Request mapping on nested routes hard to line up

Nobody has claimed this yet.

Given the following comments controller in **controller/posts/comments/controller.go**:

```go
package comments

type Controller struct {}

type Input struct {
PostID int
}

func (c *Controller) Index(in *Input) *Input {
return in
}
```

And the following request `GET /posts/10/comments`. The resulting request map from this request is:

```
{
"post_id": 10
}
```

Unfortunately, that doesn't line up with `PostID`. Either:

1. The request map would be `{ "PostID": 10 }`
2. Or the PostID field has a `json:"post_id"` struct tag.

This isn't too obvious. I think I'd like the protocol between controller and request map to be strict (e.g. matching, case-sensitive keys) to avoid multiple, valid different request maps, but this might be too cumbersome without proper validation errors (coming soon!).

Read controller/posts/comments/controller.go and trace the request mapping for GET /posts/10/comments. Compare the generated post_id key with Input.PostID, then resolve whether strict case-sensitive keys or struct tags are the intended contract. Done means the contract is explicit and the nested-route example maps consistently.

Written by the indexing model from the issue text.