+With the additional `ready/transient-recentchanges` branch, new recent
+changes go in the transient underlay; I tested this manually.
+
+Not done yet (in that branch, at least):
+
+* `remove` can't remove transient pages: this turns out to be harder than
+ I'd hoped, because I don't want to introduce a vulnerability in the
+ non-regular-file detection, so I'd rather defer that.
+
+ > Hmm, I'd at least want that to be dealt with before this was used
+ > by default for autoindex or tag. --[[Joey]]
+
+ >> I'll try to work out which of the checks are required for security
+ >> and which are just nice-to-have, but I'd appreciate any pointers
+ >> you could give. Note that my branch wasn't meant to enable either
+ >> by default, and now hopefully doesn't. --[[smcv]]
+
+* Transient tags that don't match any pages aren't deleted: I'm not sure
+ that that's a good idea anyway, though. Similarly, transient autoindexes
+ of directories that become empty aren't deleted.
+
+ > Doesn't seem necessary, or really desirable to do that. --[[Joey]]
+
+ >> Good, that was my inclination too. --s
+
+* In my `untested/transient` branch, new aggregated files go in the
+ transient underlay too (they'll naturally migrate over time). I haven't
+ tested this yet, it's just a proof-of-concept.
+
+ > Now renamed to `ready/transient-aggregate`; it does seem to work fine.
+ > --s
+
+> I can confirm that the behavior of autoindex, at least, is excellent.
+> Haven't tried tag. Joey, can you merge transient and autoindex? --JoeRayhawk
+
+>> Here are some other things I'd like to think about first: --[[Joey]]
+>>
+>> * There's a FIXME in autoindex.
+>>
+>> > Right, the extra logic for preventing autoindex pages from being
+>> > re-created. This is taking a while, so I'm going to leave out the
+>> > autoindex part for the moment. The FIXME is only relevant
+>> > because I tried to solve
+>> > [[todo/autoindex should use add__95__autofile]] first, but
+>> > strictly speaking, that's an orthogonal change. --s
+
+>> * Suggest making recentchanges unlink the transient page
+>> first, and only unlink from the old location if it wasn't
+>> in the transient location. Ok, it only saves 1 syscall :)
+>>
+>> > Is an unlink() really that expensive? But, OK, fixed in the
+>> > `ready/transient-recentchanges` branch. --s
+
+>> >> It's not, but it's easy. :) --[[Joey]]
+
+>> * Similarly it's a bit worrying for performance that it
+>> needs to pull in and use `Cwd` on every ikiwiki startup now.
+>> I really don't see the need; `wikistatedir` should
+>> mostly be absolute, and ikiwiki should not chdir in ways
+>> that break it anyway.
+>>
+>> > The reason to make it absolute is that relative underlays
+>> > are interpreted as relative to the base underlay directory,
+>> > not the cwd, by `add_underlay`.
+>> >
+>> > The updated `ready/transient-only` branch only loads `Cwd` if
+>> > the path is relative; an extra commit on branch
+>> > `smcv/transient-relative` goes behind `add_underlay`'s
+>> > back to allow use of a cwd-relative underlay. Which direction
+>> > would you prefer?
+>> >
+>> > I note in passing that [[plugins/autoindex]] and `IkiWiki::Render`
+>> > both need to use `Cwd` and `File::Find` on every refresh, so
+>> > there's only any point in avoiding `Cwd` for runs that don't
+>> > actually refresh, like simple uses of the CGI. --s
+
+>> >> Oh, right, I'd forgotten about the horrificness of File::Find
+>> >> that required a chdir for security. Ugh. Can we just avoid
+>> >> it for those simple cases then? (demand-calculate wikistatedir)
+>> >> --[[Joey]]
+
+>> >>> The reason that transientdir needs to be absolute is that it's
+>> >>> added as an underlay.
+>> >>>
+>> >>> We could avoid using `Cwd` by taking the extra commit from either
+>> >>> `smcv/transient-relative` or `smcv/transient-relative-api`;
+>> >>> your choice. I'd personally go for the latter.
+>> >>>
+>> >>> According to git grep, [[plugins/po]] already wants to look at
+>> >>> the underlaydirs in its checkconfig hook, so I don't think
+>> >>> delaying calculation of the underlaydir is viable. (I also noticed
+>> >>> a bug,
+>> >>> [[bugs/po:_might_not_add_translated_versions_of_all_underlays]].)
+>> >>>
+>> >>> `underlaydirs` certainly needs to have been calculated by the
+>> >>> time `refresh` hooks finish, so `find_src_files` can use it. --s