Method getOrBuild

src/compute-engine/engine-cache.ts:20–38

(
    cacheName: string,
    build: () => T,
    purge?: (t: T) => T | undefined
  )

/**
 * MUTABLE-OBJECT DISPOSITION (ruling B3's cache inventory, ruling B12): this
 * is the engine's one GLOBAL, STRONG value retainer — its entries live as long
 * as the engine and are held by name, not weakly — so **no entry may ever hold
 * a `BoxedObject`, directly or nested inside a value**. An object stored here
 * would survive every scope, outliving the program's last reference to it, and
 * an object-derived entry could never be invalidated (a field store advances
 * no engine axis and this store records no dependencies).
 *
 * The rule is upheld by what gets stored, not by machinery: the five named
 * caches built through it hold rule sets and constant tables (simplification
 * rules, univariate-root rules, harmonization rules, the constructible
 * trigonometric-value tables), all built from the standard library and from
 * literals, with no route to a user value. It is pinned adversarially by a
 * test rather than by a guard, because adding a containment scan to a
 * name-keyed store of arbitrary payloads would cost every build a walk to
 * defend against a case no caller can currently produce.
 */
export class EngineCacheStore {
  private _entries: Record<string, CacheEntry> = {};

  getOrBuild<T>(
    cacheName: string,