You told it not to render HTML but plain text.

# Nope -> 'Content-Type' => 'text/plain; charset=UTF-8'

'Content-Type' => 'text/html; charset=utf-8'
# ^^^ Yep
[download]

I got tricked by my mind

One of the best debugging techniques is to go away and do something completely different before coming back to your problem. If you're obsessing on something you can easily get tunnel vision that resetting your focus can clear up.

The next best is to get someone else to look at your problem because they'll also be coming at things fresh. Only problem is that you'll then probably feel a bit silly when they do point out the glaringly obvious you've missed for however long.

The cake is a lie.
The cake is a lie.
The cake is a lie.