feat: generalize session sending with multiline text and structured mentions

Add named-session file/image/reply sending, preserve multiline text, and share safe member/all mention handling. Protect existing drafts, bind popup selection to the current window, validate structured mention tokens, and require fresh matching visible messages without automatic resend. Core tests: 121 passed. Windows 4.1.13.63 final validation: 9/9 passed. Record explicit coverage limits and sanitized evidence.

tests/WxAgent.Core.Tests/WechatMentionConfirmationTests.cs

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+using WxAgent.Core;
+using Xunit;
+
+namespace WxAgent.Core.Tests;
+
+public sealed class WechatMentionConfirmationTests
+{
+    [Theory]
+    [InlineData("\uFFFC", true)]
+    [InlineData("\uFFFC\u2005", true)]
+    [InlineData("@Hao 豪", false)]
+    [InlineData("@", false)]
+    [InlineData("\uFFFCunexpected", false)]
+    [InlineData("\uFFFC\uFFFC", false)]
+    public void RequiresExactlyOneStructuredMentionToken(string value, bool expected) =>
+        Assert.Equal(expected, WechatSendConfirmation.IsMentionToken(value));
+
+    [Theory]
+    [InlineData("@Hao 豪 marker", "Hao 豪", true)]
+    [InlineData("@Hao 豪\u2005marker", "Hao 豪", true)]
+    [InlineData("@所有人 marker", "所有人", true)]
+    [InlineData("@Hao 豪 other", "Hao 豪", false)]
+    [InlineData("@Other marker", "Hao 豪", false)]
+    public void RequiresFreshExactMentionAndBody(string text, string member, bool expected)
+    {
+        var message = new ChatMessageSnapshot(text, "fresh", 0, ChatMessageType.Text);
+        Assert.Equal(expected, WechatSendConfirmation.MatchesMention(message, new HashSet<string>(), member, "marker"));
+        Assert.False(WechatSendConfirmation.MatchesMention(message, new HashSet<string> { "fresh" }, member, "marker"));
+        Assert.False(WechatSendConfirmation.MatchesMention(message with { Type = ChatMessageType.Quote }, new HashSet<string>(), member, "marker"));
+    }
+}

tests/WxAgent.Core.Tests/WechatSendConfirmationTests.cs

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+using WxAgent.Core;
+using Xunit;
+
+namespace WxAgent.Core.Tests;
+
+public sealed class WechatSendConfirmationTests
+{
+    [Fact]
+    public void RequiresFreshMatchingTypeAndExactReplyText()
+    {
+        var baseline = new HashSet<string> { "old" };
+        var reply = new ChatMessageSnapshot("reply", "new", 0, ChatMessageType.Quote);
+        Assert.True(WechatSendConfirmation.Matches(reply, baseline, ChatMessageType.Quote, "reply"));
+        Assert.False(WechatSendConfirmation.Matches(reply with { Fingerprint = "old" }, baseline, ChatMessageType.Quote, "reply"));
+        Assert.False(WechatSendConfirmation.Matches(reply with { Type = ChatMessageType.Text }, baseline, ChatMessageType.Quote, "reply"));
+        Assert.False(WechatSendConfirmation.Matches(reply with { Text = "another reply" }, baseline, ChatMessageType.Quote, "reply"));
+    }
+
+    [Theory]
+    [InlineData("report.txt", true)]
+    [InlineData("文件\nreport.txt\n1 KB", true)]
+    [InlineData("文件\r\nreport.txt\r\n1 KB", true)]
+    [InlineData("other-report.txt", false)]
+    [InlineData("report.txt.backup", false)]
+    public void FileConfirmationRequiresExactFilenameLine(string text, bool expected)
+    {
+        var message = new ChatMessageSnapshot(text, "new", 0, ChatMessageType.File);
+        Assert.Equal(expected, WechatSendConfirmation.Matches(message, new HashSet<string>(), ChatMessageType.File, "report.txt"));
+    }
+
+    [Fact]
+    public void ImageConfirmationRejectsOtherTypesAndOldRows()
+    {
+        var message = new ChatMessageSnapshot("[图片]", "new", 0, ChatMessageType.Image);
+        Assert.True(WechatSendConfirmation.Matches(message, new HashSet<string>(), ChatMessageType.Image, null));
+        Assert.False(WechatSendConfirmation.Matches(message, new HashSet<string> { "new" }, ChatMessageType.Image, null));
+        Assert.False(WechatSendConfirmation.Matches(message with { Type = ChatMessageType.Text }, new HashSet<string>(), ChatMessageType.Image, null));
+    }
+}

tests/WxAgent.Core.Tests/WechatTextInputTests.cs

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+using WxAgent.Core;
+using Xunit;
+
+namespace WxAgent.Core.Tests;
+
+public sealed class WechatTextInputTests
+{
+    [Fact]
+    public void PreservesMultilineWhitespaceWithCanonicalLineEndings()
+    {
+        Assert.Equal("first\n\n  second\t\nthird", WechatTextInput.Prepare("first\r\n\r\n  second\t\rthird"));
+        Assert.Equal(new string('x', 4000), WechatTextInput.Prepare(new string('x', 4000)));
+        Assert.Throws<WxAgentException>(() => WechatTextInput.Prepare(new string('x', 4001)));
+    }
+
+    [Theory]
+    [InlineData("")]
+    [InlineData(" \r\n\t")]
+    [InlineData("before\0after")]
+    [InlineData("before\u001bafter")]
+    public void RejectsEmptyOrUnsafeInput(string input) =>
+        Assert.Throws<WxAgentException>(() => WechatTextInput.Prepare(input));
+
+    [Fact]
+    public void QuoteParserPreservesBlankLinesAndIndentation()
+    {
+        const string reply = "first\n\n  second  ";
+        var parsed = Assert.Single(VisibleMessageParser.Parse([reply + "\n引用 Alice 的消息 : original"]));
+        Assert.Equal(reply, parsed.Text);
+        Assert.Equal(ChatMessageType.Quote, parsed.Type);
+        Assert.True(WechatSendConfirmation.Matches(parsed, new HashSet<string>(), ChatMessageType.Quote, reply));
+        Assert.Equal("original", parsed.Quote!.Text);
+    }
+}