feat(ui): warn before sending plugin-only symbols

HellionChat/_Helpers/PluginDisclosureScanner.cs

@@ -0,0 +1,30 @@
+namespace HellionChat._Helpers;
+
+// UI-11 pure decision helper: does a message about to be sent carry a glyph
+// that only renders correctly for players running HellionChat or a similar
+// plugin? Those are FFXIV Private-Use-Area icon codepoints (the same range
+// SeIconChar covers); a recipient without a plugin sees an empty box.
+//
+// Works on raw char codepoints on purpose: SeIconChar is a Dalamud type, and a
+// helper that touched it could not run in the xUnit AppDomain
+// (feedback_dalamud_test_isolation, point 7).
+// TEST-MIRROR: ../../../Hellion Build test/Ui/PluginDisclosureScannerTests.cs
+public static class PluginDisclosureScanner
+{
+    // FFXIV packs its icon glyphs into this slice of the Unicode Private Use
+    // Area. The whole range is inside the BMP, so a single char per codepoint
+    // is enough — no surrogate-pair handling needed.
+    private const char PrivateUseFirst = '';
+    private const char PrivateUseLast = '';
+
+    public static bool ContainsPrivateUseGlyph(string text)
+    {
+        foreach (var c in text)
+        {
+            if (c >= PrivateUseFirst && c <= PrivateUseLast)
+                return true;
+        }
+
+        return false;
+    }
+}