Stack source: pre-parsed documents, or raw YAML + substitution env.
Optional
Already-parsed canonical documents (e.g. from loadStackFile).
loadStackFile
Env record for ${VAR} substitution when yaml is given (default {}).
${VAR}
yaml
{}
Raw multi-document stack YAML, parsed with parseStackDocuments.
Stack source: pre-parsed documents, or raw YAML + substitution env.