The build machine takes one ask at a time, and says so while it builds

With the worker consumer's default of many deliveries in flight, every ask behind the one being
built was delivered at once, left unacknowledged for the length of the build, redelivered after the
ack wait and dropped after the fifth time: on 2026-10-01 twenty-six of forty-three builds asked in two
minutes were never built and the queue read as empty (hq issue 186). The holder's worker now has one
in flight, and a running build tells the bus it is still working, as the controller's long handlers
do, so a build longer than the ack wait is neither redelivered nor counted out.

internal/broker/derived_test.go

@@ -153,3 +153,16 @@ func TestANodesDeclarationConsumerIsWhatItsOwnGrantAllows(t *testing.T) {
 	has(t, perms.Publish, "$JS.ACK.NODES."+c.Name+".>")
 	has(t, perms.Subscribe, c.Filters[0])
 }
+
+// A holder works one ask at a time, so the server hands it one at a time (novox/hq issue 186):
+// asks queued behind the one being worked wait in the stream rather than being delivered,
+// left to expire and dropped after the fifth redelivery.
+func TestAHoldersWorkerTakesOneAskAtATime(t *testing.T) {
+	c, found := HolderConsumerFor("anchor", "builder", DeclaredSeat{Name: "mesh-build-machine", Accepts: []string{"build"}})
+	if !found {
+		t.Fatal("a seat that accepts work has no worker")
+	}
+	if c.MaxAckPending != 1 {
+		t.Fatalf("the worker may have %d asks in flight; one, so a queue is a queue", c.MaxAckPending)
+	}
+}