fix(discord): retry without reply reference for system messages

gateway/platforms/discord.py

@@ -605,10 +605,30 @@ class DiscordAdapter(BasePlatformAdapter):
                     logger.debug("Could not fetch reply-to message: %s", e)
             
             for i, chunk in enumerate(chunks):
-                msg = await channel.send(
-                    content=chunk,
-                    reference=reference if i == 0 else None,
-                )
+                chunk_reference = reference if i == 0 else None
+                try:
+                    msg = await channel.send(
+                        content=chunk,
+                        reference=chunk_reference,
+                    )
+                except Exception as e:
+                    err_text = str(e)
+                    if (
+                        chunk_reference is not None
+                        and "error code: 50035" in err_text
+                        and "Cannot reply to a system message" in err_text
+                    ):
+                        logger.warning(
+                            "[%s] Reply target %s is a Discord system message; retrying send without reply reference",
+                            self.name,
+                            reply_to,
+                        )
+                        msg = await channel.send(
+                            content=chunk,
+                            reference=None,
+                        )
+                    else:
+                        raise
                 message_ids.append(str(msg.id))
             
             return SendResult(

tests/gateway/test_discord_send.py

@@ -0,0 +1,76 @@
+from types import SimpleNamespace
+from unittest.mock import AsyncMock, MagicMock
+import sys
+
+import pytest
+
+from gateway.config import PlatformConfig
+
+
+def _ensure_discord_mock():
+    if "discord" in sys.modules and hasattr(sys.modules["discord"], "__file__"):
+        return
+
+    discord_mod = MagicMock()
+    discord_mod.Intents.default.return_value = MagicMock()
+    discord_mod.Client = MagicMock
+    discord_mod.File = MagicMock
+    discord_mod.DMChannel = type("DMChannel", (), {})
+    discord_mod.Thread = type("Thread", (), {})
+    discord_mod.ForumChannel = type("ForumChannel", (), {})
+    discord_mod.ui = SimpleNamespace(View=object, button=lambda *a, **k: (lambda fn: fn), Button=object)
+    discord_mod.ButtonStyle = SimpleNamespace(success=1, primary=2, danger=3, green=1, blurple=2, red=3)
+    discord_mod.Color = SimpleNamespace(orange=lambda: 1, green=lambda: 2, blue=lambda: 3, red=lambda: 4)
+    discord_mod.Interaction = object
+    discord_mod.Embed = MagicMock
+    discord_mod.app_commands = SimpleNamespace(describe=lambda **kwargs: (lambda fn: fn))
+
+    ext_mod = MagicMock()
+    commands_mod = MagicMock()
+    commands_mod.Bot = MagicMock
+    ext_mod.commands = commands_mod
+
+    sys.modules.setdefault("discord", discord_mod)
+    sys.modules.setdefault("discord.ext", ext_mod)
+    sys.modules.setdefault("discord.ext.commands", commands_mod)
+
+
+_ensure_discord_mock()
+
+from gateway.platforms.discord import DiscordAdapter  # noqa: E402
+
+
+@pytest.mark.asyncio
+async def test_send_retries_without_reference_when_reply_target_is_system_message():
+    adapter = DiscordAdapter(PlatformConfig(enabled=True, token="***"))
+
+    ref_msg = SimpleNamespace(id=99)
+    sent_msg = SimpleNamespace(id=1234)
+    send_calls = []
+
+    async def fake_send(*, content, reference=None):
+        send_calls.append({"content": content, "reference": reference})
+        if len(send_calls) == 1:
+            raise RuntimeError(
+                "400 Bad Request (error code: 50035): Invalid Form Body\n"
+                "In message_reference: Cannot reply to a system message"
+            )
+        return sent_msg
+
+    channel = SimpleNamespace(
+        fetch_message=AsyncMock(return_value=ref_msg),
+        send=AsyncMock(side_effect=fake_send),
+    )
+    adapter._client = SimpleNamespace(
+        get_channel=lambda _chat_id: channel,
+        fetch_channel=AsyncMock(),
+    )
+
+    result = await adapter.send("555", "hello", reply_to="99")
+
+    assert result.success is True
+    assert result.message_id == "1234"
+    assert channel.fetch_message.await_count == 1
+    assert channel.send.await_count == 2
+    assert send_calls[0]["reference"] is ref_msg
+    assert send_calls[1]["reference"] is None