docs: bring the readme up to date with the commands that exist

README.md

@@ -10,16 +10,50 @@ You will need rust installed. Clone repo and run:
 cargo install --path .
 ```
 
+## what it makes of a project
+
+`ahab status` prints the services it picked, the containers behind them, the
+credentials it would use and what the store holds, reporting whatever it cannot
+work out rather than stopping at the first thing:
+
+```
+$ ahab status
+services: db, django
+django: django (built from the project)
+	container: 0a8b19e27634
+postgres: db (postgres:18-alpine)
+	container: 189d4d395d62
+	user:      myproject
+	database:  myproject_db
+store: /home/you/.local/share/ahab/git.aflabs.org/urnik/afurnik
+	linked:    2
+	`ahab link check` lists what a sandbox can still read
+```
+
 ## seeing what it runs
 
-`-v` prints each docker command as it runs, and `--dry-run` prints the ones it
-would run without running them. Both work before or after the subcommand.
+`-v` prints each docker command as it runs, `--dry-run` prints the ones it would
+run without running them, and `-q` prints only what was asked for, dropping the
+progress along the way (compose's own progress included). All work before or
+after the subcommand.
 
 ```bash
-ahab -v django test
+ahab -v django migrate
 ahab --dry-run postgres import ./dump
+ahab -q postgres dump ./dump
 ```
 
+Nothing is written under `--dry-run`, filesystem included: `link add` and
+`django make-command` say what they would do and leave the tree alone.
+
+## exit codes
+
+- `0` — it ran and had nothing to report
+- `1` — it could not finish
+- `2` — the arguments were wrong
+- `4` — it ran fine and found something worth reporting, i.e.
+  `link check --exit-code` with anything outside the store
+
 ## shell completion
 
 `ahab completions <shell>` writes a completion script to stdout, for bash,
@@ -80,10 +114,17 @@ ahab django manage <args>            # manage.py
 ahab django makemigrations
 ahab django migrate <args>
 ahab django shell
-ahab django test
 ahab django make-command <app> <name>
 ```
 
+There is no `ahab django test`: which runner a project uses is the project's
+choice, and `manage.py test` exits 0 having collected nothing when the tests are
+written for pytest, so a wrong guess reads as a pass. Name the runner instead:
+
+```bash
+ahab django run pytest -x tests/
+```
+
 ## postgres
 
 ```bash
@@ -94,6 +135,15 @@ ahab postgres dump -F directory <d>  # pg_dump, a directory of files
 ahab postgres dump -F cluster <path> # pg_dumpall, roles and all databases
 ahab postgres dump -F plain -z <path> # any of them, gzipped
 ahab postgres import <path>          # drop, create, then restore
+ahab postgres psql <args>            # psql in the database container
+```
+
+`psql` passes its arguments through and only asks docker for a terminal when it
+has one to hand over, so both of these work:
+
+```bash
+ahab postgres psql                          # interactive
+ahab postgres psql -tAc 'select count(*) from auth_user' | wc -l
 ```
 
 The format of a dump being imported is read from the file rather than its name.
@@ -106,7 +156,8 @@ differently again: it creates its own databases and carries role statements, so
 the database is dropped but not recreated, the dump goes to `psql` connected to
 `postgres`, and it runs without `ON_ERROR_STOP` because roles that already exist
 report errors that are expected. Gzipped dumps are decompressed on the way in,
-whichever of the three they hold.
+whichever of the three they hold. A cluster that has never held the database
+yet is a valid target either way, so importing into a fresh one works.
 
 ## link
 
@@ -117,22 +168,47 @@ dangling symlink instead of the contents, while the host resolves it as before.
 ```bash
 ahab link add .env secrets/         # move out, leave symlinks behind
 ahab link restore .env              # move it back into the repository
-ahab link restore --all             # everything this repo has in the store
+ahab link restore --all             # everything this repo has linked
+ahab link list                      # what the store holds for this repository
 ahab link check                     # what a sandbox can still read
 ahab link check --porcelain         # `<code> <path>`, for scripts
+ahab link check --exit-code         # exit 4 when anything is outside the store
 ```
 
 `restore` is the inverse of `add`: the file moves out of the store and back to
 where it was, and the store keeps nothing. A second checkout linking the same
 path is left with a dangling symlink, since there is only ever one stored copy.
 
+`list` says what state each stored path is in, which `check` cannot see because
+it asks git about the repository rather than reading the store:
+
+```
+$ ahab link list
+store: /home/you/.local/share/ahab/git.aflabs.org/urnik/afurnik
+	linked:    .env
+	shadowed:  config.local.py
+	missing:   secrets/token
+```
+
+`missing` is a path whose symlink is gone, `shadowed` one that a real file took
+back; either way the stored copy is the one nobody reads.
+
+`restore --all` moves back the linked ones and says how many it left, since
+there is nothing to undo for a path whose symlink is gone.
+
+`-z` is the porcelain format for scripts that must survive any filename: entries
+end with a NUL, and the two paths of a symlink leading elsewhere are separated
+by one as well, the way `git status -z` reports a rename.
+
 The store lives under
 `${XDG_DATA_HOME:-$HOME/.local/share}/ahab/<host>/<owner>/<repo>/`, derived
-from the git `origin` remote.
+from the git `origin` remote, or `_local/<checkout>` when there is no remote to
+name it after.
 
 ## configuration
 
 Currently `ahab` respects the following environment variables.
 
 - `AHAB_LINK_ROOT`: where `ahab link` keeps its store - the same as `--store`,
-  which takes precedence, and defaults to `${XDG_DATA_HOME:-$HOME/.local/share}/ahab`
+  which takes precedence, and defaults to `${XDG_DATA_HOME:-$HOME/.local/share}/ahab`.
+  `ahab status` reads it too, so it reports the store the link commands use