diff --git a/dub.json b/dub.json
index d9c5233..90807f2 100644
--- a/dub.json
+++ b/dub.json
@@ -16,5 +16,33 @@
 			"repository": "git+https://git.zhirov.kz/dlang/xdiff.git",
 			"version": "e2396bc172eba813cdcd1a96c494e35d687f576a"
 		}
+	},
+	"configurations": [
+		{
+			"name": "lib",
+			"targetType": "library",
+			"sourcePaths": [
+				"source"
+			],
+			"excludedSourceFiles": [
+				"source/app.d"
+			]
+		},
+		{
+			"name": "app",
+			"targetType": "executable",
+			"mainSourceFile": "source/app.d",
+			"sourcePaths": [
+				"source"
+			]
+		}
+	],
+	"buildTypes": {
+		"unittest": {
+			"dflags": [
+				"-unittest",
+				"-g"
+			]
+		}
 	}
 }
\ No newline at end of file
diff --git a/dub.selections.json b/dub.selections.json
new file mode 100644
index 0000000..0b7884b
--- /dev/null
+++ b/dub.selections.json
@@ -0,0 +1,6 @@
+{
+	"fileVersion": 1,
+	"versions": {
+		"xdiff": {"version":"e2396bc172eba813cdcd1a96c494e35d687f576a","repository":"git+https://git.zhirov.kz/dlang/xdiff.git"}
+	}
+}
diff --git a/source/app.d b/source/app.d
index 30e9f34..aaec5e6 100644
--- a/source/app.d
+++ b/source/app.d
@@ -1,25 +1,16 @@
-import std.stdio : writeln, stderr;
-import std.exception : collectException;
+import std.stdio;
+import xdiff_mmfile : MMFile;
 
-import diff;
-
-int main(string[] args)
+void main()
 {
-	if (args.length != 3)
-	{
-		stderr.writeln("use: ", args[0], " OLD NEW");
-		return 1;
-	}
+    auto a = MMFile.fromBytes(cast(ubyte[])"hello world\n");
+    auto b = MMFile.fromBytes(cast(ubyte[])"hello world!\n");
 
-	auto eng = new DiffEngine(3);
+    auto patch = a.computePatch(b);
+    writeln("patch size: ", patch.size());
 
-	string result; // сюда положим результат
-	auto ex = collectException(result = eng.diffFiles(args[1], args[2]));
-	if (ex !is null)
-	{
-		stderr.writeln(ex.msg);
-		return 2;
-	}
-	writeln(result);
-	return 0;
+    auto res = a.applyPatch(patch);
+    writeln("apply success: ", res.success);
+    write(res.patched.asSlice()); // печатаем результат
+    writeln();
 }
diff --git a/source/diff.d b/source/diff.d
deleted file mode 100644
index d3b1310..0000000
--- a/source/diff.d
+++ /dev/null
@@ -1,197 +0,0 @@
-module diff;
-
-import std.exception : enforce;
-import std.file : read, exists; // бинарное чтение
-import std.array : Appender, appender;
-import std.string : representation, format;
-import std.datetime : Clock, UTC;
-
-import core.stdc.string : memcpy;
-import core.stdc.stdlib : malloc, free, realloc;
-
-import xdiff;
-
-//-----------------------------
-// Аллокатор для libxdiff (обязателен на ряде сборок)
-//-----------------------------
-private extern (C) void* _wrap_malloc(void*, uint size)
-{
-	return malloc(size);
-}
-
-private extern (C) void _wrap_free(void*, void* ptr)
-{
-	free(ptr);
-}
-
-private extern (C) void* _wrap_realloc(void*, void* ptr, uint size)
