Function register 

pub async fn register(
    store: &TemplateStore,
    req: RegisterRequest,
) -> CliResult<TemplateRecord>

Available on crate feature templates only.

Validate a submitted config and append it as a new template version.

Validation deliberately runs against a placeholder binding: required params have no value at registration time, so each is filled with a type-shaped stand-in and the config is then taken through the real PipelineConfig parse plus expand (matrix mode) or crate::topology::validate_topology_spec (topology mode). That checks everything structural — grammar, named templates, the matrix graph (parent/depends_on cycles, duplicate state keys), the exactly-once and write-mode gates, edge endpoints — without resolving a single secret or constructing a single connector. Node arity in topology mode is validated when the graph is built, i.e. at trigger time, because building it requires live connectors that a placeholder-bound config must not create.