chore: initial project import

backend/fleet/src/Fleet.Rpc/OutboxFrame.cs

@@ -0,0 +1,35 @@
+namespace Fleet.Rpc;
+
+/// <summary>
+/// 发件箱二进制帧：<c>u8 channel | 16 字节 msg_id (UUIDv7) | 正文</c>。
+/// 服务端按 msg_id 去重，持久化之后才回复 <c>fleet.outbox.ack</c>。
+/// </summary>
+public static class OutboxFrame
+{
+    public const int HeaderBytes = 1 + 16;
+
+    public static bool TryParse(ReadOnlyMemory<byte> frame, out byte channel, out Guid msgId, out ReadOnlyMemory<byte> payload)
+    {
+        if (frame.Length < HeaderBytes)
+        {
+            channel = 0;
+            msgId = Guid.Empty;
+            payload = default;
+            return false;
+        }
+
+        channel = frame.Span[0];
+        msgId = new Guid(frame.Span.Slice(1, 16), bigEndian: true);
+        payload = frame[HeaderBytes..];
+        return true;
+    }
+
+    public static byte[] Build(byte channel, Guid msgId, ReadOnlySpan<byte> payload)
+    {
+        byte[] frame = new byte[HeaderBytes + payload.Length];
+        frame[0] = channel;
+        msgId.TryWriteBytes(frame.AsSpan(1, 16), bigEndian: true, out _);
+        payload.CopyTo(frame.AsSpan(HeaderBytes));
+        return frame;
+    }
+}