feat: Tradier broker mirror — config-switch redundancy for Alpaca execution
tradier_broker/ mirrors every trading call the live loop makes on
AlpacaPaperClient (account, clock, positions, orders, submit incl.
bracket->OTOCO, cancel, replace, close) with identical signatures and
Alpaca-shaped returns, so trading_execution / exit_manager / flatten /
execution / sync run unchanged. Market data always delegates to Alpaca.
- BROKER=tradier (+ TRADIER_* env) swaps execution client in run_live_paper;
default path untouched
- client_order_id -> tag preserves the lost-submit reconcile
- TradierApiError subclasses AlpacaApiError so the executor's
rejection-vs-transport fork works as-is
- sandbox-verified: balances/clock/positions/orders, OTOCO preview
(result:true), place -> tag lookup -> cancel round trip
- 18 unit tests (translation + client paths); executor integration checked
- docs/TRADIER-FALLBACK.md switch runbook
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
