Reject helm template name and namespace starting with '-' - #1886

spec.template[].helmTemplate.name is passed to "helm template" as the first positional argument without validation. A value starting with '-' is parsed by helm as a flag instead of a release name, so arbitrary helm template flags can be supplied through this field, e.g. "--set-file=key=" makes helm read a file from the controller (or sidecarexec) container filesystem into the rendered manifests. The same value can also be set on a PackageInstall through the ext.packaging.carvel.dev/helm-template-name annotation.

Return an error before invoking helm when the resolved name or namespace starts with '-'. Both values come from the App spec (or the PackageInstall annotations), so they are validated at the point where the helm arguments are built, which covers both paths. Valid release names and namespaces can never start with '-', so this does not change behavior for existing valid configurations.

Changes:

1. pkg/template/helm_template.go

   • Reject name and namespace values starting with '-'

2. pkg/template/helm_template_test.go (new)

   • Add Test_HelmTemplate_NameAndNamespace covering accepted and rejected values, and verifying helm is not invoked when rejected
   • Add Test_HelmTemplate_NameIsNotParsedAsHelmFlag, which runs helm with a name of "--set-file=value=" and verifies the file content is not rendered. Without this change the file content appears in the helm output.

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