fix(slack): warn when slack_tokens.json is group/world-readable

The OAuth multi-workspace token file contains plaintext bot tokens for
all saved Slack workspaces. Unlike the Google Chat adapter which sets
0o600 when writing credentials, the Slack token file has no permission
enforcement — a default umask 022 makes it world-readable.

Fix: check file permissions on read and emit a warning log with remediation
instructions if the file is group- or world-readable.

plugins/platforms/slack/adapter.py

@@ -1623,6 +1623,19 @@ class SlackAdapter(BasePlatformAdapter):
         tokens_file = get_hermes_home() / "slack_tokens.json"
         if tokens_file.exists():
             try:
+                # Warn if the token file is world- or group-readable — it
+                # contains plaintext bot tokens for all saved workspaces.
+                import stat as _stat
+
+                mode = tokens_file.stat().st_mode
+                if mode & (_stat.S_IRGRP | _stat.S_IROTH):
+                    logger.warning(
+                        "[Slack] %s is group/world-readable (mode 0%o). "
+                        "Run: chmod 600 %s",
+                        tokens_file.name,
+                        _stat.S_IMODE(mode),
+                        tokens_file,
+                    )
                 saved = json.loads(tokens_file.read_text(encoding="utf-8"))
                 for team_id, entry in saved.items():
                     tok = entry.get("token", "") if isinstance(entry, dict) else ""