(part, Common::FS::FileAccessMode::ReadWrite);
+        if (!out.IsOpen()) {
+            throw PackError(PackResult::IoError, "cannot open " + ToUtf8(part));
+        }
+        if (out.GetSize() < end) {
+            throw PackError(PackResult::IoError, "partial archive is shorter than its journal; "
+                                                 "delete " +
+                                                     ToUtf8(part) + " and " + ToUtf8(journal) +
+                                                     " to start over");
+        }
+        if (!out.SetSize(end) || !out.Seek(static_cast<s64>(end))) {
+            throw PackError(PackResult::IoError, "cannot truncate " + ToUtf8(part));
+        }
+        cursor = end;
+
+        // Journaled before an interruption, but the delete never happened.
+        for (const auto& [index, extent] : journaled) {
+            RemoveFile(SourceOf(index));
+        }
+    }
+
+    fs::path SourceOf(size_t file_index) const {
+        return dump_root / FromUtf8(plan.entries[layout.files[file_index].entry].source);
+    }
+
+    void CountTotals() {
+        for (size_t i = 0; i < layout.files.size(); ++i) {
+            ++progress.files_total;
+            if (done[i]) {
+                progress.bytes_total += extents[i].size;
+                progress.bytes_done += extents[i].size;
+                ++progress.files_done;
+            } else {
+                std::error_code ec;
+                const auto size = fs::file_size(SourceOf(i), ec);
+                if (ec) {
+                    throw PackError(PackResult::InvalidSource,
+                                    "missing source file: " + ToUtf8(SourceOf(i)));
+                }
+                progress.bytes_total += size;
+            }
+        }
+    }
+
+    void Remember(const Extent& extent) {
+        if (extent.size == 0) {
+            return;
+        }
+        sizes_seen.insert(extent.size);
+        by_hash.try_emplace(extent.sha256, extent);
+    }
+
+    bool Cancelled() const {
+        return cancel && cancel->load();
+    }
+
+    void WriteZeros(u64 count) {
+        static constexpr std::array<u8, 4096> zeros{};
+        while (count > 0) {
+            const auto n = static_cast<size_t>(std::min<u64>(count, zeros.size()));
+            Write(zeros.data(), n);
+            count -= n;
+        }
+    }
+
+    void Write(const u8* data, size_t size) {
+        if (out.WriteSpan(std::span<const u8>{data, size}) != size) {
+            throw PackError(PackResult::IoError, "write failed, the disk may be full");
+        }
+    }
+
+    void AddProgress(u64 bytes) {
+        progress.bytes_done += bytes;
+        if (progress.bytes_done - last_report >= ProgressStep) {
+            Report();
+        }
+    }
+
+    // Reads the whole source through `sink`, checking that it still has the expected size. A file
+    // read more than once (hashed for dedup, or compressed and then stored raw) counts once.
+    template <typename Sink>
+    void ReadSource(Common::FS::IOFile& in, u64 size, Sink&& sink) {
+        if (!in.Seek(0)) {
+            throw PackError(PackResult::IoError, "cannot seek source");
+        }
+        buffer.resize(ReadBufferSize);
+        u64 total = 0;
+        while (true) {
+            if (Cancelled()) {
+                throw PackError(PackResult::Cancelled, "cancelled");
+            }
+            const auto read = in.ReadSpan(std::span{buffer});
+            if (read == 0) {
+                break;
+            }
+            total += read;
+            if (total > size) {
+                break;
+            }
+            if (total > file_counted) {
+                AddProgress(total - file_counted);
+                file_counted = total;
+            }
+            if (!sink(buffer.data(), read)) {
+                return;
+            }
+        }
+        if (total != size) {
+            throw PackError(PackResult::IoError, "a source file changed while packing");
+        }
+    }
+
+    Digest HashSource(Common::FS::IOFile& in, u64 size) {
+        hash.Reset();
+        ReadSource(in, size, [this](const u8* data, size_t n) {
+            hash.Update(data, n);
+            return true;
+        });
+        return hash.Final();
+    }
+
+    ZstdContext& Compressor() {
+        if (!compressor) {
+            compressor = std::make_unique<ZstdContext>(options.zstd_level);
+        }
+        return *compressor;
+    }
+
+    // Streams one zstd frame into the archive. Gives up (returns false) as soon as the output is
+    // no smaller than the input.
+    bool WriteCompressed(Common::FS::IOFile& in, u64 size, u64& stored) {
+        auto& zstd = Compressor();
+        zstd.Begin(size);
+        out_buffer.resize(ZSTD_CStreamOutSize());
+        stored = 0;
+        bool fits = true;
+        const auto drain = [&](ZSTD_inBuffer& input, ZSTD_EndDirective mode) {
+            while (true) {
+                ZSTD_outBuffer output{out_buffer.data(), out_buffer.size(), 0};
+                const size_t remaining = ZSTD_compressStream2(zstd.get(), &output, &input, mode);
+                if (ZSTD_isError(remaining)) {
+                    throw PackError(PackResult::IoError,
+                                    std::string{"zstd: "} + ZSTD_getErrorName(remaining));
+                }
+                stored += output.pos;
+                if (stored >= size) {
+                    return false;
+                }
+                Write(out_buffer.data(), output.pos);
+                const bool finished = mode == ZSTD_e_end ? remaining == 0
+                                                         : input.pos == input.size;
+                if (finished) {
+                    return true;
+                }
+            }
+        };
+        hash.Reset();
+        ReadSource(in, size, [&](const u8* data, size_t n) {
+            hash.Update(data, n);
+            ZSTD_inBuffer input{data, n, 0};
+            fits = drain(input, ZSTD_e_continue);
+            return fits;
+        });
+        if (!fits) {
+            return false;
+        }
+        ZSTD_inBuffer empty{nullptr, 0, 0};
+        return drain(empty, ZSTD_e_end);
+    }
+
+    void PackFile(size_t index) {
+        const auto source = SourceOf(index);
+        Common::FS::IOFile in{source, Common::FS::FileAccessMode::Read};
+        if (!in.IsOpen()) {
+            throw PackError(PackResult::IoError, "cannot read " + ToUtf8(source));
+        }
+        Extent extent;
+        extent.size = in.GetSize();
+        file_counted = 0;
+
+        std::optional<Digest> known_hash;
+        if (extent.size == 0) {
+            known_hash = HashSource(in, 0);
+        } else if (sizes_seen.contains(extent.size)) {
+            // Only a file whose size matches an earlier extent can be a duplicate; hash it before
+            // writing anything so the shared extent costs no output.
+            known_hash = HashSource(in, extent.size);
+            if (const auto it = by_hash.find(*known_hash);
+                it != by_hash.end() && it->second.size == extent.size) {
+                extent = it->second;
+                Complete(index, extent);
+                return;
+            }
+        }
+
+        if (extent.size == 0) {
+            extent.sha256 = *known_hash;
+            Complete(index, extent);
+            return;
+        }
+
+        const u64 start = AlignUp(cursor, ExtentAlignment);
+        Seek(cursor);
+        WriteZeros(start - cursor);
+        extent.offset = start;
+
+        bool compressed = false;
+        if (extent.size <= options.raw_threshold && options.zstd_level > 0) {
+            u64 stored = 0;
+            compressed = WriteCompressed(in, extent.size, stored);
+            if (compressed) {
+                extent.codec = CodecZstd;
+                extent.stored_size = stored;
+                extent.sha256 = hash.Final();
+            }
+        }
+        if (!compressed) {
+            Seek(start);
+            hash.Reset();
+            ReadSource(in, extent.size, [this](const u8* data, size_t n) {
