cmd/mesh-controller/release_plan.go

@@ -36,17 +36,29 @@ func tiersOf(set []string, edges []inventory.Edge) [][]string {
 	for _, m := range set {
 		deps[m] = map[string]bool{}
 	}
+	// The build seat's holders follow the controller that defines their worker (EdgeWorkerOf,
+	// novox/hq issue 206), so the built-by edge from that controller to such a holder yields: the
+	// controller is built by whichever build machine is running, as the runtime image always was.
+	worker := map[string]map[string]bool{}
+	for _, e := range edges {
+		if e.Kind == inventory.EdgeWorkerOf && in[e.From] && in[e.To] {
+			if worker[e.To] == nil {
+				worker[e.To] = map[string]bool{}
+			}
+			worker[e.To][e.From] = true
+		}
+	}
 	for _, e := range edges {
 		// A code dependency — B packages A's source — rebuilds B with A, in the same tier: B's
 		// build needs nothing of A's first. The other kinds order: stands-on and declared after
 		// the base is built, built-by after the build machine is built and running — except for
-		// what the build machine itself stands on. The runtime image is built by the builder and
-		// the builder is built on the runtime image; the image comes first, built by the builder
-		// that is running, which is the only one there could be.
+		// what the build machine itself stands on, and for the controller whose worker the build
+		// machine binds. The runtime image is built by the builder and the builder is built on the
+		// runtime image; the image comes first, built by the builder that is running.
 		if !in[e.From] || !in[e.To] || e.From == e.To || e.Kind == inventory.EdgePackages {
 			continue
 		}
-		if e.Kind == inventory.EdgeBuiltBy && isBaseOf(e.From, e.To, edges, in) {
+		if e.Kind == inventory.EdgeBuiltBy && (isBaseOf(e.From, e.To, edges, in) || worker[e.From][e.To]) {
 			continue
 		}
 		deps[e.From][e.To] = true
@@ -122,7 +134,10 @@ func reachableFrom(moved []string, edges []inventory.Edge) []string {
 	for grew := true; grew; {
 		grew = false
 		for _, e := range edges {
-			if e.Kind == inventory.EdgeBuiltBy {
+			// Built-by and worker-of order a plan; neither widens it. A new build machine changes
+			// nothing it builds, and a new controller changes nothing about the holder it orders —
+			// what packages the controller's source is already a code edge.
+			if e.Kind == inventory.EdgeBuiltBy || e.Kind == inventory.EdgeWorkerOf {
 				continue
 			}
 			if in[e.To] && !in[e.From] {

cmd/mesh-controller/worker_order_test.go

@@ -0,0 +1,45 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/novox/mesh-controller/internal/inventory"
+)
+
+// The holder of the build seat follows the controller that defines its worker (novox/hq issue 206).
+// On 2026-10-03 a plan put the build machine in tier 0 and the controller in tier 1; the new build
+// machine could not bind the worker the old controller had defined, and nothing could build the
+// controller that would have redefined it. The built-by edge from the controller to its build
+// machine yields to that order: the controller is built by whichever build machine is running.
+func TestTheBuildSeatsHolderFollowsTheControllerThatDefinesItsWorker(t *testing.T) {
+	edges := []inventory.Edge{
+		{From: "build-agent", To: "mesh-controller", Kind: inventory.EdgePackages},
+		{From: "build-agent", To: "mesh-controller", Kind: inventory.EdgeWorkerOf},
+		{From: "mesh-controller", To: "build-agent", Kind: inventory.EdgeBuiltBy},
+		{From: "route-proxy", To: "mesh-controller", Kind: inventory.EdgePackages},
+		{From: "route-proxy", To: "build-agent", Kind: inventory.EdgeBuiltBy},
+	}
+	set := reachableFrom([]string{"mesh-controller"}, edges)
+	if len(set) != 3 {
+		t.Fatalf("the controller, what packages it, and nothing more: %v", set)
+	}
+	tiers := tiersOf(set, edges)
+	pos := map[string]int{}
+	for i, tier := range tiers {
+		for _, m := range tier {
+			pos[m] = i
+		}
+	}
+	if pos["mesh-controller"] != 0 {
+		t.Fatalf("the controller first, built by the build machine that is running: %v", tiers)
+	}
+	if pos["build-agent"] <= pos["mesh-controller"] {
+		t.Fatalf("the build machine after the controller that defines its worker: %v", tiers)
+	}
+	if pos["route-proxy"] <= pos["build-agent"] {
+		t.Fatalf("what the build machine builds comes after it: %v", tiers)
+	}
+	if hasCycle(tiers, edges) {
+		t.Fatalf("no cycle here: %v", tiers)
+	}
+}

internal/inventory/dependencies.go

@@ -18,8 +18,17 @@ const (
 	EdgeBuiltBy = "built-by"
 	// EdgeDeclared: the manifest's own `build.on`.
 	EdgeDeclared = "declared"
+	// EdgeWorkerOf: the module holds the build seat, whose worker the control plane defines
+	// (novox/hq issue 206). The one place a *running* order enters the graph: a build machine rolled
+	// before the controller that redefines its worker cannot bind it, and nothing can then build the
+	// controller that would end that — so the holder of the build seat follows the controller, and
+	// the controller is built by whichever build machine is running, as it always was.
+	EdgeWorkerOf = "worker-of"
 )
 
+// TheControlPlane is the module that defines every seat's worker on the bus.
+const TheControlPlane = "mesh-controller"
+
 // Edge is one dependency: From depends on To, in the way Kind says.
 type Edge struct {
 	From string `json:"from"`
@@ -106,6 +115,13 @@ func dependenciesOf(entries []Entry, against map[string][]string, read map[strin
 			}
 		}
 	}
+	if known[TheControlPlane] {
+		for _, b := range builders {
+			if b != TheControlPlane {
+				add(b, TheControlPlane, EdgeWorkerOf)
+			}
+		}
+	}
 	sort.Slice(out, func(a, b int) bool {
 		if out[a].From != out[b].From {
 			return out[a].From < out[b].From