# Description
This PR implements an experimental inter-job communication model,
through direct message passing, aka "mail"ing or "dm"ing:
- `job send <id>`: Sends a message the job with the given id, the root
job has id 0. Messages are stored in the recipient's "mailbox"
- `job recv`: Returns a stored message, blocks if the mailbox is empty
- `job flush`: Clear all messages from mailbox
Additionally, messages can be sent with a numeric tag, which can then be
filtered with `mail recv --tag`.
This is useful for spawning jobs and receiving messages specifically
from those jobs.
This PR is mostly a proof of concept for how inter-job communication
could look like, so people can provide feedback and suggestions
Closes #15199
May close#15220 since now jobs can access their own id.
# User-Facing Changes
Adds, `job id`, `job send`, `job recv` and `job flush` commands.
# Tests + Formatting
[X] TODO: Implement tests
[X] Consider rewriting some of the job-related tests to use this, to
make them a bit less fragile.
# After Submitting