+                hash.Update(data, n);
+                Write(data, n);
+                return true;
+            });
+            extent.codec = CodecRaw;
+            extent.stored_size = extent.size;
+            extent.sha256 = hash.Final();
+        }
+        cursor = start + extent.stored_size;
+        Remember(extent);
+        Complete(index, extent);
+    }
+
+    void Seek(u64 offset) {
+        if (!out.Seek(static_cast<s64>(offset))) {
+            throw PackError(PackResult::IoError, "cannot seek " + ToUtf8(part));
+        }
+    }
+
+    void Complete(size_t index, const Extent& extent) {
+        extents[index] = extent;
+        done[index] = true;
+        if (options.delete_sources) {
+            chunk.push_back(index);
+            chunk_bytes += extent.size;
+        }
+        ++progress.files_done;
+        Report();
+    }
+
+    void AppendJournal(const std::string& lines) {
+        Common::FS::IOFile log{journal, Common::FS::FileAccessMode::Append};
+        if (!log.IsOpen() || log.WriteString(lines) != lines.size() || !log.Commit()) {
+            throw PackError(PackResult::IoError, "cannot write " + ToUtf8(journal));
+        }
+    }
+
+    // Archive data first, then the journal, then the deletes, so an interruption loses nothing.
+    void Checkpoint() {
+        if (chunk.empty()) {
+            return;
+        }
+        if (!out.Commit()) {
+            throw PackError(PackResult::IoError, "cannot sync " + ToUtf8(part));
+        }
+        std::string lines;
+        for (const auto index : chunk) {
+            const auto& extent = extents[index];
+            lines += Json{{"file", index},
+                          {"size", extent.size},
+                          {"sha256", ToHex(extent.sha256)},
+                          {"offset", extent.offset},
+                          {"stored_size", extent.stored_size},
+                          {"codec", extent.codec}}
+                         .dump();
+            lines += '\n';
+        }
+        AppendJournal(lines);
+        for (const auto index : chunk) {
+            RemoveFile(SourceOf(index));
+        }
+        chunk.clear();
+        chunk_bytes = 0;
+    }
+
+    void Finish() {
+        // Meta blocks follow the last extent, as pack.py writes them.
+        Seek(cursor);
+        std::vector<std::pair<u64, u32>> meta;
+        for (const auto& package : plan.packages) {
+            if (package.meta.size() > std::numeric_limits<u32>::max()) {
+                throw PackError(PackResult::IoError, "package metadata is too large");
+            }
+            meta.emplace_back(package.meta.empty() ? 0 : cursor,
+                              static_cast<u32>(package.meta.size()));
+            Write(package.meta.data(), package.meta.size());
+            cursor += package.meta.size();
+        }
+        const u64 file_size = cursor;
+
+        const auto toc = BuildToc(meta);
+        std::array<u8, 32> toc_hash{};
+        unsigned int hash_length{};
+        EVP_Digest(toc.data(), toc.size(), toc_hash.data(), &hash_length, EVP_sha256(), nullptr);
+
+        // UUID: SHA-256 over title_id (u64), version (u32) and kind (u8) of each package.
+        Sha256 uuid_hash;
+        for (const auto& package : plan.packages) {
+            std::vector<u8> identity(13);
+            PutLE(identity, 0, package.title_id, 8);
+            PutLE(identity, 8, package.version, 4);
+            identity[12] = package.kind;
+            uuid_hash.Update(identity.data(), identity.size());
+        }
+        const auto uuid = uuid_hash.Final();
+
+        std::vector<u8> super(SuperblockSize);
+        PutBytes(super, 0x00, Magic);
+        PutLE(super, 0x04, SuperblockSize, 2);
+        PutLE(super, 0x06, 1, 2);
+        PutLE(super, 0x08, SuperblockSize, 8);
+        PutLE(super, 0x10, toc.size(), 8);
+        PutBytes(super, 0x18, toc_hash);
+        PutLE(super, 0x38, layout.blob_offset, 8);
+        PutLE(super, 0x40, file_size, 8);
+        PutLE(super, 0x48, plan.packages.size(), 4);
+        PutBytes(super, 0x50, std::span{uuid}.first(16));
+
+        Seek(0);
+        Write(super.data(), super.size());
+        Write(toc.data(), toc.size());
+        if (!out.SetSize(file_size) || !out.Commit()) {
+            throw PackError(PackResult::IoError, "cannot finish " + ToUtf8(part));
+        }
+    }
+
+    // Every field is written little-endian at its documented offset. The package record is
+    // 0x40 bytes with 20 reserved bytes at 0x2C, as NupContainer reads it.
+    std::vector<u8> BuildToc(const std::vector<std::pair<u64, u32>>& meta) const {
+        std::vector<u8> toc(layout.toc_size);
+        const u64 dir_count = layout.dirs.size();
+        PutBytes(toc, 0x00, TocMagic);
+        PutLE(toc, 0x04, plan.packages.size(), 4);
+        PutLE(toc, 0x08, dir_count, 8);
+        PutLE(toc, 0x10, layout.files.size(), 8);
+
+        size_t pos = TocHeaderSize;
+        for (size_t i = 0; i < plan.packages.size(); ++i) {
+            const auto& package = plan.packages[i];
+            const auto& record = layout.packages[i];
+            PutLE(toc, pos + 0x00, package.title_id, 8);
+            PutLE(toc, pos + 0x08, record.root_dir, 4);
+            PutLE(toc, pos + 0x0C, record.exefs_dir, 4);
+            PutLE(toc, pos + 0x10, record.romfs_dir, 4);
+            PutLE(toc, pos + 0x14, package.version, 4);
+            toc[pos + 0x18] = package.kind;
+            toc[pos + 0x19] = package.flags;
+            PutLE(toc, pos + 0x20, meta[i].first, 8);
+            PutLE(toc, pos + 0x28, meta[i].second, 4);
+            pos += PackageRecordSize;
+        }
+        for (const auto& dir : layout.dirs) {
+            PutLE(toc, pos + 0x00, layout.pool_index.at(dir.name), 4);
+            PutLE(toc, pos + 0x04, dir.name.size(), 4);
+            PutLE(toc, pos + 0x08, dir.first_child, 4);
+            PutLE(toc, pos + 0x0C, dir.child_count, 4);
+            pos += DirRecordSize;
+        }
+        for (size_t i = 0; i < layout.files.size(); ++i) {
+            const auto& file = layout.files[i];
+            const auto& extent = extents[i];
+            PutLE(toc, pos + 0x00, layout.pool_index.at(file.name), 4);
+            PutLE(toc, pos + 0x04, file.name.size(), 4);
+            PutLE(toc, pos + 0x08, extent.size, 8);
+            // Empty files have no extent: offset, size and codec are all zero.
+            if (extent.size != 0) {
+                PutLE(toc, pos + 0x10, extent.offset, 8);
+                PutLE(toc, pos + 0x18, extent.stored_size, 8);
+                toc[pos + 0x40] = extent.codec;
+            }
+            PutBytes(toc, pos + 0x20, extent.sha256);
+            pos += FileRecordSize;
+        }
+        for (const u64 child : layout.children) {
+            const u64 id = (child & Layout::FileTag) ? dir_count + static_cast<u32>(child) : child;
+            PutLE(toc, pos, id, 4);
+            pos += sizeof(u32);
+        }
+        PutLE(toc, 0x18, pos, 8);
+        PutLE(toc, 0x20, layout.pool.size(), 8);
+        std::memcpy(toc.data() + pos, layout.pool.data(), layout.pool.size());
+        return toc;
+    }
+
+    void RemoveSourceFolders() {
+        for (const auto& entry : plan.entries) {
+            const auto depth = std::ranges::count(entry.path, '/');
+            const bool top = entry.directory &&
+                             (depth == 0 || (depth == 1 && entry.path.starts_with("data/")));
+            if (top) {
+                const auto source = dump_root / FromUtf8(entry.source);
+                RemoveEmptyTree(source);
+                RemoveEmptyParents(source.parent_path(), dump_root);
+            }
+        }
+    }
+
+    void Report() {
+        last_report = progress.bytes_done;
+        if (progress_cb) {
+            progress_cb(progress);
+        }
+    }
+
+    fs::path dump_root;
+    fs::path archive;
+    fs::path part;
+    fs::path journal;
+    PackOptions options;
+    std::function<void(const PackProgress&)> progress_cb;
+    const std::atomic_bool* cancel;
+
+    Plan plan;
+    Layout layout;
