pub fn export_file(input: &Path, output: &Path) -> Result<(), String>Expand description
Export a JSONL session file to the specified format.
The input is a real JSONL v4 session file (header line + one mutation per
line), so it is parsed with the harness codec rather than assuming raw
Entry JSON. Only entry mutations contribute to the rendered transcript;
lane/fact/record lines are skipped (they are not conversational content).