-{
-	return realloc(ptr, size);
-}
-
-private __gshared bool _allocatorReady = false;
-
-private void ensureAllocator()
-{
-	if (_allocatorReady)
-		return;
-	memallocator_t malt;
-	malt.priv = null;
-	malt.malloc = &_wrap_malloc;
-	malt.free = &_wrap_free;
-	malt.realloc = &_wrap_realloc;
-	enforce(xdl_set_allocator(&malt) == 0, "xdl_set_allocator failed");
-	_allocatorReady = true;
-}
-
-//-----------------------------
-// RAII для mmfile_t
-//-----------------------------
-private struct MmFile
-{
-	mmfile_t mf;
-
-	static MmFile fromBytes(const(ubyte)[] data,
-		long bsize = 8 * 1024,
-		ulong flags = XDL_MMF_ATOMIC)
-	{
-		ensureAllocator(); // критично: до init/writeallocate
-		MmFile m;
-		enforce(xdl_init_mmfile(&m.mf, bsize, flags) == 0, "xdl_init_mmfile failed");
-
-		if (data.length)
-		{
-			auto dst = cast(char*) xdl_mmfile_writeallocate(&m.mf, data.length);
-			enforce(dst !is null, "xdl_mmfile_writeallocate failed");
-			memcpy(dst, data.ptr, data.length);
-		}
-		return m;
-	}
-
-	~this()
-	{
-		xdl_free_mmfile(&mf);
-	}
-}
-
-//-----------------------------
-// Синк-коллектор вывода libxdiff
-//-----------------------------
-private class BufferSink
-{
-	Appender!(ubyte[]) outbuf;
-
-	this()
-	{
-		outbuf = appender!(ubyte[])();
-	}
-
-	extern (C) static int writeCB(void* priv, mmbuffer_t* mb, int nbuf)
-	{
-		auto self = cast(BufferSink) priv;
-		foreach (i; 0 .. nbuf)
-		{
-			size_t sz = cast(size_t) mb[i].size;
-			if (sz == 0)
-				continue;
-			self.outbuf.put((cast(ubyte*) mb[i].ptr)[0 .. sz]);
-		}
-		return 0;
-	}
-
-	string toStringOwned() @trusted
-	{
-		return cast(string) outbuf.data.idup;
-	}
-}
-
-//-----------------------------
-// Публичный движок unified-diff
-//-----------------------------
-final class DiffEngine
-{
-	private long _ctxlen;
-	private bool _stripTrailingNewline;
-
-	this(long ctxlen = 3, bool stripTrailingNewline = false)
-	{
-		_ctxlen = ctxlen;
-		_stripTrailingNewline = stripTrailingNewline;
-	}
-
-	/// Diff двух текстов (UTF-8 строки)
-	string diffText(string oldText, string newText,
-		string oldLabel = "old", string newLabel = "new")
-	{
-		const(ubyte)[] a = _prep(oldText);
-		const(ubyte)[] b = _prep(newText);
-		return diffBytes(a, b, oldLabel, newLabel);
-	}
-
-	/// Diff по путям (файлы читаются целиком, бинарно)
-	string diffFiles(string oldPath, string newPath,
-		string oldLabel = "", string newLabel = "")
-	{
-		enforce(exists(oldPath), "no such file: " ~ oldPath);
-		enforce(exists(newPath), "no such file: " ~ newPath);
-
-		auto a = cast(const(ubyte)[]) read(oldPath); // бинарное чтение
-		auto b = cast(const(ubyte)[]) read(newPath);
-
-		if (oldLabel.length == 0)
-			oldLabel = oldPath;
-		if (newLabel.length == 0)
-			newLabel = newPath;
-
-		return diffBytes(a, b, oldLabel, newLabel);
-	}
-
