Schema-driven typed decoding of raw fact rows for in-process consumers.

Argus.Pipeline.Emit produces facts as lists of string fields — the right shape for Souffle .facts files, but stringly for Elixir consumers. This module decodes those rows against Argus.Schema: each row becomes a map keyed by the schema's field names, with values decoded by field kind (numbers and labels to integers, instruction IDs to Argus.InstrId structs).

Decoding is strict: a row that doesn't match its relation's schema (wrong arity, non-numeric number, malformed instruction ID) raises — such a row can only come from a bug in an emitter or extractor, and surfacing it loudly at the decode boundary beats consumers silently dropping it. Relations not in the schema (custom extractor output) pass through undecoded.

Eventually emission itself may become typed, with stringification pushed to the .facts writer; this decoder is the compatible first step.