A blocked RebalancePlan places zero orders but the account keeps its prior positions, so
plan_and_record must not advance the multistrat_exec_pos basis or book a forward_record in that
case — otherwise every subsequent executed return is computed against a phantom target book that
was never placed. Also wires CockpitBacktestRefProvider to alias multistrat_exec -> multistrat so
the reconciliation gate actually reconciles the executed track against the modeled book's
basis-matched backtest reference, as the registry comment already (incorrectly) claimed. Plus a
doc comment clarifying positions_after is the intended target basis, and type-annotated locals in
compute_exec_return to keep the inferred return type float instead of Any.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
