chain commands, and let a project refine a catalogue stack

myos build up logs host/fabio runs the three in order and stops at the first
failure, the way make build up logs STACK=host/fabio did. Leading words that
name commands are commands; the first word that is not one starts the stacks.

A stack found in several directories of the stack path is now merged rather
than shadowed, least specific first, so a project drops
stack/postgres/postgres.local.yml next to the catalogue's postgres.yml and
refines it. Settings hooks follow the same order, so a project can redefine a
default the catalogue ships. Neither engine did this before: the project
directory simply hid the catalogue one.

An unknown command now says so and suggests the command to type, instead of
printing the whole usage.

skills/myos/SKILL.md

@@ -48,6 +48,9 @@ myos down <stack>             # remove the containers
 
 A reference is `[<group>/]<name>[:<version>]`, or a path.
 
+Commands chain: `myos build up logs host/fabio` runs the three in order and
+stops at the first failure.
+
 ```sh
 myos up                    # the current directory, when it holds a compose file
 myos up host               # a group: expands to host/consul host/fabio ...
@@ -57,9 +60,13 @@ myos -C /opt/app up        # somewhere else
 myos -e master up          # in another environment
 ```
 
-Stacks are looked up along the stack path, project first:
-`./stack`, `../stack`, `~/.local/share/myos/stack`, `/usr/local/share/myos/stack`,
-`/usr/share/myos/stack`. `myos doctor` prints the resolved path.
+Stacks are looked up along the stack path: `./stack`, `../stack`,
+`~/.local/share/myos/stack`, `/usr/local/share/myos/stack`, `/usr/share/myos/stack`.
+`myos doctor` prints the resolved path.
+
+A stack found in several of them is **merged**, the project last, so a project
+adds `stack/postgres/postgres.local.yml` next to the catalogue's `postgres.yml`
+and refines it instead of replacing it. The same goes for the settings hooks.
 
 ## Three kinds of stack
 

skills/myos/references/commands.md

@@ -30,6 +30,20 @@ myos [options] <command> [stack...] [VAR=value...] [-- args...]
 | `doctor` | check the installation |
 | `version` | the myos version |
 
+## Several commands at once
+
+Commands chain, the way make targets did. Leading words that name commands are
+commands; the first word that is not one starts the list of stacks.
+
+```sh
+myos build up logs host/fabio        # like: make build up logs STACK=host/fabio
+myos up ps host
+```
+
+They run in order and stop at the first failure. A stack whose name is also a
+command name has to be given as `STACK=<name>`, otherwise it is read as a
+command.
+
 Anything after `--` goes to docker compose:
 
 ```sh
@@ -65,7 +79,8 @@ does not: a typo is an error.
 |---|---|
 | `make up STACK=host` | `myos up host` |
 | `make print-COMPOSE_FILE` | `myos env COMPOSE_FILE` |
-| `make host` | `myos up host` |
+| `make host` | `myos up host` (a bare stack name is not a command) |
+| `make build up logs STACK=host/fabio` | `myos build up logs host/fabio` |
 | `make stack-host-config` | `myos config host` |
 | `make up@master` | `myos -e master up` |
 | `make exec SERVICE=php ARGS='ls'` | `myos exec <stack> -- php ls` |

skills/myos/references/conventions.md

@@ -99,6 +99,20 @@ parsed, never sourced, so a value may contain a `#` or a `$(...)` without
 breaking anything or being executed. The make engine included `.env` as a
 makefile, where both broke.
 
+## Where a stack lives
+
+The same stack may exist in several directories of the stack path. They are all
+loaded, least specific first, so the project has the last word:
+
+```
+/usr/local/share/myos/stack/postgres/postgres.yml     the catalogue
+./stack/postgres/postgres.local.yml                   the project refines it
+./stack/postgres/postgres.sh                          and may redefine a default
+```
+
+Nothing has to be copied to change one setting: a value in the project `.env`
+already wins over any default a stack ships.
+
 ## Per-stack settings
 
 A stack keeps its own settings next to its compose files: