Render for a target cluster

Charts often branch on .Capabilities.KubeVersion or .Capabilities.APIVersions. A preview should describe the target cluster, not whichever machine happens to run the preview service.

Supply capabilities explicitly

var renderer = new HelmTemplateRenderer(
    chart,
    releaseName: "preview",
    releaseNamespace: "platform",
    values: values,
    kubeVersion: "1.30.0",
    apiVersions:
    [
        "monitoring.coreos.com/v1",
        "policy/v1"
    ],
    isUpgrade: false);

var manifests = renderer.Render();
var notes = renderer.RenderNotes();

kubeVersion determines the version exposed to .Capabilities.KubeVersion. apiVersions extends .Capabilities.APIVersions with APIs that are present on the target, including CRDs. Set isUpgrade when the template must see .Release.IsUpgrade rather than .Release.IsInstall.

What the renderer gives a template

Template object	Comes from
.Values	The dictionary returned by HelmValues.BuildAsync.
.Chart	Chart.yaml metadata and chart dependencies.
.Release	The release name, namespace, revision, service, and install/upgrade state passed to the renderer.
.Capabilities	The Kubernetes version and known API versions.
.Files	Files bundled in the chart, excluding templates.
.Template	The current template name and base path.

Named templates, include, tpl, required, .Files, and the implemented Helm/Sprig functions are evaluated in-process. The function matrix is the authority for individual helpers; do not assume a helper is present because another Helm environment has it.

Keep manifests and notes separate

NOTES.txt is information for a person after a release. It is intentionally returned by RenderNotes() instead of being mixed into Kubernetes YAML. Store or display it beside a preview, but never pass it to a manifest applier.

For high-level template operations, HelmTemplateRequest provides KubeVersion, ApiVersions, and IsUpgrade at the client boundary. Render notes separately when needed; template output does not include CRDs from a chart's crds/ directory. See Install and upgrade releases for the mutation path.