Run a follow-up action on a completed Suno job

Runs a follow-up action on a completed suno job, referenced by its job ID. Every action selects one of the parent's tracks with index (1–2) or trackId (from the parent's result.tracks[].id). extend continues the track from continueAt (seconds; defaults to the end of the track and must be less than its duration). cover re-generates the track in a new style while keeping its core melody (audio_weight 0–1 controls how closely it follows the source). add_vocals layers AI-generated vocals onto the track — prompt (the lyrics) is required; intended for instrumental parents. stems splits the track into separate vocals and instrumental audio files. Optional prompt (lyrics in custom mode, a description otherwise), title, style, and negative_tags override the inherited values. Extend, cover, and add_vocals results are fresh pairs of Suno tracks and can be acted on again; stems results are 2 plain audio files (vocals + instrumental) that accept no further actions. Returns 409 when the action is not available for the parent job.