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/showcase/module.json

@@ -20,10 +20,10 @@
     "postgres-database"
   ],
   "binds": {
-    "postgres-database": "/var/lib/showcase/database.json"
+    "postgres-database": "${dir:state}/database.json"
   },
   "secrets": {
-    "postgres-database": "/var/lib/showcase/database.secret"
+    "postgres-database": "${dir:state}/database.secret"
   },
   "own-secrets": {
     "broker": "/var/lib/mesh/showcase/broker"
@@ -100,13 +100,13 @@
     {
       "id": "state",
       "type": "directory",
-      "path": "/var/lib/showcase",
-      "mode": "0755"
+      "mode": "0755",
+      "place": "."
     },
     {
       "id": "settings",
       "type": "file",
-      "path": "/var/lib/showcase/showcase.env",
+      "path": "${dir:state}/showcase.env",
       "mode": "0600",
       "content": "SHOWCASE_GREETING=hello\nSHOWCASE_EVERY_SECONDS=30\nSHOWCASE_STATE=/var/lib/showcase\nSHOWCASE_DATABASE=${bound:postgres-database:at}\nSHOWCASE_LISTEN=${port:8080}\n"
     },
@@ -137,7 +137,7 @@
       ],
       "run-once": true,
       "env-file": [
-        "/var/lib/showcase/showcase.env"
+        "${dir:state}/showcase.env"
       ]
     },
     {
@@ -151,7 +151,7 @@
       ],
       "user": "showcase",
       "env-file": [
-        "/var/lib/showcase/showcase.env"
+        "${dir:state}/showcase.env"
       ],
       "restart-on": [
         "settings"
@@ -168,7 +168,7 @@
       ],
       "schedule": "0 3 * * *",
       "env-file": [
-        "/var/lib/showcase/showcase.env"
+        "${dir:state}/showcase.env"
       ]
     },
     {