-	/// Базовый метод: diff двух буферов
-	string diffBytes(const(ubyte)[] oldBytes, const(ubyte)[] newBytes,
-		string oldLabel = "old", string newLabel = "new")
-	{
-		auto a = MmFile.fromBytes(oldBytes);
-		auto b = MmFile.fromBytes(newBytes);
-
-		auto sink = new BufferSink;
-		xdemitcb_t ecb;
-		ecb.priv = cast(void*) sink;
-		ecb.outf = &BufferSink.writeCB;
-
-		xpparam_t xpp;
-		xpp.flags = 0;
-
-		xdemitconf_t xecfg;
-		xecfg.ctxlen = _ctxlen;
-
-		auto pre = formatHeaders(oldLabel, newLabel);
-
-		auto rc = xdl_diff(&a.mf, &b.mf, &xpp, &xecfg, &ecb);
-		enforce(rc >= 0, format("xdl_diff failed (rc=%s)", rc));
-
-		return pre ~ sink.toStringOwned();
-	}
-
-	static string formatHeaders(string oldLabel, string newLabel)
-	{
-		auto ts = Clock.currTime(UTC()).toISOExtString(); // YYYY-MM-DDTHH:MM:SS
-		return "--- " ~ oldLabel ~ "\t" ~ ts ~ "\n"
-			~ "+++ " ~ newLabel ~ "\t" ~ ts ~ "\n";
-	}
-
-private:
-	const(ubyte)[] _prep(string s) @trusted
-	{
-		auto bytes = cast(const(ubyte)[]) s.representation;
-		if (_stripTrailingNewline && (bytes.length && bytes[$ - 1] != '\n'))
-		{
-			ubyte[] tmp;
-			tmp.length = bytes.length + 1;
-			if (bytes.length)
-				memcpy(tmp.ptr, bytes.ptr, bytes.length);
-			tmp[$ - 1] = cast(ubyte) '\n';
-			return cast(const(ubyte)[]) tmp;
-		}
-		return bytes;
-	}
-}
diff --git a/source/xdiff_init.d b/source/xdiff_init.d
new file mode 100644
index 0000000..d73cc09
--- /dev/null
+++ b/source/xdiff_init.d
@@ -0,0 +1,33 @@
+module xdiff_init;
+
+import core.stdc.stdlib : malloc, free, realloc;
+import std.exception : enforce;
+import xdiff; // твой низкоуровневый биндинг (xdiff.d)
+
+extern (C) private void* wrap_malloc(void*, uint size) { return malloc(size); }
+extern (C) private void  wrap_free  (void*, void* p)   { free(p); }
+extern (C) private void* wrap_realloc(void*, void* p, uint size){ return realloc(p, size); }
+
+void ensureInit()
+{
+    // локальная статика инициализируется один раз на процесс
+    static bool done = false;
+    if (done) return;
+
+    memallocator_t m;
+    m.priv = null;
+    m.malloc = &wrap_malloc;
+    m.free = &wrap_free;
+    m.realloc = &wrap_realloc;
+
+    enforce(xdl_set_allocator(&m) == 0, "xdl_set_allocator failed");
+    done = true;
+}
+
+mmfile_t initMmfile(size_t len)
+{
+    ensureInit();
+    mmfile_t mf;
+    enforce(xdl_init_mmfile(&mf, cast(long)len, XDL_MMF_ATOMIC) == 0, "xdl_init_mmfile failed");
+    return mf;
+}
diff --git a/source/xdiff_mmblocks.d b/source/xdiff_mmblocks.d
new file mode 100644
index 0000000..81eeec0
--- /dev/null
+++ b/source/xdiff_mmblocks.d
@@ -0,0 +1,108 @@
+module xdiff_mmblocks;
+
+import std.exception : enforce;
+import xdiff_init : ensureInit, initMmfile;
+import xdiff;
+
+final class MMBlocks
+{
+private:
+    mmfile_t _inner;
+    bool     _owned = true;        // владеем ли блоками?
