Stale build cache leads to outdated dependencies after scalingo rebuild

Goal: guarantee that every Scalingo deploy uses only the current source code and dependencies, without any stale build‑cache artifacts affecting the resulting Docker image.

Uncertainty: while the `scalingo rebuild` command is documented to discard the cached layer, the platform’s build‑cache behavior may vary between free and paid plans, and environment variables such as DATABASE_URL that are injected at container start‑up could influence which layers are considered reusable.

Questions: Does `scalingo rebuild` reliably produce a clean build on both free and paid Scalingo plans? Are there circumstances under which cached layers persist despite a rebuild command? How can a user confirm that no stale cache was used without relying on build‑log inspection?