diff --git a/cmd/mesh-controller/dependents_test.go b/cmd/mesh-controller/dependents_test.go
new file mode 100644
index 0000000..48cf8d9
--- /dev/null
+++ b/cmd/mesh-controller/dependents_test.go
@@ -0,0 +1,52 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/novox/mesh-controller/internal/catalogue"
+	"github.com/novox/mesh-controller/internal/inventory"
+)
+
+// A merge that rebuilds a base rebuilds what stands on it, through every layer, and nothing else
+// (novox/hq issue 186): the runtime image moving means every module built on it moves too, and a
+// module built on one of those moves as well.
+func TestAMergeOfABaseTakesWhatStandsOnItAlong(t *testing.T) {
+	entry := func(name string) inventory.Entry {
+		return inventory.Entry{Manifest: catalogue.Manifest{Module: name}}
+	}
+	entries := []inventory.Entry{entry("mesh-tools"), entry("shop"), entry("shop-plugin"), entry("postgres"), entry("unrelated")}
+	against := map[string][]string{
+		"shop":        {catalogue.ArtifactStoreScheme + "mesh-tools/runtime@sha256:a"},
+		"shop-plugin": {catalogue.ArtifactStoreScheme + "shop/runtime@sha256:b"},
+		"postgres":    {catalogue.ArtifactStoreScheme + "mesh-tools/runtime@sha256:a"},
+		"unrelated":   {catalogue.ArtifactStoreScheme + "alpine/base@sha256:c"},
+	}
+	got := dependentsOf([]inventory.Entry{entry("mesh-tools")}, entries, against)
+	var names []string
+	for _, e := range got {
+		names = append(names, e.Manifest.Module)
+	}
+	want := map[string]bool{"shop": true, "shop-plugin": true, "postgres": true}
+	if len(names) != len(want) {
+		t.Fatalf("rebuilt %v; wanted exactly the three that stand on the runtime, directly or through shop", names)
+	}
+	for _, n := range names {
+		if !want[n] {
+			t.Fatalf("%s was rebuilt and stands on nothing that moved (%v)", n, names)
+		}
+	}
+	// The dependents come in base order when the merge orders them: the runtime, then shop, then
+	// the plugin that stands on shop.
+	ordered := orderByBases(append([]inventory.Entry{entry("mesh-tools")}, got...), against)
+	pos := map[string]int{}
+	for i, e := range ordered {
+		pos[e.Manifest.Module] = i
+	}
+	if !(pos["mesh-tools"] < pos["shop"] && pos["shop"] < pos["shop-plugin"]) {
+		t.Fatalf("not in base order: %v", ordered)
+	}
+	// Nothing moved: nothing follows.
+	if more := dependentsOf(nil, entries, against); len(more) != 0 {
+		t.Fatalf("with nothing moved, %d module(s) were rebuilt", len(more))
+	}
+}
diff --git a/cmd/mesh-controller/upgrades.go b/cmd/mesh-controller/upgrades.go
index b058ecf..091ce02 100644
--- a/cmd/mesh-controller/upgrades.go
+++ b/cmd/mesh-controller/upgrades.go
@@ -299,6 +299,20 @@ func (f following) SourceMoved(ctx context.Context, m link.SourceMoved) error {
 	if err != nil {
 		return notNow(err)
 	}
+	// And whatever stands on what moved. A base rebuilt without its dependents is a mesh half on
+	// the old image until somebody remembers to ask — on 2026-10-01 forty-two modules, twice, by
+	// hand (novox/hq issue 186). The relation is the one `build --on` reads; this is the same
+	// rebuild, asked by the merge that made it necessary, in base order.
+	standing := dependentsOf(moved, entries, against)
+	if len(standing) > 0 {
+		var on []string
+		for _, e := range standing {
+			on = append(on, e.Manifest.Module)
+		}
+		fmt.Printf("  %d module(s) stand on what moved and are rebuilt with it: %s\n",
+			len(standing), strings.Join(on, ", "))
+		moved = append(moved, standing...)
+	}
 	ordered := orderByBases(moved, against)
 	names := make([]string, 0, len(ordered))
 	for _, e := range ordered {
@@ -522,3 +536,37 @@ func isHistory(mergedAt string, seen time.Time) bool {
 	}
 	return at.Before(seen)
 }
+
+// dependentsOf is every catalogued module that stands on one of the moved modules, directly or
+// through another dependent, and is not itself among them — in the catalogue's order, so the
+// answer is the same each time. A module standing on nothing that moved is left alone: a merge
+// rebuilds what it changed and what is built on top of that, not the catalogue.
+func dependentsOf(moved, entries []inventory.Entry, against map[string][]string) []inventory.Entry {
+	bases := map[string]bool{}
+	for _, e := range moved {
+		bases[e.Manifest.Module] = true
+	}
+	var out []inventory.Entry
+	taken := map[string]bool{}
+	for grew := true; grew; {
+		grew = false
+		for _, e := range entries {
+			name := e.Manifest.Module
+			if bases[name] || taken[name] {
+				continue
+			}
+			for base := range bases {
+				if standsOnModule(e, base, against) {
+					taken[name] = true
+					out = append(out, e)
+					grew = true
+					break
+				}
+			}
+		}
+		for _, e := range out {
+			bases[e.Manifest.Module] = true
+		}
+	}
+	return out
+}