For resume problems, the handbook talks about screwing around with sysctl and about removing modules, but I have two thinkpads-a very common case-where the problem was that I had failed to _load_ the i915kms module.
Knowing what to look for now, I see hints that resuming without kms awareness can’t work. At least with vt. If so, that should be mentioned.
For that matter, not even the section on X really spells out that you get the vesa driver by default and will have to get the more specific driver yourself.