+    std::vector<Extent> extents;
+    std::vector<bool> done;
+    std::vector<std::pair<size_t, Extent>> journaled;
+
+    struct DigestHash {
+        size_t operator()(const Digest& digest) const {
+            size_t value;
+            std::memcpy(&value, digest.data(), sizeof(value));
+            return value;
+        }
+    };
+    std::unordered_map<Digest, Extent, DigestHash> by_hash;
+    std::unordered_set<u64> sizes_seen;
+
+    Common::FS::IOFile out;
+    u64 cursor = 0;
+    u64 resume_end = 0;
+    std::vector<size_t> chunk;
+    u64 chunk_bytes = 0;
+    std::vector<u8> buffer;
+    std::vector<u8> out_buffer;
+    Sha256 hash;
+    std::unique_ptr<ZstdContext> compressor;
+    PackProgress progress{};
+    u64 last_report = 0;
+    u64 file_counted = 0;
+};
+
+} // namespace
+
+bool IsLooseDump(const fs::path& dir) {
+    return HasBootableExeFS(dir);
+}
+
+std::optional<fs::path> DumpRootFromMain(const fs::path& main) {
+    // The Qt game list stores the exefs folder rather than exefs/main.
+    std::error_code ec;
+    const auto exefs = fs::is_directory(main, ec) ? main : main.parent_path();
+    if (Lower(ToUtf8(exefs.filename())) != "exefs") {
+        return std::nullopt;
+    }
+    auto root = exefs.parent_path();
+    const auto name = Lower(ToUtf8(root.filename()));
+    if (name == "base") {
+        root = root.parent_path();
+    } else if (ParseDecimal(name) && Lower(ToUtf8(root.parent_path().filename())) == "updates") {
+        root = root.parent_path().parent_path();
+    }
+    if (!IsLooseDump(root)) {
+        return std::nullopt;
+    }
+    return root;
+}
+
+fs::path DefaultArchivePath(const fs::path& dump_root) {
+    auto root = dump_root;
+    if (!root.has_filename()) {
+        root = root.parent_path();
+    }
+    return root.parent_path() / (root.filename().u8string() + u8".nup");
+}
+
+bool HasResumableJournal(const fs::path& archive) {
+    std::error_code ec;
+    return fs::exists(WithSuffix(archive, ".part"), ec) &&
+           fs::exists(WithSuffix(archive, ".journal"), ec);
+}
+
+PackResult PackDump(const fs::path& dump_root, const fs::path& archive, const PackOptions& options,
+                    const std::function<void(const PackProgress&)>& progress,
+                    const std::atomic_bool* cancel, std::string* error_out) {
+    Packer packer{dump_root, archive, options, progress, cancel};
+    try {
+        return packer.Run();
+    } catch (const PackError& e) {
+        packer.Abort();
+        if (error_out) {
+            *error_out = e.what();
+        }
+        return e.result;
+    } catch (const std::exception& e) {
+        packer.Abort();
+        if (error_out) {
+            *error_out = e.what();
+        }
+        return PackResult::IoError;
+    }
+}
+
+} // namespace FileSys::Nup
diff --git a/src/core/file_sys/nup_writer.h b/src/core/file_sys/nup_writer.h
new file mode 100644
index 0000000000..231387b156
--- /dev/null
+++ b/src/core/file_sys/nup_writer.h
@@ -0,0 +1,60 @@
+// SPDX-FileCopyrightText: Copyright 2026 Eden Emulator Project
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#pragma once
+
+#include <atomic>
+#include <filesystem>
+#include <functional>
+#include <optional>
+#include <string>
+
+#include "common/common_types.h"
+
+// Packs a loose dump into a NUP container. Every package is kept: base/, each
+// updates/<version>/ and each dlc/<titleid>/<n>/.
+namespace FileSys::Nup {
+
+struct PackProgress {
+    u64 bytes_done{};
+    u64 bytes_total{};
+    u64 files_done{};
+    u64 files_total{};
+};
+
+enum class PackResult { Success, Cancelled, InvalidSource, IoError };
+
+// NupContainer keeps a zstd file in memory only while it fits its 512 MiB decompression cache;
+// a larger one is decompressed again in full on every read, which makes big compressed RomFS
+// files unusable. Files above this size are therefore stored raw, with headroom below the cap so
+// that one file does not evict everything else from the cache.
+constexpr u64 DefaultRawThreshold = 256ULL * 1024 * 1024;
+
+struct PackOptions {
+    // Low-storage mode: delete each source file once its extent is synced and journaled.
+    bool delete_sources = false;
+    u64 chunk_bytes = 256ULL * 1024 * 1024;
+    int zstd_level = 3;
+    // Files larger than this are always stored raw.
+    u64 raw_threshold = DefaultRawThreshold;
+};
+
+// A loose dump holds exefs/main and main.npdm, directly or under base/ or updates/<version>/,
+// and a romfs folder. Folder names are matched case-insensitively.
+bool IsLooseDump(const std::filesystem::path& dir);
+// The dump folder a game list entry's exefs/main (or exefs folder) belongs to, if it is a loose
+// dump.
+std::optional<std::filesystem::path> DumpRootFromMain(const std::filesystem::path& main);
+std::filesystem::path DefaultArchivePath(const std::filesystem::path& dump_root);
+
+// Writes <archive>.part and renames it when done; an existing archive is never overwritten. A
+// cancelled or failed low-storage run keeps its .part and .journal, and calling this again with
+// the same arguments resumes it.
+PackResult PackDump(const std::filesystem::path& dump_root, const std::filesystem::path& archive,
+                    const PackOptions& options = {},
+                    const std::function<void(const PackProgress&)>& progress = {},
+                    const std::atomic_bool* cancel = nullptr, std::string* error_out = nullptr);
+
+bool HasResumableJournal(const std::filesystem::path& archive);
+
+} // namespace FileSys::Nup
diff --git a/src/core/launch_params.cpp b/src/core/launch_params.cpp
index 25fdd45fdb..6c436d0346 100644
--- a/src/core/launch_params.cpp
+++ b/src/core/launch_params.cpp
@@ -39,6 +39,7 @@ LaunchParams ParseLaunchParams(Core::System& system, int argc, char *argv[], wch
         {"null-render", no_argument, 0, 'n'},
         {"singlecore", no_argument, 0, 's'},
         {"filter", no_argument, 0, 'x'},
+        {"pack-nup", required_argument, 0, 'N'},
         {0, 0, 0, 0},
         // clang-format on
     };
@@ -62,6 +63,9 @@ LaunchParams ParseLaunchParams(Core::System& system, int argc, char *argv[], wch
             case 'g':
                 p.filepath = std::string(optarg);
                 break;
+            case 'N':
+                p.pack_nup_source = std::string(optarg);
+                break;
             case 'i': {
                 p.input_profile = std::string(optarg);
                 break;
@@ -196,7 +200,9 @@ void ApplyLaunchParams(LaunchParams const& lp) noexcept {
             "-p, --program         Pass following string as arguments to executable\n"
             "-u, --user            Select a specific user profile from 0 to 7\n"
             "-d, --debug           Run the GDB stub on a port from 1 to 65535\n"
-            "-v, --version         Output version information and exit\n",
+            "-v, --version         Output version information and exit\n"
+            "--pack-nup <dump> [<out.nup>]"
+            " Pack a loose dump with all its updates and DLC into a NUP file and exit\n",
             lp.argv0
         );
     }
diff --git a/src/core/launch_params.h b/src/core/launch_params.h
index 4da30fc1c2..8d503770d8 100644
--- a/src/core/launch_params.h
+++ b/src/core/launch_params.h
@@ -23,6 +23,8 @@ struct LaunchParams {
     std::optional<int> selected_user{};
     std::optional<u16> override_gdb_port{};
     std::optional<std::string> log_filter{};
+    // --pack-nup <dump> [<out.nup>]: packs a loose dump instead of booting a game (eden-cli).
+    std::optional<std::string> pack_nup_source{};
     u16 port = Network::DefaultRoomPort;
     bool use_multiplayer = false;
     bool fullscreen = false;
diff --git a/src/tests/CMakeLists.txt b/src/tests/CMakeLists.txt
index 194e90a243..a9be2ec7a8 100644
--- a/src/tests/CMakeLists.txt
+++ b/src/tests/CMakeLists.txt
@@ -17,6 +17,7 @@ add_executable(tests
     common/undefined_fix.cpp
     common/unique_function.cpp
     core/core_timing.cpp
+    core/nup_writer.cpp
     core/internal_network/network.cpp
     video_core/memory_tracker.cpp
     video_core/vertex_repack.cpp
