Include AF container in pathauto URL
After several hours, and help from the user spovlot in #drupal-support, we have a working answer for D7:

(edit: this has been tidied up some more!)

Pattern for all forum topic paths:

forum/[node:taxonomy-forums:parents:join-path]/[node:taxonomy-forums:name]/[node:title]

combined with

Pattern for forum and forum containers:

forum/[term:parents:join-path]/[term:name]

This gives a result of:

/forum/container/sub-forum/title-of-a-post

Note that:

/forum is the name of the forum (i.e. no a forum, but a description)
Any number of containers and sub-forums will work. (forum/container/sub-a/sub-b/title-of-a-post)

Hope it helps!