Kubernetes Helm provider exposes credentials in argv

What happened:

The single-cluster Kubernetes Helm provider passes registry and chart repository passwords on the Helm command line. LoginToOCIRegistry builds helm registry login -u <user> -p <password> ..., and AddRepository builds helm repo add ... --username <user> --password <password>. That exposes credentials through process inspection tools because the secret is present in argv.

What you expected to happen:

Passwords should be provided through stdin or another non-argv channel, consistent with the safer implementation already used by the multicluster Kubernetes provider.

How to reproduce it:

1. Open pkg/app/pipedv1/plugin/kubernetes/provider/helm.go.
2. Inspect LoginToOCIRegistry and note that it appends -p and the raw password to the Helm args.
3. Inspect AddRepository and note that it appends --password and the raw password to the Helm args.
4. Compare that with pkg/app/pipedv1/plugin/kubernetes_multicluster/provider/helm.go, which already uses --password-stdin and sets cmd.Stdin.
5. Run a focused regression test with a fake Helm executable that records argv; the password currently appears in the recorded arguments.

Environment:

• piped version: current master checkout as of 2026-07-08
• control-plane version: Not applicable
• Others: Local code inspection of the Kubernetes and Kubernetes multicluster Helm providers

Summary

The single-cluster Kubernetes Helm provider leaks registry and repository credentials via process arguments.

Affected Area

pkg/app/pipedv1/plugin/kubernetes/provider/helm.go

Steps to Reproduce

1. Read LoginToOCIRegistry in pkg/app/pipedv1/plugin/kubernetes/provider/helm.go.
2. Read AddRepository in the same file.
3. Observe that passwords are appended directly into Helm argv.
4. Compare with pkg/app/pipedv1/plugin/kubernetes_multicluster/provider/helm.go.

Expected Behaviour

Passwords are passed via stdin and never appear in process arguments.

Actual Behaviour

Passwords are appended directly to Helm command arguments in the single-cluster provider.

Technical Evidence

• pkg/app/pipedv1/plugin/kubernetes/provider/helm.go currently uses -p <password> for OCI login and --password <password> for helm repo add.
• pkg/app/pipedv1/plugin/kubernetes_multicluster/provider/helm.go already uses --password-stdin and cmd.Stdin = strings.NewReader(...).

Suspected Root Cause

The single-cluster provider still uses older Helm argument handling while the multicluster provider has already moved to stdin-based credential passing.

Proposed Direction

Port the single-cluster provider to the same --password-stdin pattern and add regression tests that fail if a secret appears in recorded command arguments.

Acceptance Criteria

• No Helm password is passed as a command-line argument in the Kubernetes single-cluster provider.
• OCI registry login uses a non-argv secret channel.
• Helm repository add uses a non-argv secret channel.
• Regression tests fail if a password appears in recorded argv.

Start in pkg/app/pipedv1/plugin/kubernetes/provider/helm.go by reading LoginToOCIRegistry and AddRepository, then compare them with the multicluster provider's helm.go implementation. Run focused regression tests using a fake Helm executable that records argv. Done means registry and repository passwords use a non-argv channel and never appear in recorded arguments.