The pinned URL pattern (https://caido.download/releases/v<X>/caido-cli-v<X>-linux-<arch>.tar.gz)
is canonical — it's published by api.caido.io/releases/latest. HEAD requests
return 404 because the upstream R2 bucket only honors GET-with-redirect, but
the wget call in the Dockerfile uses GET so the original URL was never
actually broken — it was just stale.
Switch to an ARG so future bumps are a single --build-arg override.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>