diff --git a/plugins/platforms/slack/adapter.py b/plugins/platforms/slack/adapter.py
index 97a39f4708..2addcd8a66 100644
--- a/plugins/platforms/slack/adapter.py
+++ b/plugins/platforms/slack/adapter.py
@@ -4301,8 +4301,8 @@ class SlackAdapter(BasePlatformAdapter):
             return None
         if await self._drop_bot_sender(event):
             return None
-        # Edits were normalized above so an @mention added by edit can wake the bot once,
-        # which also means their subtype is gone by the time this check runs.
+        # Edits were normalized above so an @mention added by edit can wake the bot once;
+        # the normalized event retains the edited message's own subtype.
         # Housekeeping subtypes (joins/leaves, topic/name/purpose changes, convert_to_private/
         # public, pins, deletions, file comments...) are not a person speaking, so they must
         # not start a turn in free-response channels (#110778). Allowlist rather than denylist
@@ -4311,8 +4311,13 @@ class SlackAdapter(BasePlatformAdapter):
         # ``file_shared`` fallback synthesizes exactly this subtype. ``thread_broadcast``
         # passes: a human sharing a threaded reply into the channel carries user/text.
         # ``me_message`` passes: ``/me`` is a person speaking.
+        # ``bot_message`` already passed allow_bots above; document_mention is an
+        # explicit app mention from a Slack canvas, not a lifecycle notification.
         subtype = event.get("subtype")
-        if subtype not in (None, "", "file_share", "thread_broadcast", "me_message"):
+        if subtype not in (
+            None, "", "file_share", "thread_broadcast", "me_message",
+            "bot_message", "document_mention",
+        ):
             logger.debug(
                 "[Slack] Dropping non-conversational message subtype=%s in channel %s",
                 subtype, channel_id)
diff --git a/tests/gateway/test_slack_conversational_senders.py b/tests/gateway/test_slack_conversational_senders.py
new file mode 100644
index 0000000000..71431e4efb
--- /dev/null
+++ b/tests/gateway/test_slack_conversational_senders.py
@@ -0,0 +1,92 @@
+"""Preserve conversational senders through the subtype filter in PR #110780."""
+
+from types import SimpleNamespace
+from unittest.mock import AsyncMock
+
+import pytest
+
+from gateway.config import PlatformConfig
+from plugins.platforms.slack.adapter import SlackAdapter
+
+
+@pytest.fixture
+def adapter():
+    instance = SlackAdapter(PlatformConfig(
+        enabled=True,
+        token="xoxb-test",
+        extra={"free_response_channels": ["C_TEST"], "allow_bots": "all"},
+    ))
+    instance._bot_user_id = "U_BOT"
+    instance._running = True
+    instance._app = SimpleNamespace(client=SimpleNamespace(
+        users_info=AsyncMock(return_value={
+            "ok": True, "user": {"is_bot": False, "real_name": "Test User"},
+        }),
+        conversations_info=AsyncMock(return_value={
+            "ok": True, "channel": {"name": "test"},
+        }),
+        conversations_replies=AsyncMock(return_value={"ok": True, "messages": []}),
+    ))
+    instance.handle_message = AsyncMock()
+    return instance
+
+
+def _event(subtype, text, *, edited):
+    message = {
+        "type": "app_mention" if subtype == "document_mention" else "message",
+        "subtype": subtype, "user": "U_TEST", "text": text,
+        "channel": "C_TEST", "channel_type": "channel", "team": "T_TEST",
+        "ts": "100.000001",
+    }
+    if subtype == "bot_message":
+        message["bot_id"] = "B_OTHER"
+    else:
+        message["document_mention"] = {
+            "file_id": "F_CANVAS", "section_id": "section-1",
+            "mentioning_user_ids": ["U_TEST"],
+        }
+    if not edited:
+        return message
+    return {
+        "type": "message", "subtype": "message_changed",
+        "channel": "C_TEST", "channel_type": "channel", "team": "T_TEST",
+        "ts": "101.000001", "event_ts": "101.000001", "message": message,
+    }
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize("edited", [False, True], ids=["original", "edited"])
+@pytest.mark.parametrize(("policy", "mentioned", "accepted"), [
+    ("none", False, False),
+    ("none", True, False),
+    ("mentions", False, False),
+    ("mentions", True, True),
+    ("all", False, True),
+])
+async def test_bot_messages_retain_the_configured_policy(adapter, policy, mentioned, accepted, edited):
+    adapter.config.extra["allow_bots"] = policy
+    text = "<@U_BOT> A message" if mentioned else "A message"
+
+    await adapter._handle_slack_message(_event("bot_message", text, edited=edited))
+
+    assert adapter.handle_message.await_count == int(accepted)
+    if accepted:
+        delivered = adapter.handle_message.await_args.args[0]
+        assert delivered.text == "A message"
+        assert delivered.source.is_bot is True
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize("edited", [False, True], ids=["original", "edited"])
+async def test_canvas_mentions_reach_the_agent(adapter, edited):
+    adapter.config.extra = {"allow_bots": "none"}
+
+    await adapter._handle_slack_message(
+        _event("document_mention", "<@U_BOT> Summarize this canvas", edited=edited)
+    )
+
+    adapter.handle_message.assert_awaited_once()
+    delivered = adapter.handle_message.await_args.args[0]
+    assert delivered.text == "Summarize this canvas"
+    assert delivered.source.user_id == "U_TEST"
+    assert delivered.raw_message["document_mention"]["file_id"] == "F_CANVAS"