Declare every module's data; the backup holder measures it (hq ADR 0233)

Backup lines are derived from each module's data section instead of written by hand; the holder
measures declared items, reads the array under them, and deletes a retired item only after a last
restore point; the Go providers say each held consumer's size so an empty replacement is seen.

modules/restic/module.json

@@ -15,6 +15,23 @@
   "own-secrets": {
     "repository": "${dir:state}/repository.secret"
   },
+  "data": {
+    "own": [
+      {
+        "id": "repository",
+        "path": "${dir:repository}",
+        "class": "rebuildable",
+        "backup": "none",
+        "why": "the restore points themselves: a copy of data kept elsewhere on this machine, never the only copy of anything; lost, the history goes and nothing live does"
+      },
+      {
+        "id": "state",
+        "path": "${dir:state}",
+        "class": "cache",
+        "why": "what the last nights and measurements were; the next night writes it again"
+      }
+    ]
+  },
   "resources": [
     {
       "id": "state",
@@ -34,6 +51,13 @@
       "mode": "0600",
       "content": "# What the modules on this machine back up, composed by the mesh (novox/hq to-be 43). Do not edit.\n${contribution:node-backup:backup}"
     },
+    {
+      "id": "data-declared",
+      "type": "file",
+      "path": "${dir:state}/data.conf",
+      "mode": "0600",
+      "content": "# The data the modules on this machine declare, composed by the mesh (novox/hq ADR 0233). Do not edit.\n${contribution:node-backup:data}"
+    },
     {
       "id": "tool",
       "type": "package",
@@ -61,7 +85,8 @@
           "MESH_BACKUP_DECLARED": "${dir:state}/backups.conf",
           "MESH_BACKUP_REPOSITORY": "${dir:repository}",
           "MESH_BACKUP_PASSWORD_FILE": "${dir:state}/repository.secret",
-          "MESH_BACKUP_STATE": "${dir:state}"
+          "MESH_BACKUP_STATE": "${dir:state}",
+          "MESH_BACKUP_DATA": "${dir:state}/data.conf"
         }
       }
     ]