Run Gauntlet Challenge

Present challenges from the knowledge base and evaluate answers.

When NOT To Use

• The knowledge base does not exist yet (use gauntlet:extract)
• A staged path for a new contributor (use gauntlet:onboard)

In-Loop Provider Setup

Before generating a challenge, register the in-loop variation provider so we do not call out to the Anthropic API just to spawn a sibling Claude (issue #464). Outside Claude Code this is a no-op and the default Anthropic provider remains active.