/usr/share/subiquity/subiquity-debug is in subiquity 0.0.29.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 | #!/bin/sh
set -e
stty -echo
echo "Please press Enter to activate this console."
read REPLY
stty echo
exec bash
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