Name the build slice without a dash so it sits beside user.slice, and restart it when its limits change (issue 1798)

internal/builder/kill_test.go

@@ -150,9 +150,9 @@ func TestAVolumeAlreadyGoneIsNoFailure(t *testing.T) {
 func TestEveryContainerJoinsTheNodesBuildSlice(t *testing.T) {
 	was := CgroupParent
 	defer func() { CgroupParent = was }()
-	CgroupParent = "mesh-build.slice"
+	CgroupParent = "meshbuild.slice"
 	got := LabelledArgs("docker", []string{"run", "--rm", "img", "sh"}, "build-1")
-	want := []string{"run", "--label", "mesh.build=build-1", "--cgroup-parent", "mesh-build.slice", "--rm", "img", "sh"}
+	want := []string{"run", "--label", "mesh.build=build-1", "--cgroup-parent", "meshbuild.slice", "--rm", "img", "sh"}
 	if !reflect.DeepEqual(got, want) {
 		t.Errorf("1798/AC1: docker run became %v", got)
 	}

modules/build-agent/files/build-agent.env

@@ -6,4 +6,4 @@ MESH_NPM_TOKEN_FILE=/run/mesh/package-registry.secret
 MESH_GENESIS_PACKAGE_REGISTRY=/run/mesh/genesis-package-registry.json
 MESH_WORKSPACE=${dir:workspace}
 MESH_JUDGE_CACHE=${dir:judge-cache}
-MESH_BUILD_CGROUP_PARENT=mesh-build.slice
+MESH_BUILD_CGROUP_PARENT=meshbuild.slice

modules/build-agent/files/meshbuild.slice

@@ -1,7 +1,7 @@
 # Managed by the mesh (module build-agent). Replaced on every push; edit the module's settings instead.
 #
 # Everything a build or check starts on this machine runs in this slice (novox/hq issue 1798): the build
-# agent starts every container with --cgroup-parent=mesh-build.slice. The weights only bind while the machine
+# agent starts every container with --cgroup-parent=meshbuild.slice. The weights only bind while the machine
 # is busy, so an idle machine still builds at full speed; the memory limits are the part that always binds.
 [Slice]
 CPUWeight=${setting:cpu-weight}

modules/build-agent/manifest_test.go

@@ -203,7 +203,7 @@ func TestTheBuildSliceCarriesTheMachinesLimits(t *testing.T) {
 	if err := json.Unmarshal(raw, &m); err != nil {
 		t.Fatal(err)
 	}
-	slice, err := os.ReadFile("files/mesh-build.slice")
+	slice, err := os.ReadFile("files/meshbuild.slice")
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -217,17 +217,31 @@ func TestTheBuildSliceCarriesTheMachinesLimits(t *testing.T) {
 	}
 	var placed, running bool
 	for _, r := range read(t).Resources {
-		placed = placed || (r["type"] == "file" && r["path"] == "/etc/systemd/system/mesh-build.slice")
+		placed = placed || (r["type"] == "file" && r["path"] == "/etc/systemd/system/meshbuild.slice")
-		running = running || (r["type"] == "service" && r["unit"] == "mesh-build.slice" && r["state"] == "running")
+		running = running || (r["type"] == "service" && r["unit"] == "meshbuild.slice" && r["state"] == "running")
 	}
 	if !placed || !running {
 		t.Errorf("1798/AC2: the slice must be placed (%v) and running (%v)", placed, running)
 	}
+	// 1798/AC3: a dash in a slice's name nests it in the slice named before the dash, and cgroup v2 weights only
+	// compare siblings, so the name has none and the slice sits at the top level beside user.slice.
+	for _, r := range read(t).Resources {
+		if r["type"] == "service" && r["unit"] == "meshbuild.slice" {
+			if strings.Contains(strings.TrimSuffix(r["unit"].(string), ".slice"), "-") {
+				t.Errorf("1798/AC3: slice name %v nests", r["unit"])
+			}
+			// 1798/AC4: a changed limit reaches systemd only if the unit restarts when its file changes.
+			restart, _ := r["restart-on"].([]any)
+			if len(restart) != 1 || restart[0] != "build-slice" {
+				t.Errorf("1798/AC4: the slice unit does not restart on its file: %v", restart)
+			}
+		}
+	}
 	env, err := os.ReadFile("files/build-agent.env")
 	if err != nil {
 		t.Fatal(err)
 	}
-	if !strings.Contains(string(env), "MESH_BUILD_CGROUP_PARENT=mesh-build.slice") {
+	if !strings.Contains(string(env), "MESH_BUILD_CGROUP_PARENT=meshbuild.slice") {
 		t.Error("1798/AC1: the agent is not told the slice's name")
 	}
 }

modules/build-agent/module.json

@@ -105,16 +105,19 @@
     {
       "id": "build-slice",
       "type": "file",
-      "path": "/etc/systemd/system/mesh-build.slice",
+      "path": "/etc/systemd/system/meshbuild.slice",
       "mode": "0644",
       "trusted": false,
-      "template": "files/mesh-build.slice"
+      "template": "files/meshbuild.slice"
     },
     {
       "id": "build-slice-unit",
       "type": "service",
-      "unit": "mesh-build.slice",
+      "unit": "meshbuild.slice",
-      "state": "running"
+      "state": "running",
+      "restart-on": [
+        "build-slice"
+      ]
     },
     {
       "id": "agent-env",