test: add regression tests for IRC multi-line message formatting

docs/changelog/v0.2.17.md

@@ -6,4 +6,4 @@
 
 ## Bug Fixes
 
-- **IRC multi-line messages** — sending a message with line breaks from the TUI now correctly delivers each line as a separate PRIVMSG to IRC clients. Previously newlines were embedded raw in the IRC frame, which could create invalid messages.
+- **IRC multi-line messages** — sending a message with line breaks from the TUI now correctly delivers each line as a separate PRIVMSG to IRC clients. Previously newlines were embedded raw in the IRC frame, so IRC clients silently dropped everything after the first line — most visibly, a link on its own line disappeared while its embed preview still showed.

src/EchoHub.Tests/Irc/IrcMessageFormatterTests.cs

@@ -242,6 +242,36 @@ public class IrcMessageFormatterTests
         Assert.Equal("", chunks[0]);
     }
 
+    [Fact]
+    public void FormatMessage_UrlOnOwnLine_EmitsUrlAsItsOwnPrivmsg()
+    {
+        // Regression: multi-line content used to go out as ONE line with a raw \n
+        // embedded. IRC clients drop everything after the newline as a malformed
+        // frame, so a URL on its own line silently vanished while the embed lines
+        // (separate, valid PRIVMSGs) still rendered.
+        var embeds = new List<EmbedDto>
+        {
+            new("Example Site", "Page Title", "Description", null, "https://example.com")
+        };
+        var msg = CreateTextMessage("check this out\nhttps://example.com", embeds: embeds);
+        var lines = IrcMessageFormatter.FormatMessage(msg);
+
+        Assert.Contains(lines, l => l.EndsWith("PRIVMSG #general :check this out"));
+        Assert.Contains(lines, l => l.EndsWith("PRIVMSG #general :https://example.com"));
+        Assert.All(lines, l => Assert.DoesNotContain('\n', l));
+        Assert.All(lines, l => Assert.DoesNotContain('\r', l));
+    }
+
+    [Fact]
+    public void SplitMessage_MultiLineContent_SplitsOnNewlines()
+    {
+        var chunks = IrcMessageFormatter.SplitMessage("line one\nhttps://example.com/page", 400);
+
+        Assert.Equal(2, chunks.Count);
+        Assert.Equal("line one", chunks[0]);
+        Assert.Equal("https://example.com/page", chunks[1]);
+    }
+
     [Fact]
     public void SplitMessage_UnicodeContent_CountsUtf8Bytes()
     {