+    enum DEFAULT_BSIZE = 8 * 1024;
+
+    // Глубокая копия: читаем все блоки и записываем в dst
+    static void deepCopyAll(mmfile_t* src, MMBlocks dst)
+    {
+        enforce(xdl_seek_mmfile(src, 0) == 0, "seek(0) failed");
+
+        long sz = 0;
+        auto p  = xdl_mmfile_first(src, &sz);
+        while (p !is null && sz > 0)
+        {
+            auto wrote = xdl_write_mmfile(dst.mmfilePtr(), p, sz);
+            enforce(wrote == sz, "write failed during deep copy");
+            p = xdl_mmfile_next(src, &sz);
+        }
+    }
+
+public:
+    this()
+    {
+        _inner = initMmfile(DEFAULT_BSIZE);
+    }
+
+    static MMBlocks fromBytes(const(ubyte)[] data)
+    {
+        auto b = new MMBlocks;
+        if (data.length > 0)
+        {
+            auto wrote = xdl_write_mmfile(&b._inner, data.ptr, cast(long)data.length);
+            enforce(wrote == cast(long)data.length, "xdl_write_mmfile wrote less than requested");
+        }
+        return b;
+    }
+
+    ~this()
+    {
+        if (_owned && _inner.head !is null)
+            xdl_free_mmfile(&_inner);
+
+        // обнулим на всякий случай
+        _inner.head = null; _inner.tail = null;
+        _inner.rcur = null; _inner.wcur = null;
+        _inner.fsize = 0;   _inner.bsize = 0;
+    }
+
+    // доступ к внутреннему mmfile_t*
+    mmfile_t* mmfilePtr() @trusted { return &_inner; }
+
+    size_t size()            { return cast(size_t)xdl_mmfile_size(&_inner); }
+    bool   isCompact() const { return xdl_mmfile_iscompact(cast(mmfile_t*)&_inner) != 0; }
+
+    int writeBuf(const(ubyte)[] buf)
+    {
+        auto wrote = xdl_write_mmfile(&_inner, buf.ptr, cast(long)buf.length);
+        return (wrote == cast(long)buf.length) ? 0 : -1;
+    }
+
+    /// Глубокая копия (новое владение)
+    MMBlocks clone() const
+    {
+        auto dst = new MMBlocks;
+        // deepCopyAll принимает mmfile_t*, поэтому аккуратно снимаем const с заголовка:
+        deepCopyAll(cast(mmfile_t*)&_inner, dst);
+        return dst;
+    }
+
+    /// Компактизация через пересборку содержимого
+    void toCompact()
+    {
+        if (isCompact()) return;
+
+        auto dst = new MMBlocks;
+        deepCopyAll(&_inner, dst);
+
+        // перехватываем владение содержимым dst
+        if (_owned && _inner.head !is null)
+            xdl_free_mmfile(&_inner);
+
+        _inner = *dst.mmfilePtr();
+        dst._owned = false;           // dst больше не владеет
+        dst._inner.head = null;       // чтобы финалайзер dst ничего не освободил
+        dst._inner.tail = null;
+        dst._inner.rcur = null;
+        dst._inner.wcur = null;
+        dst._inner.fsize = 0;
+        dst._inner.bsize = 0;
+    }
+
+    /// Снять владение (используется при move в MMFile)
+    void disarm()
+    {
+        _owned = false;
+        _inner.head = null; _inner.tail = null;
+        _inner.rcur = null; _inner.wcur = null;
+        _inner.fsize = 0;   _inner.bsize = 0;
+    }
+}
diff --git a/source/xdiff_mmfile.d b/source/xdiff_mmfile.d
new file mode 100644
index 0000000..bbd5251
--- /dev/null
+++ b/source/xdiff_mmfile.d
@@ -0,0 +1,166 @@
+module xdiff_mmfile;
+
+import std.exception : enforce;
+import xdiff_init : ensureInit, initMmfile;
