Application stages are the rows that make up a candidate's stage history on an application — one row per interview stage the application has occupied, with entered_at and exited_at timestamps. An application_stage is the join between an application and a job_interview_stage; the row with exited_at null (and current: true) is the candidate's current stage on that application. Filter with application_ids to retrieve the stage history for specific applications, or job_interview_stage_ids to find every application that has touched a given stage. This endpoint is the canonical source for stage-history reporting; partner BI integrations typically treat it as the fact table.