A parsed pipe query: a source plus an ordered list of stages.
Returned by EctoQueryParser.parse_pipe/1 and accepted by
EctoQueryParser.build_pipe/2. The :source is one of:
{:table, name, pos}— a table reference, optionally schema-qualified ("orders","sales.orders").{:ref, slug, pos}— an external@slugreference, resolved at build time via the:resolve_sourceoption.
Callers that need to validate the table a query addresses (e.g. against a
catalog of exposed tables) should parse first, inspect :source, and only
then build with the field spec for that table.
Stage tuples (:stages) and the pos maps (%{line: l, column: c, offset: o}, all referring to the token's start) are considered
implementation detail; their shape may change between minor versions.