# M2b task 08: `loopd serve`

**Branch:** `m2b` (run `git switch m2b`; `git status --short` must be empty, otherwise stop)
**Commit subject:** `Add the loopd serve command`

## Goal

The command that runs the harness: self-test, then the channel server. It refuses to start if the
self-test fails.

## Files

- Copy: `crates/loopd/tests/serve.rs`
- Modify: `crates/loopd/src/main.rs`, `docs/implementer-log.md`

## What `loopd serve --config <path>` does, in order

1. Load the config; on failure print `loopd: <error>` and exit 1.
2. Work out the socket path with `cfg.channel_socket()`. If a socket file is already there,
   remove it **now**, before the self-test, so that a client sees "not running" rather than
   "connection refused" while the self-test runs.
3. Run the self-test exactly as `loopd selftest` does, printing the same lines. On failure exit 1
   without binding anything.
4. Create the socket's parent directory, bind, set the socket file's mode to 0600, print
   `loopd: serving on <path>`, and call `channel::serve` with a `Context` made of the config, the
   client, `Box::new(FakeTools::new())` and `Registry::m2b()`.

`loopd selftest --config <path>` keeps working as before. Anything else prints the usage for both
commands and exits 2.

## Steps

- [ ] **1. Copy.** `git switch m2b`, then
  `cp docs/plans/M2b/files/crates/loopd/tests/serve.rs crates/loopd/tests/`
- [ ] **2. See the test fail.** `cargo test -p loopd --test serve`. Expected: all 3 fail, because
  `serve` is not a command yet.
- [ ] **3. Rewrite `main.rs`.** Keep the `selftest` command. Run `cargo fmt --all`.
- [ ] **4. See the tests pass.** `cargo test -p loopd --test serve`. Expected: `3 passed`.
- [ ] **5. Run the gate.** `make gate`. Expected last line: `gate: ok`.
- [ ] **6. Log and commit.** `git add crates/loopd docs/implementer-log.md && git commit`

## Done when

- `cargo test -p loopd --test serve` reports 3 passed; `make gate` prints `gate: ok`.

## Stop and report if

- The socket cannot be given mode 0600 with `std::fs::set_permissions`.