Format output filled_by: agent versus projection, exact URLs

A Format run reports filled_by as agent or projection. With agent, the run itself submits the object through a tool, with the full context of the work. With projection, Sume falls back to a strict json_schema call at temperature 0 that sees only the media the run generated plus the first 8000 characters of its closing text. It does not see your input, so a field that depends on input data is a field projection will get wrong or leave null.

Whichever path fills it, media URLs are gated by exact string match against files the run actually generated, and duration_ms is checked within 10 percent.

Agent versus projection

Design for the weaker path

Keep schema fields answerable from generated media and the closing text. If a value comes from your own input, echo it back in your code rather than asking the schema for it.