Function build_deferred_tools_section 

pub fn build_deferred_tools_section(deferred: &DeferredMcpToolSet) -> String

Build the <available-deferred-tools> section for the system prompt. Lists tool names with a one-line summary each (the first non-empty line of the description, capped) so the LLM knows what is available without consuming context window on full schemas or full docstrings. Includes an instruction block that tells the LLM to call tool_search to activate them.