Why is no template applied two levels deep?

I’m quite confused about how templates are applied. Apologies if I’m missing an obvious answer to this question somewhere.

Here are the relevant directories:

content
├── posts
│   ├── blog
│   │   ├── first_blog_post.md
│   │   └── second_blog_post.md
│   ├── code
│   │   └── first_code_post.md

Layouts:

layouts
├── _default
│   ├── list.html
│   └── single.html
├── about
│   └── single.html
├── index.html
├── partials
│   ├── categories.html
│   ├── footer.html
│   ├── ga.html
│   ├── header.html
│   ├── navbar.html
│   └── tags.html
└── posts
    └── blog
        └── list.html

When I navigate to posts/blog, nothing appears to be rendered. I would expect the layout at posts/blog/list.html to serve as the template. Failing that, I would think at least layouts/_default/list.html to be rendered.

What am I doing wrong here? Can I not do two levels deep like this?

Well, looks like I used the wrong search terms. It turns out subsections aren’t yet available. What a bummer! I am very much looking forward to when they are.

Relevant github issue

EDIT:

And just to drive home that I did a crummy job figuring this out, here is another.