diff --git a/changelog.d/unreleased/3306-3308.fixed.md b/changelog.d/unreleased/3306-3308.fixed.md
new file mode 100644
index 0000000000..99801f947b
--- /dev/null
+++ b/changelog.d/unreleased/3306-3308.fixed.md
@@ -0,0 +1,17 @@
+---
+category: fixed
+issues:
+  - 3306
+  - 3307
+  - 3308
+affected:
+  - tests/CodeIndex.Tests/McpAuditLogTests.cs
+---
+
+## English
+
+- **MCP audit request-id truncation coverage now uses a protocol-valid escaped id (#3306, #3307, #3308)**: the regression test now keeps the JSON-RPC id within request validation limits while still making the serialized audit request id exceed the audit display cap.
+
+## 日本語
+
+- **MCP audit request-id truncation のカバレッジが protocol-valid な escaped id を使うようになりました (#3306, #3307, #3308)**: 回帰テストは JSON-RPC id を request validation の上限内に保ちつつ、serialized audit request id が audit 表示上限を超える入力で検証するようになりました。
diff --git a/tests/CodeIndex.Tests/McpAuditLogTests.cs b/tests/CodeIndex.Tests/McpAuditLogTests.cs
index 507161074c..94e0ee9ba9 100644
--- a/tests/CodeIndex.Tests/McpAuditLogTests.cs
+++ b/tests/CodeIndex.Tests/McpAuditLogTests.cs
@@ -1,4 +1,5 @@
 using System.Globalization;
+using System.Text;
 using System.Text.Json;
 using System.Text.Json.Nodes;
 using CodeIndex.Cli;
@@ -126,7 +127,7 @@ public void ToolsCall_MissingToolName_StillEmitsAuditRecord()
     }
 
     [Fact]
-    public void ToolsCall_OversizedRequestId_IsRejectedBeforeAuditRecord_Issue3104()
+    public void ToolsCall_OversizedRequestId_IsRejectedBeforeAuditRecord_Issue3104_3308()
     {
         using var sink = new AuditLogSink(_auditPath, AuditLogSink.DefaultMaxBytes, includeValues: false);
         using var server = CreateServer(sink);
@@ -462,12 +463,13 @@ public void ToolsCall_CapsAuditArgumentKeyCount_Issue3237()
     }
 
     [Fact]
-    public void ToolsCall_MaxLengthRequestId_PreservesAuditRequestId_Issue3237()
+    public void ToolsCall_MaxLengthRequestId_PreservesAuditRequestId_Issue3237_3307()
     {
         using var sink = new AuditLogSink(_auditPath, AuditLogSink.DefaultMaxBytes, includeValues: false);
         using var server = CreateServer(sink);
         var id = new string('r', McpServer.MaxRequestIdCharacterCount);
         var serializedId = JsonSerializer.Serialize(id);
+        Assert.True(serializedId.Length <= AuditLogSink.MaxRequestIdChars);
         var request = new JsonObject
         {
             ["jsonrpc"] = "2.0",
@@ -492,6 +494,39 @@ public void ToolsCall_MaxLengthRequestId_PreservesAuditRequestId_Issue3237()
         Assert.False(record.TryGetProperty("request_id_truncated", out _));
     }
 
+    [Fact]
+    public void ToolsCall_EscapedRequestId_TruncatesAuditRequestId_Issue3306()
+    {
+        using var sink = new AuditLogSink(_auditPath, AuditLogSink.DefaultMaxBytes, includeValues: false);
+        using var server = CreateServer(sink);
+        var id = new string('\u3042', 43);
+        Assert.True(id.Length <= McpServer.MaxRequestIdCharacterCount);
+        Assert.True(Encoding.UTF8.GetByteCount(id) <= McpServer.MaxRequestIdByteLength);
+        var serializedId = JsonSerializer.Serialize(id);
+        Assert.True(serializedId.Length > AuditLogSink.MaxRequestIdChars);
+        var requestIdDisplay = McpBoundedText.ForDisplay(serializedId, AuditLogSink.MaxRequestIdChars);
+        var request = new JsonObject
+        {
+            ["jsonrpc"] = "2.0",
+            ["id"] = id,
+            ["method"] = "tools/call",
+            ["params"] = new JsonObject
+            {
+                ["name"] = "ping",
+                ["arguments"] = new JsonObject(),
+            },
+        };
+
+        var response = server.HandleMessage(request)!;
+
+        Assert.False(response.AsObject().ContainsKey("error"));
+        Assert.NotNull(response["result"]);
+        var record = ReadOnlyRecord();
+        Assert.Equal(requestIdDisplay.Text, record.GetProperty("request_id").GetString());
+        Assert.Equal(serializedId.Length, record.GetProperty("request_id_length").GetInt32());
+        Assert.True(record.GetProperty("request_id_truncated").GetBoolean());
+    }
+
     [Fact]
     public void ToolsCall_ValuesOmitted_ByDefault()
     {