Can the middle node of my Tor circuit detect if I am using a bridge and/or pluggable transport?
With Nyx¹ (formerly tor-arm) you can see the IP, fingerprint and nickname of the Tor relays that form a cirquit. Middle node can see that a bridge is used, but not whether and which pluggable transport is used from the client (Tor-Browser) to the bridge.
¹Or other tools that use Stem interpreter
I don't want to show a productive relay. Hence: Tor Nyx on a hidden service that syncs a blockchain.