fix: update buildkit client image and add oci-mediatypes to cache export

[vigneshrajsb]

Problem

Three root causes were identified in the BuildKit-based native build pipeline:

1. gRPC GOAWAY errors (client/server version mismatch) — The buildctl client image was pinned to moby/buildkit:v0.12.0 while the BuildKit daemon running in the cluster is on a significantly newer version. gRPC GOAWAY frames are sent by the server when the client is too old to communicate correctly, causing builds to fail mid-stream.

2. 30s cache manifest import delays — Without oci-mediatypes=true on --export-cache, the cache manifest is written in Docker schema v2 format. On import, the registry returns a non-OCI manifest, which triggers a slow fallback path in BuildKit before it can locate and use the cached layers. This adds a consistent ~30s penalty to every build.

3. Stale client preventing future BuildKit upgrades — Keeping the client image at v0.12.0 makes it increasingly difficult to adopt new BuildKit daemon features or upgrade the daemon without breaking the client.

Changes

• src/server/lib/nativeBuild/engines.ts
  • Upgraded buildctl client image from moby/buildkit:v0.12.0 to moby/buildkit:v0.21.0 to align client and server versions and eliminate gRPC GOAWAY errors.
  • Added oci-mediatypes=true to the --export-cache flag so cache manifests are written in OCI format, removing the 30s fallback delay on cache import.

Test plan

• Trigger a native build and confirm no gRPC GOAWAY errors in build logs
• Confirm cache import completes in under 5s (previously ~30s) on a warm cache build
• Confirm cache export completes successfully and produces an OCI-format manifest in the registry