A definition names no host path for its own data

Twenty-eight modules' data directories are placed: the root as place ".", a sub-directory named by
its id, and every host-side reference — binds, secrets, own secrets, grants, receives, file paths,
mounts, env-files — as ${dir:<id>}. Resolved on the default root every path is the one the manifest
named before, which the controller's TestPlacedDirectoriesKeepTheirPaths proves over both checkouts;
so no data moves and no machine sees a change. Five directories whose id is not their last segment
keep their path as a placement (novox/hq issue 119, ADR 0112, design 27).

modules/model-usage/module.json

@@ -14,10 +14,10 @@
     }
   },
   "binds": {
-    "postgres-database": "/var/lib/model-usage/database.json"
+    "postgres-database": "${dir:state}/database.json"
   },
   "secrets": {
-    "postgres-database": "/var/lib/model-usage/database.secret"
+    "postgres-database": "${dir:state}/database.secret"
   },
   "consumes": [
     "*.usage.*"
@@ -35,13 +35,13 @@
     {
       "id": "state",
       "type": "directory",
-      "path": "/var/lib/model-usage",
-      "mode": "0700"
+      "mode": "0700",
+      "place": "."
     },
     {
       "id": "database-url",
       "type": "file",
-      "path": "/var/lib/model-usage/database.url",
+      "path": "${dir:state}/database.url",
       "mode": "0600",
       "content": "postgresql://${bound:postgres-database:as}:${secret:postgres-database}@${bound:postgres-database:at}:${bound:postgres-database:port}/${bound:postgres-database:as}\n"
     },
@@ -53,8 +53,8 @@
       "network": "host",
       "volumes": [
         "/var/lib/mesh/model-usage/broker:/run/secrets/broker:ro",
-        "/var/lib/model-usage:/run/state",
-        "/var/lib/model-usage/database.url:/run/secrets/database-url:ro"
+        "${dir:state}:/run/state",
+        "${dir:state}/database.url:/run/secrets/database-url:ro"
       ],
       "env": {
         "MESH_BROKER_FILE": "/run/secrets/broker",