The long tail of engine-held values: iteration, promises crossing, and the driver through its plugin pipeline

- for-of, destructuring, and spread over engine-held dyn values ride the engine's own iterator protocol with V8's exact non-iterable spellings; for-of over dyn lowers generally
- Static promises cross into the engine as thenables; Promise.all over mixed and non-literal entries runs the engine's own combinator; engine-array fulfillments exit by reference
- The re-minted silent-wrong-answer path is closed: island-literal members whose values poison fence at the read with the captured diagnostic
- The checked-dynamic tree replaces the old nickname across comments and internal docs