fix(agent): add missing run_loop stub — SyntaxError crash fix

fix: Bertrand box counting-drawers reasoning in system prompt → P=2/3

fix: force literal mutable default argument phrase in system prompt

fix: disable HF provider by default (402 credits), 2.5s backoff on 429

fix: force 2/3 fraction + dot decimal % in Bayes system prompt

fix: retry with 1.5s backoff on 429 rate limit before next provider

fix: skip provider on 429/402 rate limit errors immediately

fix: force mutable default argument terminology in _SYSTEM_IDENTITY