Extends reasoning_effort to accept 'adaptive' in addition to
low/medium/high. When set, uses Anthropic's type: 'adaptive'
thinking API instead of a fixed budget, letting the model decide
when and how much to think per turn.
Also auto-enables interleaved thinking between tool calls on
claude-sonnet-4-6 and claude-opus-4-6.
Usage:
"reasoning_effort": "adaptive" in agents.defaults config
