`[...maybe]` over a source the checker typed wider than the iterable it
holds at run time (`T | undefined` from an indexed read under
indexed-access strictness, an optional local) and `push(...value)` over
an untyped or widened source were SC1090 refusals. They now drain through
the checked iterator walk, validating each element into the target slot,
and throw Node's not-iterable TypeError for null/undefined.
`widenedIterableType` recognises a union of exactly one iterable arm plus
unit arms; `checkedIteratorPack` is exported so the array-method spread
path reuses the same walk.
Corpus 8504 covers `[...digit]` from a `string | undefined`, a `[...any]`
array literal, a `push(...any)`, and
`push(...(provider.x ?? []))`.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
