Method: identify the exact context your input lands in, then craft the payload that breaks OUT of that context. Prove execution by making your injected JavaScript call /m03/api/solve/s_comment (e.g. with fetch()). No external collector needed. Server-rendered sinks also auto-mark once a value that would run is reflected/stored here.
Whatever you post is saved and shown to anyone who opens this page next - no per-request reflection needed. The payload persists until the pod restarts.