diff --git a/src/tests/core/nup_writer.cpp b/src/tests/core/nup_writer.cpp
new file mode 100644
index 0000000000..ce1a0717ed
--- /dev/null
+++ b/src/tests/core/nup_writer.cpp
@@ -0,0 +1,392 @@
+// SPDX-FileCopyrightText: Copyright 2026 Eden Emulator Project
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#include <catch2/catch_test_macros.hpp>
+
+#include <array>
+#include <atomic>
+#include <chrono>
+#include <filesystem>
+#include <fstream>
+#include <iterator>
+#include <map>
+#include <string>
+#include <vector>
+
+#include <fmt/format.h>
+#include <openssl/evp.h>
+
+#include "core/file_sys/nup_container.h"
+#include "core/file_sys/nup_writer.h"
+#include "core/file_sys/vfs/vfs_real.h"
+
+namespace {
+
+namespace fs = std::filesystem;
+using FileSys::NupContainer;
+
+struct TempDir {
+    fs::path path = fs::temp_directory_path() /
+                    ("nup-test-" +
+                     std::to_string(std::chrono::steady_clock::now().time_since_epoch().count()));
+    TempDir() {
+        fs::create_directories(path);
+    }
+    ~TempDir() {
+        std::error_code ec;
+        fs::remove_all(path, ec);
+    }
+};
+
+void Put(const fs::path& p, std::string_view value) {
+    fs::create_directories(p.parent_path());
+    std::ofstream(p, std::ios::binary) << value;
+}
+
+std::string ReadAll(const fs::path& p) {
+    std::ifstream in(p, std::ios::binary);
+    return {std::istreambuf_iterator<char>(in), {}};
+}
+
+std::string Read(const FileSys::VirtualFile& f) {
+    std::string out(f->GetSize(), '\0');
+    f->Read(reinterpret_cast<u8*>(out.data()), out.size(), 0);
+    return out;
+}
+
+// Enough of an NPDM for the packer: the program ID at ACI0 + 0x10.
+std::string Npdm(u64 program_id) {
+    std::string npdm(0x100, '\0');
+    npdm.replace(0x80, 4, "ACI0");
+    for (int i = 0; i < 8; ++i) {
+        npdm[0x90 + i] = static_cast<char>(program_id >> (8 * i));
+    }
+    return npdm;
+}
+
+std::array<u8, 32> Sha256(std::string_view data) {
+    std::array<u8, 32> out{};
+    unsigned int length{};
+    EVP_Digest(data.data(), data.size(), out.data(), &length, EVP_sha256(), nullptr);
+    return out;
+}
+
+u64 Le(const std::string& buf, size_t at, size_t bytes) {
+    u64 value = 0;
+    for (size_t i = 0; i < bytes; ++i) {
+        value |= static_cast<u64>(static_cast<u8>(buf[at + i])) << (8 * i);
+    }
+    return value;
+}
+
+struct RawFile {
+    std::string name;
+    u64 size;
+    std::array<u8, 32> sha256;
+    u64 extent_offset;
+    u64 extent_size;
+    u8 codec;
+};
+
+// Reads the file records straight from the TOC, which NupContainer does not expose.
+std::vector<RawFile> RawFiles(const std::string& nup) {
+    const u64 toc = Le(nup, 0x08, 8);
+    const u64 packages = Le(nup, toc + 0x04, 4);
+    const u64 dirs = Le(nup, toc + 0x08, 8);
+    const u64 files = Le(nup, toc + 0x10, 8);
+    const u64 pool = toc + Le(nup, toc + 0x18, 8);
+    std::vector<RawFile> out;
+    u64 pos = toc + 0x30 + packages * 0x40 + dirs * 0x18;
+    for (u64 i = 0; i < files; ++i, pos += 0x50) {
+        RawFile file{nup.substr(pool + Le(nup, pos, 4), Le(nup, pos + 4, 4)),
+                     Le(nup, pos + 0x08, 8),
+                     {},
+                     Le(nup, pos + 0x10, 8),
+                     Le(nup, pos + 0x18, 8),
+                     static_cast<u8>(nup[pos + 0x40])};
+        std::copy_n(nup.begin() + static_cast<std::ptrdiff_t>(pos + 0x20), 32,
+                    file.sha256.begin());
+        out.push_back(file);
+    }
+    return out;
+}
+
+// Every file under `dir` with its contents, keyed by its path relative to `dir`.
+std::map<std::string, std::string> SourceTree(const fs::path& dir) {
+    std::map<std::string, std::string> out;
+    for (const auto& entry : fs::recursive_directory_iterator(dir)) {
+        if (entry.is_regular_file() && entry.path().filename() != ".listing") {
+            out[fs::relative(entry.path(), dir).generic_string()] = ReadAll(entry.path());
+        }
+    }
+    return out;
+}
+
+void PackedTree(const FileSys::VirtualDir& dir, const std::string& prefix,
+                std::map<std::string, std::string>& out) {
+    if (dir == nullptr) {
+        return;
+    }
+    for (const auto& file : dir->GetFiles()) {
+        out[prefix + file->GetName()] = Read(file);
+    }
+    for (const auto& sub : dir->GetSubdirectories()) {
+        PackedTree(sub, prefix + sub->GetName() + "/", out);
+    }
+}
+
+std::map<std::string, std::string> PackedTree(const FileSys::VirtualDir& dir) {
+    std::map<std::string, std::string> out;
+    PackedTree(dir, "", out);
+    return out;
+}
+
+constexpr u64 TitleId = 0x0400ABCD00010000ULL;
+
+void MakeDump(const fs::path& root) {
+    Put(root / "Base/ExeFS/main", "base main");
+    Put(root / "Base/ExeFS/main.npdm", Npdm(TitleId));
+    Put(root / "Base/RomFS/shared.bin", std::string(5000, 's'));
+    Put(root / "Base/RomFS/copy/shared.bin", std::string(5000, 's'));
+    Put(root / "Base/RomFS/empty", "");
+    Put(root / "Base/RomFS/.listing", "listing");
+    Put(root / "Base/RomFS/System/Resource/ResourceSizeTable.Product.100.rsizetable", "rst");
+    Put(root / "Base/RomFS/big.bin", std::string(64 * 1024, 'b'));
+    Put(root / "Base/RomFS/random.bin", [] {
+        std::string data(3000, '\0');
+        u32 x = 12345;
+        for (auto& c : data) {
+            x = x * 1664525 + 1013904223;
+            c = static_cast<char>(x >> 24);
+        }
+        return data;
+    }());
+    Put(root / "updates/65536/exefs/main", "update main");
+    Put(root / "updates/65536/exefs/main.npdm", Npdm(TitleId));
+    Put(root / "updates/65536/romfs/shared.bin", std::string(5000, 's'));
+    Put(root / "updates/65536/romfs/System/Resource/ResourceSizeTable.Product.110.rsizetable",
+        "rst");
+    Put(root / "updates/65536/romfs/Zeta/a", "a");
+    Put(root / "updates/65536/romfs/alpha", "alpha");
+    Put(root / "updates/131072/exefs/main", "update 2 main");
+    Put(root / "updates/131072/exefs/main.npdm", Npdm(TitleId));
+    Put(root / "dlc/0400ABCD00011001/0/romfs/addon.bin", "addon data");
+}
+
+} // namespace
+
+TEST_CASE("NUP packs base, updates and add-ons and reads back through NupContainer", "[nup]") {
+    TempDir t;
+    const auto root = t.path / "Game";
+    MakeDump(root);
+    const auto archive = t.path / "Game.nup";
+    FileSys::Nup::PackOptions options{.raw_threshold = 16 * 1024};
+    std::string error;
+    REQUIRE(FileSys::Nup::PackDump(root, archive, options, {}, nullptr, &error) ==
+            FileSys::Nup::PackResult::Success);
+    INFO(error);
+    REQUIRE_FALSE(fs::exists(archive.string() + ".part"));
+
+    FileSys::RealVfsFilesystem real;
+    NupContainer nup{real.OpenFile(archive.string(), FileSys::OpenMode::Read)};
+    REQUIRE(nup.GetStatus() == Loader::ResultStatus::Success);
+    REQUIRE(nup.VerifyIntegrity({}) == Loader::ResultStatus::Success);
+
+    const auto& packages = nup.GetPackages();
+    REQUIRE(packages.size() == 4);
+    REQUIRE(packages[0].kind == NupContainer::PackageKind::Base);
+    REQUIRE(packages[0].title_id == TitleId);
+    REQUIRE(packages[0].version == 0);
+    REQUIRE(packages[0].npdm.size() == 0x100);
+    REQUIRE(packages[1].kind == NupContainer::PackageKind::Update);
+    REQUIRE(packages[1].version == 65536);
+    REQUIRE(packages[1].title_id == TitleId);
+    REQUIRE_FALSE(packages[1].standalone_update);
+    REQUIRE(packages[2].kind == NupContainer::PackageKind::Update);
+    REQUIRE(packages[2].version == 131072);
+    REQUIRE(packages[2].romfs_dir == 0xFFFFFFFF);
+    REQUIRE(packages[3].kind == NupContainer::PackageKind::Addon);
+    REQUIRE(packages[3].title_id == 0x0400ABCD00011001ULL);
+    REQUIRE(packages[3].exefs_dir == 0xFFFFFFFF);
+    REQUIRE(nup.FindBestUpdatePackage() == 2);
+
+    REQUIRE(PackedTree(nup.GetExeFSDir(0)) == SourceTree(root / "Base/ExeFS"));
+    REQUIRE(PackedTree(nup.GetRomFSDir(0)) == SourceTree(root / "Base/RomFS"));
+    REQUIRE(PackedTree(nup.GetExeFSDir(1)) == SourceTree(root / "updates/65536/exefs"));
+    REQUIRE(PackedTree(nup.GetRomFSDir(1)) == SourceTree(root / "updates/65536/romfs"));
