Function expand_includes 

pub fn expand_includes(
    pipeline: &mut Pipeline,
    resolved: &HashMap<String, Value>,
    allow_remote_include: bool,
) -> Result<(), String>

Expand all Include transformations in a pipeline.

For each Include { template }, the template references a source ID. The resolved source data is expected to be a YAML array of transformation objects. These are parsed and spliced into the pipeline at the include position.

Security: if allow_remote_include is false, includes referencing HTTP or NATS sources produce an error.

Recursive includes are not allowed (max depth 1). If an included fragment itself contains Include directives, expansion fails with an error.