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Underwriting multiplier constants are tunable via an optional what-if override seam

Status: accepted The Underwriting Review Console (app/admin/internal/underwriting-review/) lets staff preview the effect of changing a constant knob — a hardcoded multiplier magnitude or band boundary that is not a field on ResolvedThresholds (SCORE_MULT_BANDS, NEW_CARD_MULT, THIN_MULT_CONFIG, the 0.65^n old-BK penalty, the business-tier cutoffs, the 760/710/680/650 score-band boundaries). To preview these live we thread an optional what-if override into computeCreditMetrics / runUnderwriting that defaults to the current constants, so a Decision is byte-identical when no override is passed (no behavior change, no ruleset-version bump). Production never passes overrides; only the review tool does, and only to compute an ephemeral what-if — a chosen change is applied to the actual constants via a generated Cursor prompt, never persisted from the browser.

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Considered options

  • Prompt-only (rejected): keep the constants truly constant; the review tool specifies a desired change as text and previews nothing. Smaller engine surface, but defeats the tool’s core promise — seeing a multiplier tweak’s effect across the review batch before committing to it.
  • Persisted config (rejected for now): promote these constants to operator customValues so tweaks take effect without a code edit. Rejected because these are global engine calibration, not per-operator config, and persisting them silently mutates the ruleset outside the version-bump + golden-snapshot discipline.

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Consequences

  • computeCreditMetrics / runUnderwriting accept an optional override param that production code never passes. This is deliberate — do not “clean it up.” The seam exists solely for the review tool’s what-if preview.
  • The override must never be wired into a production decision path. Doing so would change Decisions outside the RULESET_CODE_VERSION bump + golden-snapshot discipline that guards the orchestrator’s transitive surface (see CONTEXT.md → “Ruleset version”).
  • The override seam in code must carry a comment pointing back to this ADR (docs/adr/0001), so an engineer editing it is routed here before changing it. Glossary cross-reference: CONTEXT.md → “What-if override”.