Two faults found on review

A second Accept value would have overwritten the first, because the header was Set per value rather
than Added. One value is all any caller passes today, so nothing was wrong — but a helper that
quietly keeps only the last of what it was given is a trap for whoever passes two.

And a replayed announcement that could not be written was published as an empty body: a fact on the
mesh that says nothing, which the reader can only log and drop. It is now said and skipped, because a
body that cannot be marshalled is this program's fault rather than the bus's.

internal/builder/registry.go

@@ -137,7 +137,7 @@ func (r Registry) has(ctx context.Context, url string, accept ...string) (bool,
 		return false, err
 	}
 	for _, media := range accept {
-		request.Header.Set("Accept", media)
+		request.Header.Add("Accept", media)
 	}
 	response, err := r.client().Do(request)
 	if err != nil {

internal/catalogue/declaration.go

@@ -1685,7 +1685,10 @@ func prepared(from map[string]any) map[string]any {
 	for k, v := range from {
 		step[k] = v
 	}
-	step["id"] = fmt.Sprint(from["id"]) + ".prepare"
+	// **A hyphen, not a dot.** A resource's id is `<module>.<its own id>`, and a module's name may
+	// itself contain a dot (`novox.be`), so the module is everything before the *last* dot — which
+	// only works if what the mesh derives adds no dot of its own.
+	step["id"] = fmt.Sprint(from["id"]) + "-prepare"
 	step["name"] = fmt.Sprint(from["name"]) + "-prepare"
 	step["run-once"] = true
 	step["args"] = []any{PreparationArgument}

internal/catalogue/prepares_test.go

@@ -3,6 +3,7 @@ package catalogue
 import (
 	"encoding/json"
 	"fmt"
+	"strings"
 	"testing"
 )
 
@@ -57,13 +58,18 @@ func TestThePreparationRunsTheModulesOwnCodeAndComesRightBeforeIt(t *testing.T)
 	ids := idsOf(out)
 	at := -1
 	for i, id := range ids {
-		if id == "gitea.runtime.prepare" {
+		if id == "gitea.runtime-prepare" {
 			at = i
 		}
 	}
 	if at < 0 {
 		t.Fatalf("nothing prepares this module's state: %v", ids)
 	}
+	// A module's name may contain a dot, so a resource's module is everything before the last one —
+	// which the derived id must not add to, or a machine reads the wrong owner from it.
+	if strings.Count("gitea.runtime-prepare", ".") != 1 {
+		t.Fatal("the derived id adds a dot, so what owns it cannot be read from it")
+	}
 	if ids[at+1] != "gitea.runtime" {
 		t.Fatalf("the preparation is not immediately before the module's own code: %v", ids)
 	}
@@ -79,7 +85,7 @@ func TestThePreparationRunsTheModulesOwnCodeAndComesRightBeforeIt(t *testing.T)
 func TestThePreparationIsGivenWhatTheModuleIsGiven(t *testing.T) {
 	out := declaredFor(t, aPreparingModule())
 	declared := byID(out)
-	step, workload := declared["gitea.runtime.prepare"], declared["gitea.runtime"]
+	step, workload := declared["gitea.runtime-prepare"], declared["gitea.runtime"]
 	if step == nil || workload == nil {
 		t.Fatalf("expected both, got %v", idsOf(out))
 	}
@@ -108,7 +114,7 @@ func TestAModuleThatPreparesNothingGetsNoStep(t *testing.T) {
 	m := aPreparingModule()
 	m.Prepares = false
 	for _, id := range idsOf(declaredFor(t, m)) {
-		if id == "gitea.runtime.prepare" {
+		if id == "gitea.runtime-prepare" {
 			t.Fatal("a module that prepares nothing was given a preparation")
 		}
 	}

internal/link/serve.go

@@ -476,7 +476,15 @@ func (s *Server) catchingUp(ctx context.Context, m Control) {
 		// module's event from a module called "control-plane", which does not exist — so the
 		// controller's own account refused it, every catalogue that asked what it missed was
 		// answered with nothing, and its graph kept the gap (found 2026-09-28).
-		if err := s.bus.PublishSeatEvent(ctx, MeshControllerSeat, KeyBuiltBefore, replayed(a)); err != nil {
+		body, err := json.Marshal(a)
+		if err != nil {
+			// A body that cannot be written is this program's fault, not the bus's, and publishing
+			// an empty one would put a fact on the mesh that says nothing.
+			s.log.Printf("cannot re-announce %s at %s: %v", a.Module, short(a.Commit), err)
+			_ = m.Took()
+			return
+		}
+		if err := s.bus.PublishSeatEvent(ctx, MeshControllerSeat, KeyBuiltBefore, body); err != nil {
 			// Said and abandoned rather than retried: the catalogue asks again every time it
 			// starts, and half a graph delivered twice is no better than half delivered once.
 			s.log.Printf("replaying %s at %s failed, and the rest is abandoned: %v",
@@ -601,15 +609,3 @@ func (s *Server) saysWhatItDid(ctx context.Context, report Report) {
 		s.log.Printf("could not say that %s %s: %v", report.Node, event, err)
 	}
 }
-
-// replayed is one announcement as the control plane states it. The same body the build machine's
-// outcome carries, because what the catalogue does with it is the same.
-func replayed(a Announcement) []byte {
-	raw, err := json.Marshal(a)
-	if err != nil {
-		// A body that cannot be marshalled is a programming error, not a bus failure, and an empty
-		// one is refused by the reader rather than silently taken as an announcement of nothing.
-		return nil
-	}
-	return raw
-}