+import xdiff_mmblocks : MMBlocks;
+import xdiff;
+
+final class MMFile
+{
+private:
+    mmfile_t _inner;
+    bool     _owned = true;
+
+public:
+    this()
+    {
+        _inner = initMmfile(0);
+    }
+
+    static MMFile fromBytes(const(ubyte)[] data)
+    {
+        auto f = new MMFile;
+        if (data.length > 0)
+        {
+            auto wrote = xdl_write_mmfile(&f._inner, data.ptr, cast(long)data.length);
+            enforce(wrote == cast(long)data.length, "xdl_write_mmfile wrote less than requested");
+        }
+        return f;
+    }
+
+    ~this()
+    {
+        if (_owned && _inner.head !is null)
+            xdl_free_mmfile(&_inner);
+
+        _inner.head = null; _inner.tail = null;
+        _inner.rcur = null; _inner.wcur = null;
+        _inner.fsize = 0;   _inner.bsize = 0;
+    }
+
+    size_t size()            { return cast(size_t)xdl_mmfile_size(&_inner); }
+    bool   isCompact() const { return xdl_mmfile_iscompact(cast(mmfile_t*)&_inner) != 0; }
+
+    const(ubyte)[] asSlice() const
+    {
+        enforce(isCompact(), "MMFile must be compact for asSlice");
+        auto h = _inner.head;
+        if (h is null || h.size <= 0) return (cast(ubyte*)null)[0 .. 0];
+        return (cast(const(ubyte)*)h.ptr)[0 .. cast(size_t)h.size];
+    }
+
+    ubyte[] asSliceMut()
+    {
+        enforce(isCompact(), "MMFile must be compact for asSliceMut");
+        auto h = _inner.head;
+        if (h is null || h.size <= 0) return (cast(ubyte*)null)[0 .. 0];
+        return (cast(ubyte*)h.ptr)[0 .. cast(size_t)h.size];
+    }
+
+    alias MMPatch = MMBlocks;
+
+    /// Сформировать patch (diff self → other)
+    MMPatch computePatch(ref MMFile other)
+    {
+        auto patch = new MMBlocks();
+
+        static extern(C) int emitToPatch(void* priv, mmbuffer_t* bufs, int num)
+        {
+            auto target = cast(MMBlocks)priv; // класс
+            foreach (i; 0 .. num)
+            {
+                auto b = bufs + i;
+                auto wrote = xdl_writem_mmfile(target.mmfilePtr(), b, 1);
+                if (wrote != (*b).size) return -1;
+            }
+            return 0;
+        }
+
+        xpparam_t xpp; xpp.flags = 0;
+        xdemitconf_t xec; xec.ctxlen = 3;
+        xdemitcb_t ecb; ecb.priv = cast(void*)patch; ecb.outf = &emitToPatch;
+
+        auto rc = xdl_diff(&_inner, &other._inner, &xpp, &xec, &ecb);
+        enforce(rc == 0, "xdl_diff failed");
+        return patch;
+    }
+
+    struct PatchResult { bool success; MMFile patched; MMFile rejected; }
+
+    /// Применить patch к self
+    PatchResult applyPatch(ref MMPatch patch)
+    {
+        patch.toCompact();
+
+        auto acc = new MMBlocks();
+        auto rej = new MMBlocks();
+
+        static extern(C) int emitTo(void* priv, mmbuffer_t* bufs, int num)
+        {
+            auto target = cast(MMBlocks)priv; // класс
+            long expect = 0; foreach (i; 0 .. num) expect += (bufs + i).size;
+            auto wrote = xdl_writem_mmfile(target.mmfilePtr(), bufs, num);
+            return (wrote == expect) ? 0 : -1;
+        }
+
+        xdemitcb_t accCb; accCb.priv = cast(void*)acc; accCb.outf = &emitTo;
