Function write_jsonl_single 

pub fn write_jsonl_single(
    source: &dyn ExportSource,
    rules: &[RuleDef],
    dest: &Path,
) -> Result<ExportStats, CliError>

Write one file, <dest>/graph.jsonl: every node, then every edge, then every rule, each line an object whose "type" is node, edge or rule.

{"type":"node","key":"alice","label":"Person","age":30}
{"type":"edge","edge_type":"KNOWS","src":"alice","dst":"bob","derived":false,"rule":null}
{"type":"rule","rule":{"name":"same_city",...}}

A property named type is written in the node’s $props object. mushroomdb import --jsonl reads it, a file or standard input, in this order: an edge must come after the nodes it joins.