insertMediaFromFile

Insert a media block of type from a local File. The block appears at once (pending, with a local preview), the bytes are hashed and written to the local store (ADR 014), then the block gets its nabu-asset:sha256-… ref: ready, or — with a host (files.onBeforePersist) — still pending while the background upload runs (block.progress, block.retry(), block.cancel()); the ref never changes afterwards. A file over files.maxFileSize is refused: the block is created rejected, with no ref and a readable reason.