[PLAT-5019] Split multi-arch php-laravel builds across native runners

[bbooth]

Jira

https://revolutionparts.atlassian.net/browse/PLAT-5019

Summary

• When platforms includes both linux/amd64 and linux/arm64, build each architecture on a native GitHub Actions runner in parallel instead of QEMU on a single amd64 runner
• Push per-arch tags (e.g. cli-v0.24.0-amd64, cli-v0.24.0-arm64) with per-arch registry cache keys (buildcache-cli-amd64, buildcache-cli-arm64)
• Merge into final multi-arch tags via docker buildx imagetools create (cli-TAG, cli-latest, etc.)
• Single-platform builds (linux/amd64 default) unchanged

Motivation

Listings merge-main multi-arch CLI builds took ~62 minutes because arm64 PHP extension compilation ran under QEMU on ubuntu-latest. Native arm64 runners should cut that to roughly the slowest single-arch build.

Pipeline (after this change)

Example: Listings merge-main (CLI-only multi-arch).

flowchart TB
  subgraph listings["listings — Merge Main Workflow"]
    tag["Calculate Build Tag<br/>ubuntu-latest · ~9s"]
    tag --> build["build-and-push-images<br/>calls encodium/.github<br/>php-laravel-build-push.yaml"]
    build --> prerelease["Prerelease + GH release"]
    build --> deploy["Deploy to staging EKS"]
  end

  subgraph shared["encodium/.github — php-laravel-build-push.yaml"]
    direction TB

    subgraph cli_amd64["Build + Push CLI Image (amd64)"]
      direction TB
      a1["ubuntu-latest"]
      a2["composer install + artisan cache"]
      a3["docker buildx push<br/>platform: linux/amd64"]
      a4["tag: cli-vX.Y.Z-amd64<br/>cache: buildcache-cli-amd64"]
      a1 --> a2 --> a3 --> a4
    end

    subgraph cli_arm64["Build + Push CLI Image (arm64)"]
      direction TB
      b1["ubuntu-24.04-arm<br/>native Graviton runner"]
      b2["composer install + artisan cache"]
      b3["docker buildx push<br/>platform: linux/arm64"]
      b4["tag: cli-vX.Y.Z-arm64<br/>cache: buildcache-cli-arm64"]
      b1 --> b2 --> b3 --> b4
    end

    merge["Merge CLI Image Manifest<br/>ubuntu-latest"]
    merge_step["docker buildx imagetools create<br/>→ cli-vX.Y.Z + cli-latest<br/>multi-arch manifest"]

    build --> cli_amd64
    build --> cli_arm64
    cli_amd64 --> merge
    cli_arm64 --> merge
    merge --> merge_step
  end

  merge_step --> ghcr["GHCR<br/>ghcr.io/encodium/listings:cli-TAG"]

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Before vs after (CLI image build)

flowchart LR
  subgraph before["Before PLAT-5019"]
    direction TB
    old["ubuntu-latest only"]
    qemu["Single buildx job<br/>platforms: amd64 + arm64"]
    qemu_arm["arm64 layers via QEMU<br/>~59 min PHP ext compile"]
    old --> qemu --> qemu_arm
  end

  subgraph after["After PLAT-5019"]
    direction TB
    par["Parallel native builds"]
    amd["amd64 · ubuntu-latest · ~36s"]
    arm["arm64 · ubuntu-24.04-arm · native"]
    m["imagetools merge · ~30s"]
    par --> amd
    par --> arm
    amd --> m
    arm --> m
  end

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When all three image types are enabled (app + webserver + CLI), each image type follows the same pattern: 2 parallel arch jobs + 1 merge job → final tags (TAG/latest, webserver-TAG/webserver-latest, cli-TAG/cli-latest). Those three families still run in parallel with each other.

Test plan

• Merge this PR
• Trigger Listings merge-main (or wait for next main push) and confirm:
  • Parallel amd64 + arm64 CLI build jobs on correct runners
  • Final cli-TAG manifest lists both architectures
  • Total image build time < 15 min with warm per-arch cache