fix(slack): add bold-text zero-width-space guard for trailing non-word chars

Slack's mrkdwn parser can fail to recognize the closing * of a bold span
when it is immediately preceded by a non-word character (), ], }, ., :,
em-dash, ...), mis-rendering the span and in reported cases truncating
the rest of the message.  Insert a zero-width space (U+200B) between the
last character and the closing * whenever the last character is not
alphanumeric or underscore.

Reapplied from #35144 by @gonzalofrancoceballos — the original patched
gateway/platforms/slack.py, which was migrated to
plugins/platforms/slack/adapter.py in the plugin migration.

plugins/platforms/slack/adapter.py

@@ -3298,9 +3298,20 @@ class SlackAdapter(BasePlatformAdapter):
         )
 
         # 9) Convert bold: **text** → *text* (Slack bold)
+        # Slack's mrkdwn parser fails to recognize the closing * when it is
+        # immediately preceded by non-word characters (e.g. ), ], }, ., :, —).
+        # This causes the parser to silently truncate the rest of the message.
+        # Insert a zero-width space (U+200B) between the last character and
+        # the closing * whenever the last character is not alphanumeric or _.
+        def _convert_bold(m):
+            inner = m.group(1)
+            if inner and not (inner[-1].isalnum() or inner[-1] == "_"):
+                return _ph(f"*{inner}\u200b*")
+            return _ph(f"*{inner}*")
+
         text = re.sub(
             r"\*\*(.+?)\*\*",
-            lambda m: _ph(f"*{m.group(1)}*"),
+            _convert_bold,
             text,
         )