Resolution: the fetch and load ladders

At runtime each tool collapses the bindings to one effective fetcher and loader per dataset, trying rungs in order.

Fetch ladder: own-language fetcher (explicit _LANG.<self> > bare fetcher) → shell command → cross-language fetch (rung 3) → uri download → error.

Load ladder: own-language loader (explicit > bare) → manifest format default (_LANG.<self>.loaders > _LOADERS) → built-in format default → error.

Fail-loud (spec-v3.6). A binding that is present for the running language (bare or explicit _LANG.<self>) and fails to resolve is an error; one that resolves and then raises propagates. There is no silent fall-through to a different loader/fetcher. The ladder falls through only to skip rungs that are absent for the running language (e.g. another language's _LANG.<other> fetcher).

Normative: SCHEMA.md §Resolution semantics.

Cross-language fetch (rung 3) is the rare case: a dataset whose bytes can be produced only by a fetcher in another language. The running tool delegates (mechanism implementation-defined; the Python CLI is the reference peer), controlled by delegate / --delegate. Loading never delegates — a live object can't cross a process boundary.

Normative: SCHEMA.md §Cross-language fetch.