Resolve MCP session deadlock with thread-safe per-transport locking

[gotsysdba]

Fixes #112

Fixes a deadlock where get_or_create_session() called from async methods (MCPTool.run_async, MCPToolBox._get_tools_inner_async) blocked on the portal's own event loop, and a TOCTOU race condition where concurrent callers could create duplicate sessions for the same transport.

Changes:

• tools.py: Offload get_or_create_session() to a worker thread via anyio.to_thread.run_sync in both MCPTool.run_async and MCPToolBox._get_tools_inner_async, so the event loop is never blocked
• _session_persistence.py: Replace the direct _create_long_lived_session call with a per-transport double-checked locking pattern:
  • Fast-path check before any lock (existing behavior)
  • Global _lock held briefly only to get/create a per-transport threading.Lock
  • Transport lock serializes same-transport session creation (prevents duplicates) while allowing different transports to proceed in parallel
  • Re-check under transport lock before creating

[dhilloulinoracle]

Thank you @gotsysdba for the PR!

@paul-cayet will review it

[sonleoracle]

Could you add regression coverage for the behavior this PR is changing?

For instance:

• Concurrent cold session creation for the same transport/conversation: A good test would call AsyncRuntime.get_or_create_session() from two threads at the same time and assert that only one session is created and both callers get the same session back.

• Async cold session creation should not block the event loop: Since this PR moves get_or_create_session() behind to_thread.run_sync(...) in MCPTool.run_async() and MCPToolBox.get_tools_async(), it would be good to add tests that schedule a small heartbeat task alongside those calls and assert the heartbeat still runs while session creation is in progress.

You could add them to wayflowcore/tests/mcptools/test_mcp_tools.py near the existing session-persistence tests around line 260.

[gotsysdba]

@sonleoracle, added tests:

1. test_concurrent_cold_session_creation_returns_same_session: Submits two concurrent get_or_create_session() calls for the same transport via a ThreadPoolExecutor and asserts both callers get back the exact same session object (is identity check).
2. test_async_session_creation_does_not_block_event_loop: Runs a heartbeat coroutine alongside MCPToolBox.get_tools_async() and asserts the heartbeat ticked multiple times, proving the event loop wasn't blocked during session creation.
3. test_async_mcp_tool_run_does_not_block_event_loop: Same heartbeat pattern but exercises MCPTool.run_async(), validating the to_thread.run_sync() change

---

================================================================= 3 passed in 2.32s =================================================================
% LLAMA_API_URL=x OSS_API_URL=x LLAMA70BV33_API_URL=x OLLAMA8BV32_API_URL=x OCI_REASONING_MODEL=x GEMMA_API_URL=x COMPARTMENT_ID=x \
INSTANCE_PRINCIPAL_ENDPOINT_BASE_URL=x E5largev2_EMBEDDING_API_URL=x OLLAMA_EMBEDDING_API_URL=x \
pytest wayflowcore/tests/mcptools/test_mcp_tools.py::test_concurrent_cold_session_creation_returns_same_session \
wayflowcore/tests/mcptools/test_mcp_tools.py::test_async_session_creation_does_not_block_event_loop \
wayflowcore/tests/mcptools/test_mcp_tools.py::test_async_mcp_tool_run_does_not_block_event_loop -v
================================================================ test session starts ================================================================
platform darwin -- Python 3.14.3, pytest-7.4.4, pluggy-1.6.0
cachedir: .pytest_cache
configfile: setup.cfg
plugins: anyio-4.11.0, xdist-3.8.0
collected 3 items                                                                                                                                   

wayflowcore/tests/mcptools/test_mcp_tools.py::test_concurrent_cold_session_creation_returns_same_session PASSED                               [ 33%]
wayflowcore/tests/mcptools/test_mcp_tools.py::test_async_session_creation_does_not_block_event_loop PASSED                                    [ 66%]
wayflowcore/tests/mcptools/test_mcp_tools.py::test_async_mcp_tool_run_does_not_block_event_loop PASSED                                        [100%]

================================================================= 3 passed in 2.37s =================================================================

[dhilloulinoracle]

Internal regression failed: Build ID #748

[dhilloulinoracle]

Internal regression succeeded 🍏: Build ID #749

[dhilloulinoracle]

Merge Gate INPROGRESS

[dhilloulinoracle]

Internal regression succeeded 🍏: Build ID #1540

[dhilloulinoracle]

Merge Gate succeeded 🍏: Build ID #2280