Compose interpolates the top-level .env, so a password containing "$fP" was
read as the variable $fP and replaced with an empty string — hence the
repeated "The \"fP\" variable is not set" warnings on every compose command.
The env_file templates are not interpolated, so c2-core kept the literal
password while mosquitto's entrypoint received the mangled one. The two sides
disagreed and c2-core could not authenticate to the broker. Escaping $ as $$
here (and only here) makes compose collapse it back to the real value.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Logan Cusano
971ab74d44