Without --pull, the host's Docker layer cache wins: if a CVE drops in
node:20.19.0-alpine3.21 / postgres:16-alpine and the vendor re-publishes
the same tag, the runner keeps serving the cached layer until the cache
is manually cleared — a silent supply-chain blind spot.
Adding --pull to both `compose build` invocations costs a single
re-pull per run and lifts the base-image patch lag from "next host
prune" to "next nightly".
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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