feat: implement helm pull command

[bradctrlplus]

Background

helm pull downloads a chart from a repository (HTTP or OCI) to the local filesystem, optionally untarring it. Common uses: offline installs, chart inspection, customization, CI caching. See helm pull docs.

Helm SDK action: action.NewPullWithOpts (upstream).

Acceptance criteria

• Helm.pull("repo/chart").call() downloads to current directory and returns the resulting file Path
• Builder methods: .withDestination(Path), .untar(), .withUntarDir(String), .withVersion(String)
• Repo + auth: .withRepo(String), .withUsername(String), .withPassword(String), .passCredentials(), .withRepositoryConfig(Path), .withRepositoryCache(Path)
• TLS: .withCertFile(Path), .withKeyFile(Path), .withCaFile(Path), .insecureSkipTlsVerify(), .plainHttp()
• Verification: .verify(), .withKeyring(Path)
• Versioning: .devel()
• .debug()
• Works with oci://... chart references
• Integration tests use the built-in HTTP and OCI test servers (see Tests below)

Proposed Java API

Path chartFile = Helm.pull("bitnami/nginx")
 .withVersion("15.0.0")
 .withRepo("https://charts.bitnami.com/bitnami")
 .withDestination(Paths.get("/tmp/charts"))
 .untar()
 .call();

Implementation guide

Follow AGENTS.md → "Adding a new Helm command".
Reference impl: ShowCommand + show.go — same shape (chart-keyed, repo + TLS options, uses the shared newRegistryClient helper for OCI).

Go (native/internal/helm/pull.go)

• Build config with NewCfg(&CfgOptions{...}) — do not construct action.Configuration{} directly. Every other command in the codebase goes through NewCfg; staying consistent is required for kubeconfig / settings handling.
• Build a registry.Client via the existing newRegistryClient(...) helper in registry.go:94.
• client := action.NewPullWithOpts(action.WithConfig(cfg)), then set Settings, RepoURL, Version, Username, Password, CertFile, KeyFile, CaFile, InsecureSkipTLSverify, PlainHTTP, Verify, Keyring, Devel, DestDir, Untar, UntarDir, PassCredentialsAll.
• client.Run(chart) returns (string, error) — the string is helm's CLI output (typically empty for pull). Compute the resulting file/directory path from DestDir + chart filename + version and return it as the first string returned by your helm.Pull(...) function so the Java side can parse it back to Path.

CGO bridge (native/main.go)

• Add struct PullOptions { ... } alongside other option structs.
• Add //export Pull wrapping helm.Pull(...) via runCommand(func() (string, error) { ... }). There is no result(...) helper — every other export uses runCommand.

JNA + Java

• lib/api/.../PullOptions.java: mirror the C struct field order (@Structure.FieldOrder).
• Add Result Pull(PullOptions options) to HelmLib.
• helm-java/.../PullCommand.java extends HelmCommand<Path>. call() runs the command and returns Paths.get(result.out.trim()).
• Add Helm.pull(String chart) static factory. Use HelmLibHolder.INSTANCE directly — it is the HelmLib instance, there is no .helmLib() method.

Tests

• Location: helm-java/src/test/java/com/marcnuri/helm/HelmPullTest.java.
• Start a local repo server using the low-level JNA call (the high-level builder isn't exposed) — see HelmTestServerTest for the pattern:

  final Result r = Helm.HelmLibHolder.INSTANCE.RepoServerStart(new RepoServerOptions());
  // r.out contains the URL

• For OCI, use RepoOciServerStart similarly.
• Scenario suggestions:
  • Valid: fromRepo, withVersion, withDestination (asserts file exists at expected path), withUntar (asserts directory contents), withRepoUrl, fromOciRegistry
  • Invalid: nonExistentChart, nonExistentVersion
• No KinD container needed — pull is client-only.

Contributor checklist

• Java 8 syntax only
• Apache 2.0 header (or make license)
• @author Javadoc tag
• DCO sign-off (git commit -s)
• make build-native && ./mvnw test -pl helm-java -Dtest=HelmPullTest green

References

• Helm CLI: https://helm.sh/docs/helm/helm_pull/
• Helm SDK: https://github.com/helm/helm/blob/v3.21.0/pkg/action/pull.go
• Project workflow: AGENTS.md → Adding a new Helm command
• Reference impl: ShowCommand.java + native/internal/helm/show.go
• Test infra reference: HelmTestServerTest.java