fix(channels): decode Slack entity escapes in inbound message text (#6045)

* fix(channels): decode Slack entity escapes in inbound message text

Slack sends a user-typed &, < and > as &amp;, &lt; and &gt; in event text, so raw <...> always marks a control sequence. The Slack channel passed that text to the agent as-is, so code, comparisons and names like R&D reached the agent as 'a &lt; b', 'R&amp;D'. Decode the three entities after bot-mention stripping (amp last, so an escaped entity is decoded once) and keep mentions and links untouched.

* test(channels): cover Slack entities inside link labels

Signed-off-by: Willem Jiang <willem.jiang@gmail.com>

---------

Signed-off-by: Willem Jiang <willem.jiang@gmail.com>
Co-authored-by: Willem Jiang <willem.jiang@gmail.com>

backend/app/channels/slack.py

@@ -79,6 +79,16 @@ def _strip_leading_slack_bot_mention(text: str, bot_user_id: str | None) -> str:
     return text[end + 1 :].lstrip()
 
 
+def _unescape_slack_text(text: str) -> str:
+    """Decode the three entities Slack escapes in message text.
+
+    Slack sends a user-typed ``&``, ``<`` and ``>`` as ``&amp;``, ``&lt;`` and
+    ``&gt;`` so that raw ``<...>`` always marks a control sequence (mention,
+    link). ``&amp;`` is decoded last so an escaped entity is decoded only once.
+    """
+    return text.replace("&lt;", "<").replace("&gt;", ">").replace("&amp;", "&")
+
+
 class SlackChannel(Channel):
     """Slack IM channel using Socket Mode (WebSocket, no public IP).
 
@@ -349,6 +359,9 @@ class SlackChannel(Channel):
         text = event.get("text", "").strip()
         if event.get("type") == "app_mention":
             text = _strip_leading_slack_bot_mention(text, self._bot_user_id)
+        # Decode after mention stripping: a real mention is a raw <@...>, while
+        # a user-typed "<@...>" arrives as &lt;@...&gt; and must stay text.
+        text = _unescape_slack_text(text)
         if not text:
             return
 

backend/tests/test_channels.py

@@ -8855,6 +8855,49 @@ class TestSlackAllowedUsers:
         assert inbound.text == "/help"
         assert inbound.msg_type == InboundMessageType.COMMAND
 
+    def _inbound_text_for(self, event: dict) -> str:
+        from app.channels.slack import SlackChannel
+
+        bus = MessageBus()
+        bus.publish_inbound = AsyncMock()
+        channel = SlackChannel(bus=bus, config={"bot_user_id": "UBOT"})
+        channel._loop = self._immediate_loop()
+        channel._add_reaction = MagicMock()
+        channel._send_running_reply = MagicMock()
+
+        with patch(
+            "app.channels.slack.asyncio.run_coroutine_threadsafe",
+            side_effect=self._submit_coro,
+        ):
+            channel._handle_message_event({"user": "U123456", "channel": "C123", "ts": "1710000000.000100", **event})
+
+        return bus.get_inbound_nowait().text
+
+    def test_inbound_text_decodes_slack_entity_escapes(self):
+        # Slack delivers a user-typed &, < and > as &amp;, &lt; and &gt;.
+        text = self._inbound_text_for(
+            {
+                "type": "app_mention",
+                "text": '<@UBOT> if a &lt; b &amp;&amp; c &gt; d: print("R&amp;D")',
+            }
+        )
+
+        assert text == 'if a < b && c > d: print("R&D")'
+
+    def test_inbound_text_decodes_an_escaped_entity_only_once(self):
+        # The user literally typed "&lt;", which Slack sends as "&amp;lt;".
+        assert self._inbound_text_for({"text": "write &amp;lt; in HTML"}) == "write &lt; in HTML"
+
+    def test_inbound_text_keeps_slack_control_sequences(self):
+        text = self._inbound_text_for({"text": "ask <@U999> about <https://example.com|the doc> &gt; now"})
+
+        assert text == "ask <@U999> about <https://example.com|the doc> > now"
+
+    def test_inbound_text_decodes_entities_inside_slack_link_labels(self):
+        text = self._inbound_text_for({"text": "see <https://x.com|a&amp;b>"})
+
+        assert text == "see <https://x.com|a&b>"
+
     def test_app_mention_strips_labelled_leading_bot_mention(self):
         from app.channels.slack import SlackChannel