Function generate 

pub fn generate(
    pack_id: &str,
    agents: &BTreeMap<String, Value>,
    tool_reqs_by_ext: &BTreeMap<String, Vec<ToolSecretReq>>,
    component_reqs: &[SecretRequirementOut],
) -> Result<Option<GeneratedSetup>>

Build setup.yaml + secret-requirements.json from a pack’s agents and the resolved tool secret requirements. Returns None when there is nothing to emit. Component requirements are merged into secret-requirements.json.