+    REQUIRE(PackedTree(nup.GetExeFSDir(2)) == SourceTree(root / "updates/131072/exefs"));
+    REQUIRE(PackedTree(nup.GetRomFSDir(3)) == SourceTree(root / "dlc/0400ABCD00011001/0/romfs"));
+    REQUIRE_FALSE(nup.GetRomFSDir(0)->GetFile(".listing"));
+
+    const auto bytes = ReadAll(archive);
+    const auto files = RawFiles(bytes);
+    std::map<std::string, std::vector<RawFile>> by_name;
+    for (const auto& file : files) {
+        by_name[file.name].push_back(file);
+        if (file.size != 0) {
+            REQUIRE(file.extent_offset % 16 == 0);
+        }
+    }
+    const auto shared = by_name.at("shared.bin");
+    REQUIRE(shared.size() == 3);
+    for (const auto& file : shared) {
+        REQUIRE(file.sha256 == Sha256(std::string(5000, 's')));
+        REQUIRE(file.codec == 1);
+        REQUIRE(file.extent_offset == shared[0].extent_offset);
+        REQUIRE(file.extent_size == shared[0].extent_size);
+    }
+    const auto& empty = by_name.at("empty").at(0);
+    REQUIRE(empty.size == 0);
+    REQUIRE(empty.extent_offset == 0);
+    REQUIRE(empty.extent_size == 0);
+    REQUIRE(empty.codec == 0);
+    REQUIRE(empty.sha256 == Sha256(""));
+    // Highly compressible, but above the raw threshold.
+    const auto& big = by_name.at("big.bin").at(0);
+    REQUIRE(big.codec == 0);
+    REQUIRE(big.extent_size == 64 * 1024);
+    REQUIRE(big.sha256 == Sha256(std::string(64 * 1024, 'b')));
+    // Incompressible, so stored raw.
+    const auto& random = by_name.at("random.bin").at(0);
+    REQUIRE(random.codec == 0);
+    REQUIRE(random.extent_size == 3000);
+    REQUIRE_FALSE(by_name.contains(".listing"));
+}
+
+TEST_CASE("NUP marks updates standalone when the dump has no base", "[nup]") {
+    TempDir t;
+    const auto root = t.path / "Game";
+    Put(root / "updates/65536/exefs/main", "main");
+    Put(root / "updates/65536/exefs/main.npdm", Npdm(TitleId));
+    Put(root / "updates/65536/romfs/file", "rom");
+    const auto archive = t.path / "Game.nup";
+    REQUIRE(FileSys::Nup::PackDump(root, archive) == FileSys::Nup::PackResult::Success);
+
+    FileSys::RealVfsFilesystem real;
+    NupContainer nup{real.OpenFile(archive.string(), FileSys::OpenMode::Read)};
+    REQUIRE(nup.GetStatus() == Loader::ResultStatus::Success);
+    REQUIRE(nup.GetPackages().size() == 1);
+    REQUIRE(nup.GetPackages()[0].kind == NupContainer::PackageKind::Update);
+    REQUIRE(nup.GetPackages()[0].standalone_update);
+    REQUIRE(nup.GetPackages()[0].title_id == TitleId);
+    REQUIRE(Read(nup.GetRomFSDir(0)->GetFile("file")) == "rom");
+}
+
+TEST_CASE("NUP packs a bare exefs/romfs dump as one base", "[nup]") {
+    TempDir t;
+    const auto root = t.path / "Game";
+    Put(root / "ExeFS/main", "main");
+    Put(root / "ExeFS/main.npdm", Npdm(TitleId));
+    Put(root / "RomFS/file", "rom");
+    Put(root / "notes.txt", "extra");
+    const auto archive = t.path / "Game.nup";
+    REQUIRE(FileSys::Nup::PackDump(root, archive) == FileSys::Nup::PackResult::Success);
+
+    FileSys::RealVfsFilesystem real;
+    NupContainer nup{real.OpenFile(archive.string(), FileSys::OpenMode::Read)};
+    REQUIRE(nup.GetStatus() == Loader::ResultStatus::Success);
+    REQUIRE(nup.GetPackages().size() == 1);
+    REQUIRE(nup.GetPackages()[0].kind == NupContainer::PackageKind::Base);
+    REQUIRE_FALSE(nup.GetPackages()[0].standalone_update);
+    REQUIRE(Read(nup.GetExeFSDir(0)->GetFile("main")) == "main");
+    REQUIRE(Read(nup.GetRomFSDir(0)->GetFile("file")) == "rom");
+    const auto files = RawFiles(ReadAll(archive));
+    REQUIRE(std::ranges::count(files, std::string{"notes.txt"}, &RawFile::name) == 1);
+}
+
+TEST_CASE("NUP low storage resumes and deletes the packed sources", "[nup]") {
+    TempDir t;
+    const auto root = t.path / "Game";
+    MakeDump(root);
+    const auto copy = t.path / "copy" / "Game";
+    fs::create_directories(copy);
+    fs::copy(root, copy, fs::copy_options::recursive);
+    const auto archive = t.path / "Game.nup";
+
+    std::atomic_bool cancel = false;
+    bool cancelled = false;
+    FileSys::Nup::PackOptions options{.delete_sources = true, .chunk_bytes = 1};
+    auto result = FileSys::Nup::PackDump(
+        root, archive, options,
+        [&](const auto& p) {
+            if (p.files_done >= 4 && !cancelled) {
+                cancel = true;
+                cancelled = true;
+            }
+        },
+        &cancel);
+    REQUIRE(result == FileSys::Nup::PackResult::Cancelled);
+    REQUIRE(FileSys::Nup::HasResumableJournal(archive));
+    REQUIRE_FALSE(fs::exists(root / "Base/ExeFS/main"));
+    REQUIRE_FALSE(fs::exists(root / "Base/ExeFS/main.npdm"));
+
+    cancel = false;
+    std::string error;
+    REQUIRE(FileSys::Nup::PackDump(root, archive, options, {}, &cancel, &error) ==
+            FileSys::Nup::PackResult::Success);
+    INFO(error);
+    REQUIRE_FALSE(fs::exists(archive.string() + ".journal"));
+    REQUIRE_FALSE(fs::exists(archive.string() + ".part"));
+    REQUIRE_FALSE(fs::exists(root / "Base/ExeFS"));
+    REQUIRE_FALSE(fs::exists(root / "updates"));
+    REQUIRE_FALSE(fs::exists(root / "dlc"));
+    // The listing is not packed, so it is left behind with the folders holding it.
+    REQUIRE(ReadAll(root / "Base/RomFS/.listing") == "listing");
+    REQUIRE_FALSE(fs::exists(root / "Base/RomFS/shared.bin"));
+
+    FileSys::RealVfsFilesystem real;
+    NupContainer nup{real.OpenFile(archive.string(), FileSys::OpenMode::Read)};
+    REQUIRE(nup.GetStatus() == Loader::ResultStatus::Success);
+    REQUIRE(nup.VerifyIntegrity({}) == Loader::ResultStatus::Success);
+    REQUIRE(nup.GetPackages().size() == 4);
+    const auto npdm = Npdm(TitleId);
+    REQUIRE(nup.GetPackages()[0].npdm == std::vector<u8>(npdm.begin(), npdm.end()));
+    REQUIRE(PackedTree(nup.GetRomFSDir(0)) == SourceTree(copy / "Base/RomFS"));
+    REQUIRE(PackedTree(nup.GetRomFSDir(1)) == SourceTree(copy / "updates/65536/romfs"));
+
+    // The resumed archive matches one packed in a single pass.
+    const auto again = t.path / "again.nup";
+    REQUIRE(FileSys::Nup::PackDump(copy, again) == FileSys::Nup::PackResult::Success);
+    REQUIRE(ReadAll(archive) == ReadAll(again));
+}
+
+TEST_CASE("NUP rejects overwrite and a dump without NPDM", "[nup]") {
+    TempDir t;
+    const auto root = t.path / "Game";
+    Put(root / "exefs/main", "main");
+    Put(root / "romfs/a", "rom");
+    const auto archive = t.path / "out.nup";
+    Put(archive, "existing");
+    REQUIRE(FileSys::Nup::PackDump(root, archive) == FileSys::Nup::PackResult::IoError);
+    REQUIRE(ReadAll(archive) == "existing");
+    fs::remove(archive);
+    REQUIRE(FileSys::Nup::PackDump(root, archive) == FileSys::Nup::PackResult::InvalidSource);
+    REQUIRE_FALSE(fs::exists(archive.string() + ".part"));
+}
+
+// Archives are meant to be byte-identical on every platform. A change to this hash means
+// packing a dump no longer reproduces archives made by earlier builds (for example after a zstd
+// update), so make it deliberately.
+TEST_CASE("NUP output is reproducible", "[nup]") {
+    TempDir t;
+    const auto root = t.path / "Game";
+    MakeDump(root);
+    // Large and compressible, so it covers what used to be zstd's multithreaded path.
+    Put(root / "Base/RomFS/large.bin", [] {
+        std::string data(20 * 1024 * 1024, '\0');
+        u32 x = 1;
+        for (auto& c : data) {
+            x = x * 1664525 + 1013904223;
+            c = static_cast<char>('a' + (x >> 28));
+        }
+        return data;
+    }());
+    const auto archive = t.path / "Game.nup";
+    REQUIRE(FileSys::Nup::PackDump(root, archive) == FileSys::Nup::PackResult::Success);
+
+    std::string hex;
+    for (const u8 b : Sha256(ReadAll(archive))) {
+        hex += fmt::format("{:02x}", b);
+    }
+    REQUIRE(hex == "df8446903ab2c39a51af0304935eb4aa5d8ead105440976ceae7ab97133f6143");
+}
diff --git a/src/yuzu/game/game_list.cpp b/src/yuzu/game/game_list.cpp
index cd7fc19de4..8e3eb7bc52 100644
--- a/src/yuzu/game/game_list.cpp
+++ b/src/yuzu/game/game_list.cpp
@@ -24,6 +24,7 @@
 
