Constant SUBMIT_FORMAT_KEY 

pub const SUBMIT_FORMAT_KEY: &str = "submit_format";

AgentContextView.extra key carrying a step’s declared submit format. Declared through the GH #21 meta channels (Blueprint.metas / AgentMeta.ctx / step-level $step_meta) and folded into the view at spawn time by AgentContextMiddleware. Read in two places: the HTTP submit lane (mlua-swarm-server’s resolve_submit_value, where "json" means strict parse-or-422) and Engine::fold_parse_mode_for (where SUBMIT_FORMAT_TEXT opts the step’s fold out of the default lenient container parse — see FoldParse).