runSubmitAgent moved verbatim from extraction.ts to src/agent/subagents/
submit-agent.ts (exported; extraction imports it — zero behavior change,
extraction suites green untouched). New optional prepareArguments seam:
extraction wires its healStringifiedArrays heal; default is identity
pass-through. ModelRole += partitioner | problemGenerator | grader;
ROLE_SLOT pins all three to strong (quality-critical trio, plan default).
Note: BACKGROUND_MODEL_ROLES (per-role settings overrides) deliberately
NOT extended — settings-surface decision, flagged for the planning
session.
