Salvages the two still-relevant fixes from PR #993 onto current main:
- use a 3-tuple LOCAL delivery key so explicit/local-origin targets are not duplicated
- shut down the previous agent-loop ThreadPoolExecutor when resizing the global pool
Adds regression tests for both behaviors.
- environments/__init__.py: try/except on atroposlib imports so
submodules like tool_call_parsers remain importable standalone
- test_agent_loop.py, test_tool_call_parsers.py,
test_managed_server_tool_support.py: skip at module level when
atroposlib is missing