The MCP circuit breaker in tools/mcp_tool.py has no half-open state and
no reset-on-reconnect behavior, so once it trips after 3 consecutive
failures it stays tripped for the process lifetime. These tests lock
in the intended recovery behavior:
1. test_circuit_breaker_half_opens_after_cooldown — after the cooldown
elapses, the next call must actually probe the session; success
closes the breaker.
2. test_circuit_breaker_reopens_on_probe_failure — a failed probe
re-arms the cooldown instead of letting every subsequent call
through.
3. test_circuit_breaker_cleared_on_reconnect — a successful OAuth
recovery resets the breaker even if the post-reconnect retry
fails (a successful reconnect is sufficient evidence the server
is viable again).
All three currently fail, as expected.
