Update wire protocol to version 7 and enhance presence management features

- Bumped the wire protocol version to 7, reflecting significant changes in the communication structure.
- Introduced a new presence message type for real-time occupancy updates, including node activity and individual presence states.
- Updated the API to include a directory endpoint for fetching short id→name mappings, improving client-side name resolution.
- Revised the map snapshot structure to be static, with people and current lessons now handled through the presence stream.
- Enhanced client-side handling of presence updates, including UI adjustments to display live occupancy and activity.
- Updated documentation to reflect the new protocol features and changes in presence management.
- Added tests to validate the new presence functionalities and ensure robust handling of real-time data.

tests/HSchool.Protocol.Tests/ProtocolCodecTests.cs

@@ -85,6 +85,17 @@ public class ProtocolCodecTests
         Assert.Equal(message, ProtocolCodec.ReadSetSpeed(buffer[..length]));
     }
 
+    [Fact]
+    public void SkipEmpty_IsASingleByte()
+    {
+        Span<byte> buffer = stackalloc byte[ProtocolCodec.MaxFrameSize];
+
+        var length = ProtocolCodec.WriteSkipEmpty(buffer);
+
+        Assert.Equal(1, length);
+        Assert.Equal(MessageType.ClientSkipEmpty, ProtocolCodec.PeekMessageType(buffer[..length]));
+    }
+
     [Fact]
     public void Welcome_RoundTripsAndIsFourBytes()
     {
@@ -110,17 +121,44 @@ public class ProtocolCodecTests
     }
 
     [Fact]
-    public void Clock_RoundTripsAndIsFifteenBytes()
+    public void Clock_RoundTripsAndIsTwentyFourBytes()
     {
-        var message = new ServerClockMessage(7, 1_333_432_800_000, Running: true, SpeedIndex: 2);
+        var message = new ServerClockMessage(
+            7,
+            1_333_432_800_000,
+            Running: true,
+            SpeedIndex: 2,
+            SkipAllowed: true,
+            SkipTargetUnixMs: 1_333_516_800_000);
         Span<byte> buffer = stackalloc byte[ProtocolCodec.MaxFrameSize];
 
         var length = ProtocolCodec.WriteClock(buffer, message);
 
-        Assert.Equal(15, length);
+        Assert.Equal(24, length);
+        Assert.Equal((byte)MessageType.ServerClock, buffer[0]);
+        Assert.Equal(7, BitConverter.ToInt32(buffer[1..5]));
+        Assert.Equal(1_333_432_800_000, BitConverter.ToInt64(buffer[5..13]));
+        Assert.Equal(1, buffer[13]);
+        Assert.Equal(2, buffer[14]);
+        Assert.Equal(1, buffer[15]);
+        Assert.Equal(1_333_516_800_000, BitConverter.ToInt64(buffer[16..24]));
         Assert.Equal(message, ProtocolCodec.ReadClock(buffer[..length]));
     }
 
+    [Fact]
+    public void Clock_WithoutSkip_WritesZeroTarget()
+    {
+        var message = new ServerClockMessage(1, 0, Running: false, SpeedIndex: 1);
+        Span<byte> buffer = stackalloc byte[ProtocolCodec.MaxFrameSize];
+
+        var length = ProtocolCodec.WriteClock(buffer, message);
+        var read = ProtocolCodec.ReadClock(buffer[..length]);
+
+        Assert.Equal(24, length);
+        Assert.False(read.SkipAllowed);
+        Assert.Equal(0, read.SkipTargetUnixMs);
+    }
+
     [Fact]
     public void SchoolGone_RoundTripsAndIsFiveBytes()
     {
@@ -164,34 +202,45 @@ public class ProtocolCodecTests
         Assert.Equal(0, read.Nodes[0].PupilSlots);
         Assert.Equal([new MapSnapshotItem("Стул", 2)], read.Nodes[1].Items);
         Assert.Equal(["Директор"], read.Nodes[1].Positions);
-        Assert.Equal("", read.Nodes[0].ActivitySubject);
-        Assert.Empty(read.Nodes[0].Present);
     }
 
