Function build_tunnel_closed 

pub fn build_tunnel_closed(input: TunnelClosedInput<'_>) -> TunnelClosedJson

Builds the tunnel_closed payload without writing it anywhere.

The whole event — reason, forwards_served, capacity_waits, ok — used to be constructed inside the printer, so nothing could inspect it. The 0.5.4 audit found the three field names appearing in exactly one place outside the emitter: a documentation test asserting the CHANGELOG mentions them. Deleting the emission would not have turned the suite red, which is the same failure mode G-QA-R01 was written to stop.