[6/n] [reconfigurator-cli] allow loading up an example system

[sunshowers]

Add a new command to the reconfigurator CLI, load-example, that conjures up
an example system. This allows for really easy setup, both interactively and
in automated tests. Plus, having everything be seeded is really nice for
reproducibility.

Depends on:

• [3/n] [reconfigurator-cli] drop dependency on reconfigurator-execution #6783
• [4/n] [reconfigurator] more control over ExampleSystem zone allocation #6785
• [5/n] [test-utils] turn redactor into the builder pattern #6786

[jgallagher]

Looks great!

[davepacheco]

Nice. Thanks. My suggestions here are mostly around clarifying naming and comments.

[davepacheco]

Can we give this a more descriptive name, like maybe clear or wipe?

When you say "reset the REPL" I think we're talking about terminal settings or something. What we're doing here is wiping all the in-memory state that describes the underlying system and making it match what you would get if you started the program again, right?

[sunshowers]

Hah, good point re resetting terminal settings, I was only thinking about reset in the sense of a factory reset.

[sunshowers]

Changed this to "wipe".

[davepacheco]

This makes sense but I wonder if we can give more explicit instruction to somebody that's adding a new field? How do they know which category it's in?

All of this has me wondering if we want to separate out these pieces into a separate object that we replace wholesale when needed...but I don't have a concrete suggestion at this point. We can go with this and see how it goes.

[sunshowers]

Yeah thinking about this, maybe we can introduce notions of a "system reset" (only system, not policy), a "policy reset", and a "full reset" (system and policy). Then to load an example, you'd need to do a system reset but not a policy reset.

[sunshowers]

I started pulling this thread and it got out of hand a bit:

Cargo.lock                                                   |   16 +
Cargo.toml                                                   |    1 +
dev-tools/reconfigurator-cli/Cargo.toml                      |    3 +
dev-tools/reconfigurator-cli/src/dispatch.rs                 |   74 +++
dev-tools/reconfigurator-cli/src/lib.rs                      |   12 +
dev-tools/reconfigurator-cli/src/main.rs                     | 1310 +-------------------------------------------------
dev-tools/reconfigurator-cli/src/repl.rs                     | 1246 +++++++++++++++++++++++++++++++++++++++++++++++
dev-tools/reconfigurator-cli/src/rng.rs                      |  108 +++++
dev-tools/reconfigurator-cli/src/sim.rs                      |  346 +++++++++++++
dev-tools/reconfigurator-cli/tests/input/cmds-example.txt    |   26 +
dev-tools/reconfigurator-cli/tests/output/cmd-example-stderr |    0
dev-tools/reconfigurator-cli/tests/output/cmd-example-stdout |  526 ++++++++++++++++++++
dev-tools/reconfigurator-cli/tests/test_basic.rs             |   15 +
nexus/reconfigurator/planning/src/example.rs                 |    2 +-
nexus/reconfigurator/planning/src/system.rs                  |   12 +-
nexus/types/src/deployment/execution/dns.rs                  |    4 +-
16 files changed, 2390 insertions(+), 1311 deletions(-)

I'm going to tackle this in a separate followup PR.