Function mergeRoutingConfig

src/proxy.ts:1370–1396

* Merge partial routing config overrides with defaults.

(overrides?: Partial<RoutingConfig>)

 * Merge partial routing config overrides with defaults.
 */
function mergeRoutingConfig(overrides?: Partial<RoutingConfig>): RoutingConfig {
  if (!overrides) return DEFAULT_ROUTING_CONFIG;
  // Merge tier sets per-tier so users can override a single tier
  // (e.g. just COMPLEX) without having to redefine all four.
  // `null` explicitly disables a tier set (e.g. `agenticTiers: null` forces
  // all requests through regular tiers even when tools are present).
  const mergeTiers = (
    defaults: RoutingConfig["tiers"] | null | undefined,
    user: Partial<RoutingConfig["tiers"]> | null | undefined,
  ): RoutingConfig["tiers"] | null => {
    if (user === null) return null;
    if (user === undefined) return defaults ?? null;
    return { ...(defaults ?? {}), ...user } as RoutingConfig["tiers"];
  };
  return {
    ...DEFAULT_ROUTING_CONFIG,
    ...overrides,
    classifier: { ...DEFAULT_ROUTING_CONFIG.classifier, ...overrides.classifier },
    scoring: { ...DEFAULT_ROUTING_CONFIG.scoring, ...overrides.scoring },
    tiers:
      mergeTiers(DEFAULT_ROUTING_CONFIG.tiers, overrides.tiers) ?? DEFAULT_ROUTING_CONFIG.tiers,
    agenticTiers: mergeTiers(DEFAULT_ROUTING_CONFIG.agenticTiers, overrides.agenticTiers),
    ecoTiers: mergeTiers(DEFAULT_ROUTING_CONFIG.ecoTiers, overrides.ecoTiers),
    premiumTiers: mergeTiers(DEFAULT_ROUTING_CONFIG.premiumTiers, overrides.premiumTiers),
    overrides: { ...DEFAULT_ROUTING_CONFIG.overrides, ...overrides.overrides },
  };
}

/**
 * Build the `usage.cost` breakdown that ClawRouter injects into responses.