Easy, efficient, multiarch - can I pick all 3?

[shish]

I'm currently doing multi-arch builds with

          platforms: |
            linux/amd64
            linux/arm64

and this works, but the x86 build takes 45 seconds and the arm build takes 25 minutes, presumably due to being run inside qemu.

I feel like it should be possible to run the x86 build on an x86 runner, the arm build on an arm runner, and then combine the two results (in a third workflow that depends on the first two) -- but my google-fu is failing to find anybody who's done this before, let alone documented the process, let alone packaged the steps into some re-usable Actions. Has anybody done this / have any hints?

[crazy-max]

We have started to work on a reusable workflow to distribute builds across runners: #1321

[polarathene]

Has anybody done this / have any hints?

I have prior to native ARM runners. I used QEMU but it's probably not that different from using the native ARM runner now available.

My approach was to have a separate build job for each, and a third that used build-push-action to publish. It just brings in the cache of each separate build job.

The more complex way is the manifest merging which I usually see relying on something other than cache (which does risk eviction that could trigger a full build again).

The reusable workflow linked doesn't feel like the right approach to me 😅 (at least the way it's currently done, but I understand that's due to glue for supporting a wider audience)