Two cooperating modules that wrap stream_agent_events with in-stream
recovery from provider 429s:
* rate_limit_recovery: can_recover_provider_rate_limit truth-table
guard, reroute_to_next_auto_pin (selects the next eligible auto-pin
config and reloads the LLM bundle), log_rate_limit_recovered.
* stream_loop: run_stream_loop drives stream_agent_events in a
while-True loop, delegating recovery to a flow-supplied RecoverFn
callback so new_chat and resume_chat can share the same loop while
keeping their own nonlocal state.
Add-only; not yet wired into any orchestrator.
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