 #include "common/common_types.h"
 #include "core/core.h"
+#include "core/file_sys/nup_writer.h"
 #include "core/file_sys/patch_manager.h"
 #include "core/file_sys/registered_cache.h"
 #include "qt_common/config/uisettings.h"
@@ -99,6 +100,10 @@ GameList::GameList(FileSys::VirtualFilesystem vfs_, FileSys::ManualContentProvid
     ResetViewMode();
 }
 
+void GameList::SetNupConversionRunning(bool running) {
+    nup_conversion_running = running;
+}
+
 GameList::~GameList() {
     UnloadController();
 }
@@ -477,6 +482,11 @@ void GameList::AddGamePopup(QMenu& context_menu, u64 program_id, const std::stri
     QAction* dump_romfs_sdmc = dump_romfs_menu->addAction(tr("Dump RomFS to SDMC"));
     QAction* verify_integrity = context_menu.addAction(tr("Verify Integrity"));
     QAction* copy_tid = context_menu.addAction(tr("Copy Title ID to Clipboard"));
+    QAction* convert_nup = nullptr;
+    if (FileSys::Nup::DumpRootFromMain(path)) {
+        convert_nup = context_menu.addAction(tr("Convert to NUP..."));
+        convert_nup->setEnabled(!nup_conversion_running);
+    }
 #if !defined(__APPLE__)
     QMenu* shortcut_menu = context_menu.addMenu(tr("Create Shortcut"));
     QAction* create_desktop_shortcut = shortcut_menu->addAction(tr("Add to Desktop"));
@@ -557,6 +567,10 @@ void GameList::AddGamePopup(QMenu& context_menu, u64 program_id, const std::stri
             [this, path]() { emit VerifyIntegrityRequested(path); });
     connect(copy_tid, &QAction::triggered, this,
             [this, program_id]() { emit CopyTIDRequested(program_id); });
+    if (convert_nup) {
+        connect(convert_nup, &QAction::triggered, this,
+                [this, path]() { emit ConvertToNupRequested(path); });
+    }
 #if !defined(__APPLE__)
     connect(create_desktop_shortcut, &QAction::triggered, this, [this, program_id, path]() {
         emit CreateShortcut(program_id, path, QtCommon::Game::ShortcutTarget::Desktop);
diff --git a/src/yuzu/game/game_list.h b/src/yuzu/game/game_list.h
index 1540dd9cf0..67713691fd 100644
--- a/src/yuzu/game/game_list.h
+++ b/src/yuzu/game/game_list.h
@@ -88,6 +88,7 @@ public:
     void ResetViewMode();
 