+        xdemitcb_t rejCb; rejCb.priv = cast(void*)rej; rejCb.outf = &emitTo;
+
+        auto rc = xdl_patch(&_inner, patch.mmfilePtr(), XDL_PATCH_NORMAL, &accCb, &rejCb);
+        enforce(rc == 0 || rc == 1, "xdl_patch failed");
+
+        auto accFile = MMFile.fromBlocksMoved(acc);
+        auto rejFile = MMFile.fromBlocksMoved(rej);
+
+        bool ok = (rejFile.size() == 0);
+        return PatchResult(ok, accFile, rejFile);
+    }
+
+    /// 3-way merge: коллбэки nothrow, чтобы не бросать через C
+    void merge3Raw(
+        ref MMFile f1,
+        ref MMFile f2,
+        scope int delegate(const(ubyte)[]) nothrow acceptCb,
+        scope int delegate(const(ubyte)[]) nothrow rejectCb)
+    {
+        static extern(C) int emitAccept(void* priv, mmbuffer_t* bufs, int num)
+        {
+            auto d = cast(int delegate(const(ubyte)[]) nothrow*)priv;
+            foreach (i; 0 .. num)
+            {
+                auto b = bufs + i;
+                auto slice = (cast(const(ubyte)*)((*b).ptr))[0 .. cast(size_t)((*b).size)];
+                auto r = (*d)(slice); if (r != 0) return r;
+            }
+            return 0;
+        }
+        static extern(C) int emitReject(void* priv, mmbuffer_t* bufs, int num)
+        {
+            auto d = cast(int delegate(const(ubyte)[]) nothrow*)priv;
+            foreach (i; 0 .. num)
+            {
+                auto b = bufs + i;
+                auto slice = (cast(const(ubyte)*)((*b).ptr))[0 .. cast(size_t)((*b).size)];
+                auto r = (*d)(slice); if (r != 0) return r;
+            }
+            return 0;
+        }
+
+        auto a = acceptCb, r = rejectCb;
+        xdemitcb_t accCb; accCb.priv = cast(void*)&a; accCb.outf = &emitAccept;
+        xdemitcb_t rejCb; rejCb.priv = cast(void*)&r; rejCb.outf = &emitReject;
+
+        auto rc = xdl_merge3(&_inner, &f1._inner, &f2._inner, &accCb, &rejCb);
+        enforce(rc == 0, "xdl_merge3 failed");
+    }
+
+    /// «Move» из MMBlocks: забрать владение внутренними блоками
+    static MMFile fromBlocksMoved(MMBlocks b)
+    {
+        b.toCompact();
+        auto f = new MMFile;
+        f._inner = *b.mmfilePtr(); // копируем заголовок (указатели на блоки)
+        b.disarm();                // источник больше не владеет
+        return f;
+    }
+}
diff --git a/source/xdiff_unittests.d b/source/xdiff_unittests.d
new file mode 100644
index 0000000..8646f42
--- /dev/null
+++ b/source/xdiff_unittests.d
@@ -0,0 +1,246 @@
+module xdiff_unittests;
+
+import std.algorithm : equal;
+import std.array : appender;
+import std.exception : assertThrown;
+import std.range : iota, cycle, take;
+import xdiff_mmfile : MMFile;
+import xdiff_mmblocks : MMBlocks;
+
+// -------------------- Вспомогалки --------------------
+
+/// Сгенерировать массив длиной n, цикляя значения 0..239
+ubyte[] genCycled(size_t n)
+{
+    auto acc = appender!(ubyte[])();
+    foreach (v; iota(0, 240).cycle.take(n))
+        acc.put(cast(ubyte)v);
+    return acc.data;
+}
+
+/// Вытянуть контент MMBlocks в байты (не разрушая оригинал)
+ubyte[] blocksToBytes(const MMBlocks b)
+{
+    auto tmp = b.clone();                // глубокая копия
+    auto mf  = MMFile.fromBlocksMoved(tmp);
+    return (cast(const(ubyte)[]) mf.asSlice()).dup;
