The wire format produced by the decoder (DecodedResult) represents the TypeScript type graph as a pair of flat maps keyed by TypeKey: one for structural types (TsType) and one for export declarations (TsExportDeclaration). References between types are expressed as TypeKey values that must be resolved against those maps. While correct, this representation is inconvenient for generators: maps must be threaded through every rendering function, and every type dereference requires an explicit lookup.

ArenaInterner pre-resolves this key graph into a lazy object graph. Each TypeKey reference becomes a Lazy<ResolvedType> — following a reference is simply forcing a lazy value, with no map access needed at call sites. Results are memoised in a dictionary keyed by TypeKey, so types that share the same key resolve to the same object instance. Combined with [<ReferenceEquality>] on all record types, this enables identity-based sharing detection in generators (e.g. recognising that two members reference the same TypeParameter) without carrying keys around.

Cycles in the type graph (e.g. recursive interfaces, self-referential type aliases) are broken naturally by the lazy boundaries around all TypeKey dereferences. Construction of a node never forces any of its outgoing lazy references, so re-entrant calls to resolve cannot occur during graph initialisation. By the time a consumer forces a lazy, the referent is already in the cache.

• Rendering functions should not need access to global maps.
• Structural sharing or identity equality between types is meaningful to the output.
• The generator traverses the type graph recursively (pattern matching on ResolvedType is more ergonomic than repeated map lookups).

• Only a small subset of the type graph is needed — the interner allocates shells for all top-level exports at construction time.
• TypeKey identity must be preserved for output naming or cross-referencing (keys are not carried in the resolved graph).
• Startup cost is a concern — ArenaInterner.create walks and shells the entire export map eagerly, deferring only nested type resolution.