i3status-rust, docker-compose: each module declares the packages it needs (issue 628)

i3status-rust left pacman-contrib to the pacman module because two modules declaring one package was once refused; ADR 0303 allows it, so the bar declares what its update block runs. docker-compose's README said the package goes with the module, which the node-engine never does.

modules/docker-compose/README.md

@@ -19,8 +19,9 @@ runtime is missing or unreachable rather than an empty list.
 
 - **An owner for a package both workstations already carry.** On both, `docker-compose` 5.5.0 is
   installed explicitly by hand, as the plugin in `/usr/lib/docker/cli-plugins`. Assigning the module
-  changes nothing on disk; from then on the package is the mesh's, upgraded with the machine and
-  given back when the module goes.
+  changes nothing on disk; from then on the mesh says the package is needed, and it is upgraded with
+  the machine. Unassigning the module leaves the package installed: the node-engine never removes a
+  package a declaration stopped naming (novox/hq ADR 0303).
 - **The projects become visible from the mesh** without a shell on the machine: which are running,
   where their files are, their containers, logs and rendered configuration.
 - **No account-level copy of the plugin** exists on either workstation (`~/.docker/cli-plugins` is

modules/i3status-rust/README.md

@@ -2,7 +2,7 @@
 
 The bars as a module (novox/hq ADR 0208, research 026/05).
 
-- Installs `i3status-rust`. The update block's `checkupdates` comes from `pacman-contrib`, which the `pacman` module installs on every node; two modules declaring one package is refused at composition.
+- Installs `i3status-rust`, and `pacman-contrib` for the update block's `checkupdates`. The `pacman` module declares `pacman-contrib` too; several modules may declare one package (novox/hq ADR 0303), so each declares what it needs.
   Claims the mesh's `node-bar` seat (no verbs yet, ADR 0208 §2) and renders the blocks other modules
   contribute to it (ADR 0255, below). Requires `x11-display` on its own
   machine: its bars are i3bar's.

modules/i3status-rust/module.json

@@ -35,6 +35,11 @@
       "type": "package",
       "package": "i3status-rust"
     },
+    {
+      "id": "updates",
+      "type": "package",
+      "package": "pacman-contrib"
+    },
     {
       "id": "configuration-dir",
       "type": "directory",