The compat package marshals the base value into JSON to convert it into
a map[string]any, then applies the compat options, and finally
re-encodes the map into JSON.
`json.Marshal` is used for both marshalling operations. However, this
function encodes special HTML characters by default. The API responses
aren't meant to be embedded into HTML, so this behavior is not desired.
Replace `json.Marshal` with a `json.Encoder` with HTML escaping
disabled. Extra care is taken to drop the trailing LF added by
`(*json.Encoder).Encode()` (see [1]).
[1]: https://pkg.go.dev/encoding/json#Encoder.Encode
Signed-off-by: Albin Kerouanton <albinker@gmail.com>
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