fix: parse 2.x channel server references with the strict JsonPointer

Removes the lenient JsonPointer.UnescapeToken. The 2.x writer now parses
the reference fragment with JsonPointer, so a name is only written for an
exact /servers/{name} pointer. Nested or malformed pointers (for example
a '~' not followed by '0' or '1') are written unchanged, like other
non-server references.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: bielu

src/ByteBard.AsyncAPI/JsonPointer.cs

@@ -92,16 +92,6 @@ public static string EscapeToken(string token)
             return token.Replace("~", "~0").Replace("/", "~1");
         }
 
-        /// <summary>
-        /// Unescapes a single reference token, so "~1" becomes "/" and "~0" becomes "~".
-        /// Unlike parsing a pointer, this does not reject a "~" that is not part of an escape sequence.
-        /// </summary>
-        /// <param name="token">The escaped token.</param>
-        public static string UnescapeToken(string token)
-        {
-            return token.Replace("~1", "/").Replace("~0", "~");
-        }
-
         /// <summary>
         /// Gets the JSON string representation of this JSON pointer.
         /// </summary>

src/ByteBard.AsyncAPI/Models/AsyncApiChannel.cs

@@ -3,6 +3,7 @@
     using System;
     using System.Collections.Generic;
     using System.Linq;
+    using ByteBard.AsyncAPI.Exceptions;
     using ByteBard.AsyncAPI.Extensions;
     using ByteBard.AsyncAPI.Models.Interfaces;
     using ByteBard.AsyncAPI.Writers;
@@ -173,15 +174,24 @@ private bool CheckOperationChannel(AsyncApiOperation operation, IAsyncApiWriter
         /// </summary>
         private static string GetV2ServerName(AsyncApiServerReference server)
         {
-            const string serversPrefix = "/" + AsyncApiConstants.Servers + "/";
             var reference = server.Reference;
-            if (reference.IsExternal || reference.FragmentId?.StartsWith(serversPrefix) != true)
+            if (reference.IsExternal || reference.FragmentId == null)
             {
                 return reference.Reference;
             }
 
-            // The 2.x reader keeps the name unescaped, while a 3.x pointer escapes it, so decode the whole remainder as one token.
-            return JsonPointer.UnescapeToken(reference.FragmentId.Substring(serversPrefix.Length));
+            string[] tokens;
+            try
+            {
+                tokens = new JsonPointer(reference.FragmentId).Tokens;
+            }
+            catch (AsyncApiException)
+            {
+                // A malformed pointer names no server, so it is kept as is like any other non-server reference.
+                return reference.Reference;
+            }
+
+            return tokens.Length == 2 && tokens[0] == AsyncApiConstants.Servers ? tokens[1] : reference.Reference;
         }
     }
 }

test/ByteBard.AsyncAPI.Tests/Models/AsyncApiChannel_Should.cs

@@ -208,6 +208,9 @@ public void V2_AsyncApiChannel_WithServerReference_SerializesServerName()
         [TestCase("#/servers/a~0b", "a~b")]
         [TestCase("other.yaml#/servers/production", "other.yaml#/servers/production")]
         [TestCase("#/components/servers/production", "'#/components/servers/production'")]
+        [TestCase("#/servers/production/url", "'#/servers/production/url'")]
+        [TestCase("#/servers/a~2b", "'#/servers/a~2b'")]
+        [TestCase("#/servers/a~", "'#/servers/a~'")]
         public void V2_AsyncApiChannel_WithServerReference_SerializesServerNameOnlyForLocalServer(string reference, string expectedServer)
         {
             var channel = new AsyncApiChannel