+**Root cause.** When the workflow was migrated from Docker to Podman in `ab22744`, the `docker/setup-qemu-action` step was removed on the assumption that pre-built binaries no longer required cross-compilation. They don't — but every `RUN` line in `Containerfile` (notably `apk add ca-certificates`) still has to execute under the target architecture. On the `amd64` runner, building the `arm64` variant therefore needs QEMU user-mode emulation registered with `binfmt_misc`. Without it, `podman build --platform linux/arm64` died with `exec /bin/sh: Exec format error`, the `arm64` image was never created, `podman manifest add` then failed, no manifest was pushed, and `cosign sign` finally failed with "Could not resolve digest". The two upstream `make` failures were not surfaced as red steps because `make ... | tee $GITHUB_STEP_SUMMARY` runs under bash without `pipefail`, so `tee`'s exit 0 masked the make exit 1.
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