# Documentation

**Only what cannot be discovered by running the tool or reading the code.**
Flags and defaults are in `atgc <command> --help`. What a command prints is
in its output. Why a dependency is vendored is in `Cargo.toml`. What changed
and when is in `git log`. What is enforced is in `prek.toml`. None of that is
repeated here, because a second copy is a second thing to be wrong.

What is left is six pages:

1. [The model](architecture.md). Tangled's shape, which is somebody else's
   system and cannot be read out of this repo. Start here; nothing else makes
   sense first.
2. [Who atgc acts as](accounts.md). Which account a command publishes under,
   how a worktree gets one of its own, and how to give several agents
   several identities.
3. [Output contracts](output.md). The five rules that hold for every command.
4. [Module layout](module-layout.md). Where code goes, and the rules that are
   not visible from the folder names.
5. [Testing](testing.md). What earns a test, and when to reach for a mock.
6. [Environment](environment.md). Every `ATGC_*` variable, including the ones
   no `--help` page names.

These are CommonMark under `docs/`, also compiled into rustdoc by
`src/docs.rs`, so a reference from prose into code is checked at build time.
`cargo docs` builds it. Code fences need a language tag and must not be
`rust`; `prek` explains why when it stops you.