Raise genesis's store as the postgres module's server, so the store step adopts it as it runs (hq issue 609, ADR 0338)

The bundle raised the store as mesh-store, on upstream postgres, in a docker volume; the postgres
module keeps it as postgres, on its pgvector image, in /var/lib/mesh-store owned 999:70, reading its
superuser password from a file. The store step refused, and genesis stopped at step 17 of 24.

The bundle now raises the store with the module's name, image, data directory and password file, and
every step of the bundle and the installer reaches it by that name. The refusal to raise a store over
data it cannot open looks for a cluster in the store's directory, no longer for the old volume.

internal/bootstrap/rootsecrets.go

@@ -47,6 +47,9 @@ const (
 	// StoreSuperuserFile is where the store's superuser password lives on the machine — the
 	// postgres module's own-secret path, so genesis and adoption write the same file.
 	StoreSuperuserFile = "/var/lib/postgres/superuser.secret"
+	// StoreDataDir is where the store keeps its data — the postgres module's data directory, so
+	// genesis raises the store where the module adopts it (novox/hq ADR 0338 §1).
+	StoreDataDir = "/var/lib/mesh-store"
 	// BusControllerFile is where the controller's password on the bus lives on the machine. Not a
 	// module's path: no module reads it — the permanent controller is handed the address the
 	// temporary one was given — and genesis keeps it only so a second run puts the same account
@@ -62,7 +65,7 @@ const (
 	// What the template says, matched exactly. A template that says something else is a template
 	// this installer does not know how to make safe, and it says so rather than guessing.
 	templateStorePassword = `"POSTGRES_PASSWORD": "bootstrap"`
-	templateStoreVolumes  = `"volumes": ["mesh-store-data:/var/lib/postgresql/data"]`
+	templateStoreVolumes  = `"volumes": ["` + StoreDataDir + `:/var/lib/postgresql/data"]`
 	templateStoreURL      = "postgres:bootstrap@"
 
 	// BusURLPlaceholder is the controller's account in its bus address, as the template names it.
@@ -265,8 +268,8 @@ func Masking(say func(string), c RootCredentials) func(string) {
 // RefuseExistingServers stops a run that would put a made credential in front of a store raised
 // by an earlier installer with the template's.
 //
-// The store's password is set by initdb, once, on an empty volume. A machine that already holds
-// `mesh-store-data` and has no credential file was raised with `bootstrap`, and minting a new
+// The store's password is set by initdb, once, on an empty data directory. A machine that already holds
+// a cluster in the store's data directory and has no credential file was raised with `bootstrap`, and minting a new
 // value here would make a bundle that dials with a password the server does not have — failing
 // three steps later, in the schemas, with nothing pointing back here. Refused by name instead,
 // with the way forward.
@@ -278,11 +281,14 @@ func RefuseExistingServers(ctx context.Context, run Runner, c RootCredentials) e
 	if !c.StoreMade {
 		return nil
 	}
-	if _, err := run(ctx, "docker", "volume", "inspect", "mesh-store-data"); err != nil {
-		return nil // no such volume: a fresh machine, which is the case this installer makes
+	// Where the store keeps its data, as the postgres module does (novox/hq ADR 0338 §2): a cluster
+	// there is one initdb already set a password for. The docker volume genesis used before is not
+	// the store's data any more, and a machine holding only that is not refused.
+	if _, err := run(ctx, "test", "-e", StoreDataDir+"/pgdata/PG_VERSION"); err != nil {
+		return nil // no cluster there: a fresh machine, which is the case this installer makes
 	}
 	return fmt.Errorf(
-		"this machine already holds the store's data (volume mesh-store-data) and no credential at %s, so it was raised "+
+		"this machine already holds the store's data (in "+StoreDataDir+") and no credential at %s, so it was raised "+
 			"by an earlier installer with the template's password. A new one made here would not open it. "+
 			"Put the password the store has into %s (0600, the value alone) and run again; then change it "+
 			"on the server and accept the new value — this installer does not rotate a running store",
@@ -311,7 +317,7 @@ func RewriteRoot(r *Rewritten, c RootCredentials) (RootRewrite, error) {
 		return out, err
 	}
 	if bundle, err = replaceOnce(bundle, templateStoreVolumes,
-		`"volumes": ["mesh-store-data:/var/lib/postgresql/data", "`+StoreSuperuserFile+":"+storeSuperuserMount+`:ro"]`,
+		`"volumes": ["`+StoreDataDir+`:/var/lib/postgresql/data", "`+StoreSuperuserFile+":"+storeSuperuserMount+`:ro"]`,
 		"the store's volumes"); err != nil {
 		return out, err
 	}