The way back: a node whose placement key is deleted returns to the controller's compositions without a restart, says so in its journal and its have, and answers such a candidate as returning; pin mesh-sdk 472d5f3 (issue 1126, the seed's revert)

The seed's revert (mesh-catalog #526) was refused on 'would stop running node',
while a self-composing node would have refused its placement's absence, kept
what runs and marked every have failed until a restart. endWhenUnplaced ends the
agent's run when the key goes, so it begins again on the controller's
compositions, as at a start without a key; the composer refuses nothing while
unplaced; the node's have says whose compositions it applies (Composes); the
shadow answers a deleted placement Returns, verdict same.

cmd/mesh-host/nodeagent_integration_test.go

@@ -402,8 +402,54 @@ func TestNatsANodeThePlacementNamesComposesAndAppliesItsOwn(t *testing.T) {
 	placement, resolved, candidates := st.placement, st.resolved, st.candidates
 	hkey, place, fp := st.hkey, st.place, st.fp
 	within(t, 5*time.Second, "the node did not compose and apply its own module once placed", func() bool { return b.file("web") == "greeting=bonjour\n" })
-	_ = placement
 	h8rest(t, b, resolved, candidates, hkey, place, fp)
+	h8back(t, b, placement, candidates, hkey)
+}
+
+// h8back is the way back (issue 1126, the seed's revert): a candidate deleting the node's placement is answered as
+// returning to the controller's compositions, and the placement key deleted returns the agent to them without a
+// restart, said in the journal and the node's have, keeping what runs.
+func h8back(t *testing.T, b *itBed, placement, candidates nats.KeyValue, hkey string) {
+	t.Helper()
+	node := func() delivery.HaveNode {
+		e, err := b.haves.Get(hkey)
+		if err != nil {
+			return delivery.HaveNode{}
+		}
+		n, _ := delivery.DecodeHaveNode(e.Value())
+		return n
+	}
+	if n := node(); n.Composes != delivery.ComposesOwn {
+		t.Errorf("a node composing its own says it composes %q", n.Composes)
+	}
+	craw, err := delivery.EncodePlacementCandidate(delivery.PlacementCandidate{Group: "revert/x",
+		Pull: delivery.Head{Repository: delivery.CatalogueRepository, Number: 2, Head: "h2"}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	ckey, _ := delivery.PlacementCandidateKey("revert/x", itNode)
+	if _, err := candidates.Put(ckey, craw); err != nil {
+		t.Fatal(err)
+	}
+	within(t, 10*time.Second, "the node did not answer a candidate deleting its placement as returning", func() bool {
+		a := node().Candidates["revert/x"]
+		return a.Head == "h2" && a.Returns == delivery.ReturnsToController && a.Verdict == delivery.CandidateSame &&
+			len(a.Removed) == 0
+	})
+	ran := b.have("web").Composed
+	pkey, _ := delivery.PlacementKey(itNode)
+	if err := placement.Delete(pkey); err != nil {
+		t.Fatal(err)
+	}
+	within(t, 15*time.Second, "the node did not return to the controller's compositions when its placement went", func() bool {
+		b.mu.Lock()
+		said := strings.Join(b.said, "\n")
+		b.mu.Unlock()
+		return strings.Contains(said, "the catalogue no longer places this node") && node().Composes == delivery.ComposesController
+	})
+	if h := b.have("web"); h.Composed != ran || h.Phase == delivery.PhaseFailed || b.file("web") != "greeting=salut\n" {
+		t.Errorf("returning to the controller's compositions moved what runs: %+v, %q", h, b.file("web"))
+	}
 }
 
 // h8state is what h8 set up that the rest of H8 writes to.