Discord drops an empty outbound message instead of sending it (#78815)

* fix(discord): reject empty outbound messages

* test(discord): cover empty final reply backfill state

Missed-message backfill decides what to replay from discord_messages, so
a dropped final reply must be recorded as failed by the new guard the
same way the exception path records one — otherwise the reply is both
never sent and never retried.

Co-authored-by: Jony <619963502@qq.com>

* chore: map 619963502@qq.com to zyz619963502zyz for PR #73449 salvage

---------

Co-authored-by: Jony <619963502@qq.com>

contributors/emails/619963502@qq.com

@@ -0,0 +1,2 @@
+zyz619963502zyz
+# PR #73449 salvage → #78815

plugins/platforms/discord/adapter.py

@@ -23,6 +23,7 @@ import subprocess
 import tempfile
 import threading
 import time
+import traceback
 from collections import defaultdict
 from contextlib import suppress
 from typing import Callable, Dict, List, Optional, Any, Tuple
@@ -3040,6 +3041,29 @@ class DiscordAdapter(BasePlatformAdapter):
         """
         if not self._client:
             return SendResult(success=False, error="Not connected")
+        if not (content or "").strip():
+            logger.warning(
+                "[%s] Dropped empty message to chat=%s (caller bug). Call site:\n%s",
+                self.name,
+                chat_id,
+                "".join(traceback.format_stack(limit=12)[:-1]),
+            )
+            result = SendResult(
+                success=False,
+                error="Refusing to send empty message",
+            )
+            # Mirror the exception path's recovery bookkeeping. Missed-message
+            # backfill decides what to replay from this table, so a dropped
+            # final reply must be recorded as failed — otherwise the reply is
+            # both never sent and never retried.
+            await asyncio.to_thread(
+                self._record_discord_response,
+                reply_to=reply_to,
+                result=result,
+                content=content,
+                final=bool(metadata and metadata.get("notify")),
+            )
+            return result
 
         try:
             # Determine target channel: thread_id in metadata takes precedence.

tests/gateway/test_discord_send.py

@@ -47,6 +47,41 @@ _ensure_discord_mock()
 from plugins.platforms.discord.adapter import DiscordAdapter  # noqa: E402
 
 
+@pytest.mark.asyncio
+async def test_send_rejects_whitespace_and_records_failed_final_reply(
+    caplog, monkeypatch, tmp_path
+):
+    monkeypatch.setenv("HERMES_HOME", str(tmp_path))
+    monkeypatch.setenv("DISCORD_MISSED_MESSAGE_BACKFILL", "true")
+    adapter = DiscordAdapter(PlatformConfig(enabled=True, token="***"))
+    channel = SimpleNamespace(send=AsyncMock())
+    get_channel = MagicMock(return_value=channel)
+    adapter._client = SimpleNamespace(
+        get_channel=get_channel,
+        fetch_channel=AsyncMock(),
+    )
+    with caplog.at_level("WARNING"):
+        result = await adapter.send(
+            "555",
+            "  \n\t ",
+            reply_to="123",
+            metadata={"notify": True},
+        )
+
+    assert result.success is False
+    assert result.error == "Refusing to send empty message"
+    get_channel.assert_not_called()
+    channel.send.assert_not_awaited()
+    row = adapter._with_discord_recovery_db(
+        lambda conn: conn.execute(
+            "SELECT status, replied, outage_response, response_message_id "
+            "FROM discord_messages WHERE message_id='123'"
+        ).fetchone()
+    )
+    assert tuple(row) == ("failed", 0, 0, None)
+    assert "Dropped empty message to chat=555" in caplog.text
+
+
 def _voice_adapter(reference_obj, *, native_result=None, native_error=None):
     adapter = DiscordAdapter(PlatformConfig(enabled=True, token="***"))
     ref_msg = SimpleNamespace(id=99, to_reference=MagicMock(return_value=reference_obj))