config set wrote every value as an unquoted YAML scalar, and config.Load
reads the file through untyped YAML, so an access key 00112233 loaded as
38043 and a hostname 007 as 7.
config set now looks the key up in config.Config by the fields' yaml
tags. A string setting is tagged !!str, which the encoder quotes
wherever YAML would read a number or a boolean. Other settings stay
unquoted, so compression_level 9 is still a number. A value that is not
valid UTF-8 stays untagged: the encoder refuses it as !!str and writes
it as !!binary, which loads back unchanged.
Judgement call: the type comes from reflection over config.Config.
Quoting every value YAML would change avoids that, but would also quote
odd numbers such as compression_level 03 and make them fail to load.
Model: opus-5-5
sneak