     [Fact]
-    public void MapSnapshot_RoundTripsOccupancyAfterPositions()
+    public void Presence_RoundTripsAndWritesHeaderOffsets()
     {
-        var message = new ServerMapSnapshotMessage(3, [
-            new MapSnapshotNode(
-                3,
-                "classroom-101",
-                "floor-1",
-                "Класс 101",
-                16,
-                [new MapSnapshotItem("Парта", 16)],
-                [],
-                "Математика",
-                "5А",
-                ["Иванова Ольга Михайловна", "Соколов Иван Петрович"]),
-        ]);
-        var buffer = new byte[ProtocolCodec.MapSnapshotSize(message)];
+        var message = new ServerPresenceMessage(
+            7,
+            [
+                new PresenceNode("classroom-101", 18, "Математика", "5А"),
+                new PresenceNode("corridor-1", 4),
+            ],
+            [
+                new PresencePerson("f0.c0", "classroom-101", PresenceState.Here),
+                new PresencePerson("f3.p1", "corridor-1", PresenceState.Walking),
+            ]);
+        var buffer = new byte[ProtocolCodec.PresenceSize(message)];
 
-        var length = ProtocolCodec.WriteMapSnapshot(buffer, message);
-        var read = ProtocolCodec.ReadMapSnapshot(buffer.AsSpan(0, length));
+        var length = ProtocolCodec.WritePresence(buffer, message);
 
+        Assert.Equal((byte)MessageType.ServerPresence, buffer[0]);
+        Assert.Equal(7, BitConverter.ToInt32(buffer.AsSpan(1, 4)));
+        Assert.Equal((ushort)2, BitConverter.ToUInt16(buffer.AsSpan(5, 2)));
+        Assert.Equal(length, ProtocolCodec.PresenceSize(message));
+
+        var read = ProtocolCodec.ReadPresence(buffer.AsSpan(0, length));
+        Assert.Equal(message.SchoolId, read.SchoolId);
+        Assert.Equal(2, read.Nodes.Count);
+        Assert.Equal("classroom-101", read.Nodes[0].Id);
+        Assert.Equal(18, read.Nodes[0].Count);
         Assert.Equal("Математика", read.Nodes[0].ActivitySubject);
         Assert.Equal("5А", read.Nodes[0].ActivityClass);
-        Assert.Equal(["Иванова Ольга Михайловна", "Соколов Иван Петрович"], read.Nodes[0].Present);
+        Assert.Equal("corridor-1", read.Nodes[1].Id);
+        Assert.Equal(4, read.Nodes[1].Count);
+        Assert.Equal("", read.Nodes[1].ActivitySubject);
+        Assert.Equal(2, read.People.Count);
+        Assert.Equal("f0.c0", read.People[0].Id);
+        Assert.Equal("classroom-101", read.People[0].NodeId);
+        Assert.Equal(PresenceState.Here, read.People[0].State);
+        Assert.Equal(PresenceState.Walking, read.People[1].State);
     }
 
     [Fact]
@@ -287,7 +336,9 @@ public class ProtocolCodecTests
     {
         // Handlers size clock/welcome/pong buffers from this constant; map snapshots use MaxMessageSize.
         Span<byte> buffer = stackalloc byte[ProtocolCodec.MaxFrameSize];
-        var clock = ProtocolCodec.WriteClock(buffer, new ServerClockMessage(1, long.MaxValue, true, 4));
+        var clock = ProtocolCodec.WriteClock(
+            buffer,
+            new ServerClockMessage(1, long.MaxValue, true, 4, SkipAllowed: true, SkipTargetUnixMs: long.MaxValue));
 
         Assert.True(clock <= ProtocolCodec.MaxFrameSize);
     }