+}
+
+/// Сравнить содержимое двух MMFile по байтам
+bool sameBytes(const MMFile a, const MMFile b)
+{
+    return a.asSlice().equal(b.asSlice());
+}
+
+// -------------------- ТЕСТЫ --------------------
+
+unittest // new_empty
+{
+    auto f = new MMFile;
+    assert(f.size() == 0);
+    assert(f.isCompact());
+}
+
+unittest // new_from_bytes
+{
+    auto data = cast(ubyte[])"hello world";
+    auto f = MMFile.fromBytes(data);
+    assert(f.size() == data.length);
+    assert(f.isCompact());
+    assert(f.asSlice().equal(data));
+}
+
+unittest // large_from_bytes
+{
+    auto data = genCycled(15_000);
+    auto f = MMFile.fromBytes(data);
+    assert(f.size() == data.length);
+    assert(f.isCompact());
+    assert(f.asSlice().equal(data));
+}
+
+unittest // "clone" для MMFile: через байты
+{
+    auto data = genCycled(15_000);
+    auto f  = MMFile.fromBytes(data);
+    auto f2 = MMFile.fromBytes(f.asSlice().dup);
+    assert(sameBytes(f, f2));
+}
+
+unittest // clone_blocks
+{
+    auto data = genCycled(15_000);
+    auto b  = MMBlocks.fromBytes(data);
+    auto b2 = b.clone(); // глубокий
+    auto bytes  = blocksToBytes(b);
+    auto bytes2 = blocksToBytes(b2);
+    assert(bytes.equal(bytes2));
+}
+
+unittest // eq для MMFile (по байтам)
+{
+    auto data = genCycled(15_000);
+    auto f  = MMFile.fromBytes(data);
+    auto f2 = MMFile.fromBytes(data.dup);
+    assert(sameBytes(f, f2));
+}
+
+unittest // as_slice
+{
+    assert((new MMFile).asSlice().length == 0);
+
+    auto data = genCycled(15_000);
+    auto f = MMFile.fromBytes(data);
+    assert(f.asSlice().equal(data));
+}
+
+unittest // as_slice_mut
+{
+    auto empty = new MMFile;
+    assert(empty.asSlice().length == 0);
+
+    auto data = genCycled(15_000);
+    auto f = MMFile.fromBytes(data);
+    assert(f.asSlice()[0] == data[0]);
+
+    auto mut = f.asSliceMut();
+    mut[0] = cast(ubyte) (mut[0] + 1);
+    assert(f.asSlice()[0] == data[0] + 1);
+}
+
+unittest // diff_simple → проверяем applyPatch
+{
+    auto data  = cast(ubyte[])"hello world\n";
+    auto data2 = cast(ubyte[])"hello world!\n";
+    auto f  = MMFile.fromBytes(data);
+    auto f2 = MMFile.fromBytes(data2);
+
+    auto patch = f.computePatch(f2);
+    auto r = f.applyPatch(patch);
+    assert(r.success);
+    assert(r.patched.asSlice().equal(data2));
+    assert(r.rejected.asSlice().length == 0);
+}
+
+unittest // diff_with_mutation
+{
+    auto f  = MMFile.fromBytes(cast(ubyte[])"hello world\n");
+    auto f2 = MMFile.fromBytes(cast(ubyte[])"hello world!\n");
+
+    // 1-й прогон
+    auto p1 = f.computePatch(f2);
+    auto r1 = f.applyPatch(p1);
+    assert(r1.success);
+    assert(r1.patched.asSlice().equal(f2.asSlice()));
+
+    // Меняем первую букву во втором файле
+    auto m = f2.asSliceMut();
+    m[0] = cast(ubyte)'j';
+
+    // 2-й прогон
+    auto p2 = f.computePatch(f2);
+    auto r2 = f.applyPatch(p2);
+    assert(r2.success);
+    assert(r2.patched.asSlice().equal(f2.asSlice()));
+}
+
+unittest // merge3_simple (без конфликтов)
+{
+    auto base = MMFile.fromBytes(cast(ubyte[])"header\nline2\nline3\nline4\nhello world\n");
+    auto a    = MMFile.fromBytes(cast(ubyte[])"header\nline2\nline3\nline4\nhello world changed\n");