 public slots:
+    void SetNupConversionRunning(bool running);
     void RefreshGameDirectory();
     void RefreshExternalContent();
     void UpdateIconSizes();
@@ -106,6 +107,7 @@ signals:
     void SetPlayTimeRequested(u64 program_id);
     void DumpRomFSRequested(u64 program_id, const std::string& game_path, DumpRomFSTarget target);
     void VerifyIntegrityRequested(const std::string& game_path);
+    void ConvertToNupRequested(const std::string& game_path);
     void CopyTIDRequested(u64 program_id);
     void CreateShortcut(u64 program_id, const std::string& game_path,
                         const QtCommon::Game::ShortcutTarget target);
@@ -165,6 +167,7 @@ private:
     Core::System& system;
 
     bool m_isTreeMode = true;
+    bool nup_conversion_running{};
     QAbstractItemView* m_currentView = nullptr;
 };
 
diff --git a/src/yuzu/main_window.cpp b/src/yuzu/main_window.cpp
index b0c0446add..2b43bcd2d0 100644
--- a/src/yuzu/main_window.cpp
+++ b/src/yuzu/main_window.cpp
@@ -149,6 +149,7 @@ static FileSys::VirtualFile VfsDirectoryCreateFileWrapper(const FileSys::Virtual
 
 #include "core/file_sys/card_image.h"
 #include "core/file_sys/common_funcs.h"
+#include "core/file_sys/nup_writer.h"
 #include "core/file_sys/romfs.h"
 #include "core/file_sys/savedata_factory.h"
 
@@ -554,6 +555,10 @@ MainWindow::MainWindow(bool has_broken_vulkan)
 }
 
 MainWindow::~MainWindow() {
+    if (nup_cancel) {
+        nup_cancel->store(true);
+    }
+    nup_watcher.waitForFinished();
 #ifdef __APPLE__
     AllowOSSleep();
 #endif
@@ -1458,6 +1463,8 @@ void MainWindow::ConnectWidgetEvents() {
     connect(game_list, &GameList::DumpRomFSRequested, this, &MainWindow::OnGameListDumpRomFS);
     connect(game_list, &GameList::VerifyIntegrityRequested, this,
             &MainWindow::OnGameListVerifyIntegrity);
+    connect(game_list, &GameList::ConvertToNupRequested, this,
+            &MainWindow::OnGameListConvertToNup);
     connect(game_list, &GameList::CopyTIDRequested, this, &MainWindow::OnGameListCopyTID);
     connect(game_list, &GameList::CreateShortcut, this, &MainWindow::OnGameListCreateShortcut);
     connect(game_list, &GameList::AddDirectory, this, &MainWindow::OnGameListAddDirectory);
@@ -1907,6 +1914,12 @@ bool MainWindow::SelectAndSetCurrentUser(
 
 void MainWindow::BootGame(const QString& filename, Service::AM::FrontendAppletParameters params,
                           StartGameType type) {
+    if (nup_running && filename.toStdString() == nup_source_path) {
+        QMessageBox::information(this, tr("Conversion in Progress"),
+                                 tr("This game cannot be started while its dump is being "
+                                    "converted."));
+        return;
+    }
     LOG_INFO(Frontend, "Eglantine starting...");
 
     if (params.program_id == 0 ||
@@ -3967,6 +3980,151 @@ void MainWindow::OnGameListRefresh() {
     SetFirmwareVersion();
 }
 
+void MainWindow::OnGameListConvertToNup(const std::string& game_path) {
+    if (nup_running)
+        return;
+
+    const auto root = FileSys::Nup::DumpRootFromMain(game_path);
+    if (!root)
+        return;
+    const QString convert_title = tr("Convert to NUP");
+    const auto archive = FileSys::Nup::DefaultArchivePath(*root);
+    if (std::filesystem::exists(archive)) {
+        QMessageBox::information(this, convert_title,
+                                 tr("The target archive already exists:\n%1")
+                                     .arg(QString::fromStdString(Common::FS::PathToUTF8String(archive))));
+        return;
+    }
+
+    const bool resume = FileSys::Nup::HasResumableJournal(archive);
+    bool delete_sources = resume;
+    if (resume) {
+        if (QMessageBox::question(this, tr("Resume Conversion"),
+                                  tr("Resume the interrupted conversion?"),
+                                  QMessageBox::Yes | QMessageBox::No) != QMessageBox::Yes)
+            return;
+    } else {
+        QMessageBox prompt(QMessageBox::Question, convert_title,
+                           tr("Source folder:\n%1\n\nTarget archive:\n%2")
+                               .arg(QString::fromStdString(Common::FS::PathToUTF8String(*root)),
+                                    QString::fromStdString(Common::FS::PathToUTF8String(archive))),
+                           QMessageBox::Yes | QMessageBox::No, this);
+        // QMessageBox takes ownership of its check box.
+        auto* low_storage = new QCheckBox(tr("Low storage: delete the original files as they "
+                                             "are packed (cannot be undone)"));
+        prompt.setCheckBox(low_storage);
+        u64 needed{};
+        {
+            std::error_code ec;
+            for (std::filesystem::recursive_directory_iterator it(*root, ec), end;
+                 !ec && it != end; it.increment(ec)) {
+                if (it->is_regular_file(ec))
+                    needed += it->file_size(ec);
+            }
+        }
+        std::error_code space_error;
+        const auto space = std::filesystem::space(archive.parent_path(), space_error);
+        const auto to_mb = [](u64 bytes) { return bytes / (1024 * 1024); };
+        const QString space_info = tr("\n\nApproximate space needed: %1 MB\nFree space on target "
+                                      "volume: %2 MB")
+                                       .arg(to_mb(needed))
+                                       .arg(space_error ? 0 : to_mb(space.available));
+        prompt.setInformativeText(space_info);
+        if (!space_error && space.available < needed) {
+            prompt.setText(prompt.text() + tr("\n\nWarning: free space is less than the "
+                                              "estimated space needed."));
+        }
+        if (prompt.exec() != QMessageBox::Yes)
+            return;
+        delete_sources = low_storage->isChecked();
+    }
+
+    nup_running = true;
+    nup_source_path = game_path;
+    game_list->SetNupConversionRunning(true);
+    nup_cancel = std::make_shared<std::atomic_bool>(false);
+    nup_progress =
+        new QProgressDialog(tr("Preparing conversion..."), tr("Cancel"), 0, 1000, this);
+    nup_progress->setWindowTitle(tr("Converting to NUP"));
+    nup_progress->setMinimumDuration(0);
+    nup_progress->setAutoClose(false);
+    nup_progress->setAutoReset(false);
+    connect(nup_progress, &QProgressDialog::canceled, this,
+            [cancel = nup_cancel] { cancel->store(true); });
+    nup_progress->show();
+
+    const auto cancel = nup_cancel;
+    auto last_update = std::make_shared<std::chrono::steady_clock::time_point>();
+    nup_watcher.setFuture(QtConcurrent::run([this, root = *root, archive, delete_sources,
+                                                  cancel, last_update] {
+        std::string error;
+        const auto on_progress = [this, last_update](
+                                     const FileSys::Nup::PackProgress& progress) {
+                const auto now = std::chrono::steady_clock::now();
+                if (now - *last_update < std::chrono::milliseconds(200))
+                    return;
+                *last_update = now;
+                QMetaObject::invokeMethod(
+                    this,
+                    [this, progress] {
+                        if (!nup_progress)
+                            return;
+                        const auto percent = progress.bytes_total == 0
+                                                 ? 0
+                                                 : static_cast<int>(progress.bytes_done * 1000 /
+                                                                    progress.bytes_total);
+                        nup_progress->setValue(percent);
+                        nup_progress->setLabelText(
+                            tr("%1 / %2 MB\n%3 / %4 files")
+                                .arg(progress.bytes_done / (1024 * 1024))
+                                .arg(progress.bytes_total / (1024 * 1024))
+                                .arg(progress.files_done)
+                                .arg(progress.files_total));
+                    },
+                    Qt::QueuedConnection);
+        };
+        const auto result = FileSys::Nup::PackDump(
+            root, archive, {.delete_sources = delete_sources}, on_progress, cancel.get(), &error);
+        QMetaObject::invokeMethod(
+            this,
+            [this, result, delete_sources, error] {
+                nup_running = false;
+                nup_source_path.clear();
+                game_list->SetNupConversionRunning(false);
+                if (nup_progress) {
+                    nup_progress->close();
+                    nup_progress->deleteLater();
+                    nup_progress = nullptr;
+                }
+                nup_cancel.reset();
+                switch (result) {
+                case FileSys::Nup::PackResult::Success:
+                    QMessageBox::information(
+                        this, tr("Conversion Complete"),
+                        delete_sources ? tr("The NUP was created and the loose folder was "
+                                            "removed.")
+                                       : tr("The NUP was created. You can delete the loose "
+                                            "folder if you no longer need it."));
+                    OnGameListRefresh();
+                    break;
+                case FileSys::Nup::PackResult::Cancelled:
+                    if (delete_sources)
+                        QMessageBox::information(this, tr("Conversion Cancelled"),
+                                                 tr("The conversion can be resumed by choosing "
+                                                    "Convert to NUP again."));
+                    break;
+                case FileSys::Nup::PackResult::InvalidSource:
+                case FileSys::Nup::PackResult::IoError:
+                    QMessageBox::critical(this, tr("Conversion Failed"),
+                                          QString::fromStdString(error));
+                    break;
+                }
+            },
+            Qt::QueuedConnection);
+        return result;
+    }));
+}
+
 void MainWindow::LaunchFirmwareApplet(u64 raw_program_id,
                                       std::optional<Service::NFP::CabinetMode> cabinet_mode) {
     auto const program_id = Service::AM::AppletProgramId(raw_program_id);
diff --git a/src/yuzu/main_window.h b/src/yuzu/main_window.h
index 57f585fef9..11732ff242 100644
--- a/src/yuzu/main_window.h
+++ b/src/yuzu/main_window.h
@@ -12,6 +12,7 @@
 #include <filesystem>
 #include <QMainWindow>
 #include <QMessageBox>
+#include <QFutureWatcher>
 #include <QPushButton>
 #include <QTimer>
 #include <QTranslator>
@@ -19,6 +20,7 @@
 
