Cache images are not pulled from the registry

TL;DR

Fix: Maintainer iloveitaly (building on community fix PR #595 from mvanhorn plus review from mabadir): fixed the frontend import cache and added cache import/export support to the railpack build command, included in the next release.

The error

Using Railpack locally with BuildKit (`docker buildx build ... --build-arg BUILDKIT_SYNTAX=...` with a local registry): cache images are pushed after the build but never pulled before it, so every build is cold. `frontend.go`'s `Build()` never set `CacheImports` on its internal `client.Solve()` call.

Fix

1. Maintainer iloveitaly (building on community fix PR #595 from mvanhorn plus review from mabadir): fixed the frontend import cache and added cache import/export support to the railpack build command, included in the next release.

Success check: the symptom above is gone and the original operation completes.

When to use

• You hit this exact symptom in railpack.
• You want the verified fix without digging through the thread.

When not to use

• A different error in railpack, even a similar-looking one.
• General railpack setup or credential questions.

Compatibility

• Railpack (railwayapp/railpack)

Variant phrasings

• How to fix "cache images are not pulled from the registry" in railpack
• railpack: cache images are not pulled from the registry

Source

• https://github.com/railwayapp/railpack/issues/557

In gh:railwayapp/railpack#557 (https://github.com/railwayapp/railpack/issues/557), the question was: Using Railpack locally with BuildKit (docker buildx build ... --build-arg BUILDKIT_SYNTAX=... with a local registry): cache images are pushed after the build but never pulled before it, so every build is cold. The verified resolution: Maintainer iloveitaly (building on community fix PR #595 from mvanhorn plus review from mabadir): fixed the frontend import cache and added cache import/export support to the railpack build command, included in the next release.