feat: support long text and safe attachment batches

tests/node-agent/WxAgent.Core.Tests/WechatTextInputSegmentationTests.cs

@@ -0,0 +1,47 @@
+using WxAgent.Core;
+using Xunit;
+
+namespace WxAgent.Core.Tests;
+
+public sealed class WechatTextInputSegmentationTests
+{
+    [Fact]
+    public void SplitForSendSplitsLongTextAtTheSingleMessageBoundary()
+    {
+        var text = new string('x', WechatTextInput.MaxSegmentLength + 1);
+
+        var segments = WechatTextInput.SplitForSend(text);
+
+        Assert.Equal(2, segments.Count);
+        Assert.Equal(WechatTextInput.MaxSegmentLength, segments[0].Length);
+        Assert.Equal(1, segments[1].Length);
+        Assert.Equal(text, string.Concat(segments));
+        Assert.Throws<WxAgentException>(() => WechatTextInput.Prepare(text));
+    }
+
+    [Fact]
+    public void SplitForSendDoesNotBreakACombiningTextElement()
+    {
+        var prefix = new string('x', WechatTextInput.MaxSegmentLength - 1);
+        var combiningElement = "e\u0301";
+        var text = prefix + combiningElement + "tail";
+
+        var segments = WechatTextInput.SplitForSend(text);
+
+        Assert.Equal(2, segments.Count);
+        Assert.Equal(prefix, segments[0]);
+        Assert.StartsWith(combiningElement, segments[1], StringComparison.Ordinal);
+        Assert.All(segments, segment => Assert.InRange(segment.Length, 1, WechatTextInput.MaxSegmentLength));
+        Assert.Equal(text, string.Concat(segments));
+    }
+
+    [Fact]
+    public void SplitForSendRejectsTextBeyondTheBoundedTotalLength()
+    {
+        var text = new string('x', WechatTextInput.MaxTextLength + 1);
+
+        var exception = Assert.Throws<WxAgentException>(() => WechatTextInput.SplitForSend(text));
+
+        Assert.Equal(WxAgentErrorCode.InvalidArgument, exception.Code);
+    }
+}