TypeScript 5.7.3 declares iterator helpers on IteratorObject<t>, not Array<t>. A control using [1,2,3].values().filter(...).map(...).toArray() has an iterator after filter/map and an array only after toArray. Home currently accepts the chain because lib.arrayProto incorrectly has a toArray method. Removing that member exposes the real gap: checker treats the iterator object (which stores its yielded T in a numeric index slot) as an array, so filter returns T[] and map follows Array semantics. The full checker test checker: ES2025 Float16Array global and iterator helper toArray are recognized failed after removing the erroneous Array method (4733 pass / 1 fail). That removal is not yet committed.
Fix the underlying type model: recognize IteratorObject receivers before array-prototype fallback, give filter/map/take/drop/toArray and other helpers the TypeScript iterator return/callback types, preserve generic inference, and ensure Array<t> itself has no toArray. Compare TypeScript 5.7.3 controls for iterator chains and direct array.toArray, then run checker, Program, LSP and exact CLI tests under the memory guard. No name-based diagnostic suppression or Array-only proxy method.