A container may add supplementary groups, and a group may be a config value filled at composition (issue 1636, ADR 0480 clause 7)

go/declaration/declaration.go

@@ -1454,6 +1454,14 @@ type Container struct {
 	// container runs as its image says. Its key is `identity`, the manifest's word; the field is not, because
 	// a resource's Identity is its id.
 	RunAs *ContainerIdentity `json:"identity,omitempty"`
+
+	// Groups are the supplementary groups the container's process joins, as numbers, each passed to the runtime
+	// as a group to add (novox/hq ADR 0480 clause 7, issue 1636): n8n writes the media library through the
+	// library's group, which a stock image knows nothing of. Each is above zero and below the kernel's "no group"
+	// (ADR 0328 §15: never root). Part of the spec, so a change recreates the container. Absent: none are added.
+	// An older node-engine refuses the key (strict decoding), so the controller sends it only to a node that
+	// reports it reads it.
+	Groups []int64 `json:"groups,omitempty"`
 }
 
 // The ways an image is told who to run as (novox/hq ADR 0325 §2).
@@ -1521,6 +1529,30 @@ func (i *ContainerIdentity) problems(where string, env map[string]string) []stri
 	return problems
 }
 
+// groupProblems refuses a supplementary group that is root's or below it, the kernel's "no group" number, or a
+// number named twice (novox/hq ADR 0480 clause 7, ADR 0328 §15).
+func (c *Container) groupProblems(where string) []string {
+	var problems []string
+	seen := map[int64]bool{}
+	for _, g := range c.Groups {
+		switch {
+		case g == 0:
+			problems = append(problems, fmt.Sprintf("%s: container %s adds group 0, and the mesh never makes or keeps anything "+
+				"as root: a supplementary group is never root's (novox/hq ADR 0328 §15)", where, c.Name))
+		case g < 0:
+			problems = append(problems, fmt.Sprintf("%s: container %s adds group %d, below zero: a group is a whole number "+
+				"above zero", where, c.Name, g))
+		case g >= 1<<32-1:
+			problems = append(problems, fmt.Sprintf("%s: container %s adds group %d, which is the kernel's \"no group\" "+
+				"number or beyond it", where, c.Name, g))
+		case seen[g]:
+			problems = append(problems, fmt.Sprintf("%s: container %s adds group %d twice", where, c.Name, g))
+		}
+		seen[g] = true
+	}
+	return problems
+}
+
 func (c *Container) Identity() string { return c.ID }
 func (c *Container) Kind() Type       { return TypeContainer }
 func (c *Container) Target() string   { return c.Name }
@@ -1603,6 +1635,7 @@ func (c *Container) validate(where string, _ bool) []string {
 			"runs and exits, and joins nothing afterwards")
 	}
 	problems = append(problems, c.RunAs.problems(where+": container "+c.Name, c.Env)...)
+	problems = append(problems, c.groupProblems(where)...)
 	return append(problems, checkImage(where, c.Image)...)
 }