Function format_background_outcome 

pub fn format_background_outcome(outcome: &BackgroundOutcome) -> String

Formats a background task outcome into a text block that is fed back into the conversation.

The wording is structured as a “deferred tool result return”, clearly marking the source (task id + label) and success/failure, to prevent the model from misinterpreting it as user speech. Phase 2 will replace this with the proper ingest path using IngestSource::Background, at which point this function will be superseded by the corresponding payload.