fix: bot-lint nits — drop unused imports, add reason to except

Resolves three github-code-quality threads blocking PR-2739 merge:
- workspace/tests/test_mcp_cli_multi_workspace.py: remove unused
  `import os` and `from unittest.mock import patch` (left over from
  an earlier test draft that mocked at the os.environ layer).
- workspace/mcp_cli.py:523: replace bare `pass` in the
  register_workspace_token ImportError handler with a debug log line +
  one-line comment explaining the silent-degrade contract (older
  installs that don't yet ship the helper fall back to the legacy
  single-token path; single-workspace operators see no behavior
  change).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

workspace/mcp_cli.py

@@ -521,7 +521,10 @@ def main() -> None:
         for wsid, tok in workspaces:
             register_workspace_token(wsid, tok)
     except ImportError:
-        pass
+        # Older installs that don't yet ship register_workspace_token —
+        # multi-workspace resolution silently degrades to the legacy
+        # single-token path; single-workspace operators see no change.
+        logger.debug("platform_auth.register_workspace_token unavailable; skipping registry populate")
 
     # Standalone-mode register + heartbeat. Skipped via env var so an
     # in-container caller (which has its own heartbeat loop) can reuse

workspace/tests/test_mcp_cli_multi_workspace.py

@@ -8,10 +8,8 @@ breaks multi-workspace doesn't get hidden in a 1000-line test file.
 from __future__ import annotations
 
 import json
-import os
 import sys
 from pathlib import Path
-from unittest.mock import patch
 
 import pytest