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.

internal/selfcompose/selfcompose.go

@@ -429,9 +429,16 @@ func (c *Composer) compose(ctx context.Context) []agent.Update {
 	_, nodeWanted := c.wants[agent.NodeModule]
 	// What it runs inside its own composition and no want names at a build of the new form stays there, as the
 	// controller's composed writer folds it (issue 1126); compose folds none a want names.
-	inOwn := c.inOwnOf(c.placements[c.env.Node])
+	own, placed := c.placements[c.env.Node]
+	inOwn := c.inOwnOf(own)
 	r := reader{c: c}
 	c.mu.Unlock()
+	if !placed {
+		// The catalogue no longer places it: the agent returns to the controller's compositions (endWhenUnplaced), and
+		// this is no refusal of what it runs (issue 1126, the seed's revert).
+		c.sayOnce("the catalogue no longer places this node: it composes nothing of its own, and keeps running what it runs")
+		return nil
+	}
 	// Composed from the build its want names (frombus.Scope.KeptAt, issue 1126).
 	for _, module := range behind {
 		kept[module] = fps[module]

internal/selfcompose/selfcompose_test.go

@@ -477,6 +477,15 @@ func TestTheNodeComposesItsWantsFromTheBus(t *testing.T) {
 	candidate("adds", 4, "lemurs", "keeper")
 	candidate("drops", 5)
 	candidate("ghost", 6, "lemurs", "ghost")
+	// A head deleting n1's placement file (the seed's revert, mesh-catalog #526): n1 returns to the controller's
+	// compositions, answered as such, not as every module removed.
+	if raw, err := delivery.EncodePlacementCandidate(delivery.PlacementCandidate{Group: "deletes",
+		Pull: delivery.Head{Repository: delivery.CatalogueRepository, Number: 1, Head: "h-deletes"}}); err != nil {
+		t.Fatal(err)
+	} else {
+		k, _ := delivery.PlacementCandidateKey("deletes", "n1")
+		sb.put(delivery.PlacementCandidatesBucket, k, raw, 7)
+	}
 	sb.caught()
 	var answers map[string]delivery.CandidateAnswer
 	waitFor := func(why string, ok func(map[string]delivery.CandidateAnswer) bool) {
@@ -490,7 +499,7 @@ func TestTheNodeComposesItsWantsFromTheBus(t *testing.T) {
 			}
 		}
 	}
-	waitFor("every group answered", func(a map[string]delivery.CandidateAnswer) bool { return len(a) == 4 })
+	waitFor("every group answered", func(a map[string]delivery.CandidateAnswer) bool { return len(a) == 5 })
 	// Every watch and get the shadow makes is one the node's grant allows (issue 1126, 2026-10-27 09:21).
 	sb.mu.Lock()
 	for _, w := range sb.watches {
@@ -520,6 +529,10 @@ func TestTheNodeComposesItsWantsFromTheBus(t *testing.T) {
 		"ghost": func(a delivery.CandidateAnswer) bool {
 			return a.Verdict == delivery.CandidateRefused && a.Refused != ""
 		},
+		"deletes": func(a delivery.CandidateAnswer) bool {
+			return a.Verdict == delivery.CandidateSame && a.Returns == delivery.ReturnsToController && a.Revision == 7 &&
+				len(a.Removed) == 0
+		},
 	} {
 		if !want(answers[group]) {
 			t.Errorf("%s: %+v", group, answers[group])
@@ -534,7 +547,7 @@ func TestTheNodeComposesItsWantsFromTheBus(t *testing.T) {
 	}
 	k, _ := delivery.PlacementCandidateKey("same", "n1")
 	sb.del(delivery.PlacementCandidatesBucket, k)
-	waitFor("the deleted group's answer stays", func(a map[string]delivery.CandidateAnswer) bool { _, ok := a["same"]; return !ok && len(a) == 3 })
+	waitFor("the deleted group's answer stays", func(a map[string]delivery.CandidateAnswer) bool { _, ok := a["same"]; return !ok && len(a) == 4 })
 
 	// Review of L2b, round 2: a watch ends while the link stays; a group's key is deleted before the shadow watches
 	// again. The new run reads afresh, so that group is no longer answered.
@@ -546,7 +559,7 @@ func TestTheNodeComposesItsWantsFromTheBus(t *testing.T) {
 	sb.missing(delivery.PlacementCandidatesBucket, false)
 	waitFor("a group deleted while the shadow was down is still answered", func(a map[string]delivery.CandidateAnswer) bool {
 		_, ok := a["drops"]
-		return !ok && len(a) == 2
+		return !ok && len(a) == 3
 	})
 
 	// Issue 1126, the seed's review: a module n1 runs inside its own composition (nats, at a build of the old form) is

internal/selfcompose/shadow.go

@@ -292,18 +292,11 @@ func (s *Shadow) answerGroup(ctx context.Context, group string) (delivery.Candid
 		running = c.env.Running()
 	}
 	if p, ok := given[node]; ok && p == nil {
-		// The head removes this node's placement file: everything it runs is removed.
-		a := delivery.CandidateAnswer{Head: head, Revision: rev}
-		for _, r := range running {
-			if r.Module == "" {
-				a.Removed = append(a.Removed, delivery.HaveNodeWord)
-			} else {
-				a.Removed = append(a.Removed, r.Module)
-			}
-		}
-		sort.Strings(a.Removed)
-		a.Verdict = delivery.VerdictOf(a)
-		return a, true
+		// The head deletes this node's placement file: the node then returns to the controller's compositions, as one the
+		// catalogue does not place (endWhenUnplaced), and keeps what runs; nothing is removed (issue 1126, the seed's
+		// revert, whose check read "would stop running node").
+		return delivery.CandidateAnswer{Head: head, Revision: rev, Returns: delivery.ReturnsToController,
+			Verdict: delivery.CandidateSame}, true
 	}
 
 	placement := given[node]