envdir program is missing

Current Behavior

https://github.com/nextstrain/conda-base/blob/19bf02db4435cbb22a38c375fa3696a742598b82/src/recipe.yaml#L52

$ nextstrain shell --conda . <<<'type envdir'
Entering the Nextstrain runtime (conda)

Run the command "exit" to leave the runtime.

bash: line 1: type: envdir: not found

Expected behavior

The envdir program is available, like in the Docker runtime.

$ nextstrain shell --docker . <<<'type envdir'
Entering the Nextstrain runtime (docker)

Mapped volumes:
  /nextstrain/build is from /home/tom/nextstrain/.github

Run the command "exit" to leave the runtime.

envdir is /usr/local/bin/envdir

Possible solution

AFAICT, there's no Conda packaging of any envdir program. I checked for:

the Python envdir distribution that provides the version we use elsewhere
daemontools, which provides the original envdir
s6, which provides an s6-envdir program

We could create (and maintain) the Conda packaging of one of these; probably writing a conda-forge recipe for the Python envdir makes most sense there.

Or we could provide our own port of envdir as part of this nextstrain-base package itself. One option there would be the envdir I use day-to-day: my own port (in Perl). The advantage is this is less maintenance overhead, but the disadvantage is it doesn't also provide the Python envdir module like our other runtimes. I don't think we currently use that, but I guess we might?

nextstrain / conda-base