 #include "common/common_types.h"
 #include "common/settings_enums.h"
+#include "core/file_sys/nup_writer.h"
 #include "frontend_common/content_manager.h"
 #include "input_common/drivers/tas_input.h"
 #include "qt_common/config/qt_config.h"
@@ -352,6 +354,7 @@ private slots:
     void OnGameListSetPlayTime(u64 program_id);
     void OnGameListDumpRomFS(u64 program_id, const std::string& game_path, DumpRomFSTarget target);
     void OnGameListVerifyIntegrity(const std::string& game_path);
+    void OnGameListConvertToNup(const std::string& game_path);
     void OnGameListCopyTID(u64 program_id);
     void OnGameListCreateShortcut(u64 program_id, const std::string& game_path,
                                   const QtCommon::Game::ShortcutTarget target);
@@ -570,6 +573,11 @@ private:
 
     // Install progress dialog
     QProgressDialog* install_progress = nullptr;
+    QProgressDialog* nup_progress = nullptr;
+    QFutureWatcher<FileSys::Nup::PackResult> nup_watcher;
+    std::shared_ptr<std::atomic_bool> nup_cancel;
+    bool nup_running{};
+    std::string nup_source_path;
 
     // Last game booted, used for multi-process apps
     QString last_filename_booted;
diff --git a/src/yuzu_cmd/yuzu.cpp b/src/yuzu_cmd/yuzu.cpp
index 4d71a29993..bc4002d8af 100644
--- a/src/yuzu_cmd/yuzu.cpp
+++ b/src/yuzu_cmd/yuzu.cpp
@@ -12,7 +12,9 @@
 #include <cstdlib>
 #include <chrono>
 #include <cstdio>
+#include <csignal>
 #include <cstring>
+#include <filesystem>
 #include <iostream>
 #include <memory>
 #include <mutex>
@@ -36,6 +38,7 @@
 #include "core/core_timing.h"
 #include "core/cpu_manager.h"
 #include "core/crypto/key_manager.h"
+#include "core/file_sys/nup_writer.h"
 #include "core/file_sys/registered_cache.h"
 #include "core/file_sys/vfs/vfs_real.h"
 #include "core/hle/service/am/applet_manager.h"
@@ -248,6 +251,49 @@ struct SdlState {
     std::unique_ptr<EmuWindow_SDL3> emu_window;
 };
 
+static std::atomic_bool pack_nup_cancel{false};
+
+// eden-cli --pack-nup <dump> [<out.nup>]; the output defaults to <dump>.nup next to the dump.
+static bool PackNup(const std::string& source, const std::string& output) {
+    const auto to_path = [](const std::string& utf8) {
+        return std::filesystem::path{std::u8string{utf8.begin(), utf8.end()}};
+    };
+    const auto dump_root = to_path(source);
+    const auto archive =
+        output.empty() ? FileSys::Nup::DefaultArchivePath(dump_root) : to_path(output);
+    std::signal(SIGINT, [](int) { pack_nup_cancel = true; });
+
+    const auto start = std::chrono::steady_clock::now();
+    auto last_report = start;
+    std::string error;
+    const auto result = FileSys::Nup::PackDump(
+        dump_root, archive, {},
+        [&](const FileSys::Nup::PackProgress& p) {
+            const auto now = std::chrono::steady_clock::now();
+            if (now - last_report < std::chrono::seconds(1) && p.files_done != p.files_total) {
+                return;
+            }
+            last_report = now;
+            fmt::print(stderr, "\r{} / {} MiB, {} / {} files", p.bytes_done >> 20,
+                       p.bytes_total >> 20, p.files_done, p.files_total);
+        },
+        &pack_nup_cancel, &error);
+    const auto seconds =
+        std::chrono::duration<double>(std::chrono::steady_clock::now() - start).count();
+    fmt::print(stderr, "\n");
+    switch (result) {
+    case FileSys::Nup::PackResult::Success:
+        fmt::print(stderr, "Wrote {} in {:.1f} s\n", archive.string(), seconds);
+        return true;
+    case FileSys::Nup::PackResult::Cancelled:
+        fmt::print(stderr, "Cancelled\n");
+        return false;
+    default:
+        fmt::print(stderr, "Packing failed: {}\n", error);
+        return false;
+    }
+}
+
 extern "C" SDL_AppResult SDL_AppInit(void **appstate, int argc, char **argv) {
 #ifdef _WIN32
     SetUnhandledExceptionFilter(WriteCrashDump);
@@ -298,6 +344,10 @@ extern "C" SDL_AppResult SDL_AppInit(void **appstate, int argc, char **argv) {
 
     Core::ApplyLaunchParams(lp);
 
+    if (lp.pack_nup_source) {
+        return PackNup(*lp.pack_nup_source, lp.filepath) ? SDL_APP_SUCCESS : SDL_APP_FAILURE;
+    }
+
     if (lp.filepath.empty()) {
         LOG_CRITICAL(Frontend, "Failed to load ROM: No ROM specified");
         return SDL_APP_FAILURE;