nextjs_standalone_build npm deps not exec-configured, breaking cross-platform image builds with js_image_layer on macOS

[miraziz-taifin]

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Rules version: 3.0.3
Bazel version: 9.1.0 (Bzlmod)
Platform: macOS (darwin/amd64) building a linux/amd64 OCI image
Note: This report was generated by an LLM; I don't fully understand the breakage but the result is a pain point in our dev flow

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Problem

When js_image_layer is applied to a nextjs_standalone_server target with a linux platform transition, the transition cascades transitively to nextjs_standalone_build. The next build action runs on the macOS exec platform but its npm inputs — including @next/swc-* — are now selected for the linux target platform. The linux SWC binary cannot execute on macOS, so Next.js attempts a live download via pnpm config get registry, which fails because pnpm is not in the sandboxed action PATH.

Reproduction

MODULE.bazel

bazel_dep(name = "rules_oci", version = "2.3.0")
  oci = use_extension("@rules_oci//oci:extensions.bzl", "oci")                                                                                                                                                     
  oci.pull(name = "node24_slim", image = "docker.io/library/node",                                                                                                                                                 
           digest = "sha256:...", platforms = ["linux/amd64"])                                                                                                                                                     
  use_repo(oci, "node24_slim", "node24_slim_linux_amd64")

BUILD.bazel

  nextjs_standalone_build(name = "standalone", ...)                                                                                                                                                                
  nextjs_standalone_server(name = "server", app = ":standalone", ...)
                                                                                                                                                                                                                   
  js_image_layer(                                                                                                                                                                                                  
      name = "server_layers",                                                                                                                                                                                      
      binary = ":server",                                                                                                                                                                                          
      root = "/app",                                        
      platform = ":linux_amd64",   # triggers the cascading transition                                                                                                                                             
  )                                                                                                                                                                                                                
                                                                                                                                                                                                                   
  bazel build //apps/web:server_layers                                                                                                                                                                             
  # Error: /bin/sh: pnpm: command not found                 
  # (next build tried to download the darwin SWC binary because linux SWC can't execute)                                                                                                                           

Root cause

nextjs_standalone_build feeds npm packages to next build as target-configured deps. When a downstream platform transition flips the target platform to linux, those deps resolve to linux npm packages. Because next build is a Bazel action that executes on the exec platform (macOS), it requires exec-platform npm packages — particularly the SWC native binary. The action and its tool requirements are split across configurations.

Expected behaviour

js_image_layer on macOS targeting linux/amd64 should produce a valid linux image. The next build action should always use exec-platform npm packages (specifically SWC) regardless of the downstream target platform, while the packaged runfiles in the image layers use target-platform packages.

Suggested fix

In nextjs_standalone_build (or the underlying js_run_binary/action), mark the npm dep attributes that provide build-time tooling (SWC, webpack, etc.) with cfg = "exec" so they always resolve to the host platform. The build output (.next/, server.js) is platform-neutral JS and can flow through downstream target transitions unchanged.