+    auto b    = MMFile.fromBytes(cast(ubyte[])"header_changed\nline2\nline3\nline4\nhello world\n");
+
+    auto lines = appender!(string[])();
+    auto rej   = appender!(string[])();
+
+    int acceptCb(const(ubyte)[] s) nothrow
+    {
+        lines.put(cast(string) s.idup);
+        return 0;
+    }
+    int rejectCb(const(ubyte)[] s) nothrow
+    {
+        rej.put(cast(string) s.idup);
+        return 0;
+    }
+
+    base.merge3Raw(a, b, &acceptCb, &rejectCb);
+
+    auto expected = [
+        "header_changed\n",
+        "line2\n",
+        "line3\n",
+        "line4\n",
+        "hello world changed\n",
+    ];
+    assert(lines.data.equal(expected));
+    assert(rej.data.length == 0);
+}
+
+unittest // merge3_conflicts (есть rejected)
+{
+    auto base = MMFile.fromBytes(cast(ubyte[])"header\nline2\nline3\nline4\nhello world\n");
+    auto a    = MMFile.fromBytes(cast(ubyte[])"header\nline2\nline3\nline4\nhello world changed\n");
+    auto b    = MMFile.fromBytes(cast(ubyte[])"header\nline2\nline3\nline4\nhello world also changed\n");
+
+    auto lines = appender!(string[])();
+    auto rej   = appender!(string[])();
+
+    int acceptCb(const(ubyte)[] s) nothrow { lines.put(cast(string)s.idup); return 0; }
+    int rejectCb(const(ubyte)[] s) nothrow { rej.put(cast(string)s.idup);   return 0; }
+
+    base.merge3Raw(a, b, &acceptCb, &rejectCb);
+
+    assert(lines.data.length > 0);
+    assert(rej.data.length > 0);
+}
+
+unittest // merge3_panic_* в Rust → у нас error-ветка через nothrow-коды: вернём -1
+{
+    auto base = MMFile.fromBytes(cast(ubyte[])"header\nline2\nline3\nline4\nhello world\n");
+    auto a    = MMFile.fromBytes(cast(ubyte[])"header\nline2\nline3\nline4\nhello world changed\n");
+    auto b    = MMFile.fromBytes(cast(ubyte[])"header_changed\nline2\nline3\nline4\nhello world\n");
+
+    auto lines = appender!(string[])();
+
+    int acceptCb(const(ubyte)[] s) nothrow
+    {
+        static size_t cnt = 0;
+        ++cnt;
+        if (cnt > 3) return -1; // сигнализируем об ошибке
+        lines.put(cast(string)s.idup);
+        return 0;
+    }
+    int rejectCb(const(ubyte)[] s) nothrow { return 0; }
+
+    assertThrown!Exception( base.merge3Raw(a, b, &acceptCb, &rejectCb) );
+}
+
+unittest // patch_simple (computePatch→applyPatch)
+{
+    auto base  = MMFile.fromBytes(cast(ubyte[])"header\nline2\nline3\nline4\nhello world\n");
+    auto want  = MMFile.fromBytes(cast(ubyte[])"header\nline2\nline3\nline4\nhello world changed\n");
+
+    auto patch = base.computePatch(want);
+    auto res   = base.applyPatch(patch);
+
+    assert(res.success);
+    assert(sameBytes(res.patched, want));
+    assert(res.rejected.asSlice().length == 0);
+}
+
+unittest // patch_reject (искажаем базу перед apply)
+{
+    auto base  = MMFile.fromBytes(cast(ubyte[])"header\nline2\nline3\nline4\nhello world\n");
+    auto want  = MMFile.fromBytes(cast(ubyte[])"header changed\nline2\nline3\nline4\nhello world changed\n");
+
+    auto patch = base.computePatch(want);
+
+    auto m = base.asSliceMut();
+    m[0] = cast(ubyte)'b';
+
+    auto res = base.applyPatch(patch);
+
+    assert(!res.success);
+    assert(res.rejected.asSlice().length > 0);
+}