A have waiting for a yes says whether the move changes the build alone: the composer composes the build the module runs with today's settings and secrets and the agent compares it with what runs, so a release's Approve answers it and a changed setting is still asked (ADR 0601 §1)

cmd/mesh-host/nodeagent.go

@@ -120,7 +120,7 @@ func (h sessionHaves) Write(ctx context.Context, x agent.Have) {
 	}
 	h.session.NoteModule(ctx, link.ModuleFact{Module: x.Module, FP: x.FP, Composed: x.Composed, Phase: phase,
 		Failed: phase == string(delivery.PhaseFailed), Detail: shorten(x.Detail), Judgement: x.Judgement, Waits: x.Waits,
-		Sealed: x.Sealed})
+		BuildAlone: x.BuildAlone, Sealed: x.Sealed})
 }
 
 func (h sessionHaves) Removed(ctx context.Context, module string) {
@@ -630,7 +630,7 @@ func nodeAgent(ctx context.Context, opts options, signer ed25519.PublicKey, trus
 		composer := selfComposer(session, node, hooks, say)
 		machinesNow.Store(composer) // the machines a failing network part points at, by the placements (issue 774)
 		composerNow.Store(composer) // what the verb compose asks a pass of, this run's alone
-		env.Composed, env.SelfComposed, env.Policy = composer, true, composer.Policy
+		env.Composed, env.SelfComposed, env.Policy, env.ComposedToday = composer, true, composer.Policy, composer.ComposedToday
 		env.HoldsData = composer.HoldsData // what runs from the kept declaration says Data as its manifest does
 		session.NoteComposes(linked, delivery.ComposesOwn, "it composes its own modules, and applies no composition made elsewhere")
 		ag = agent.New(env)

internal/agent/agent.go

@@ -58,6 +58,8 @@ type Have struct {
 	// waits for a person's yes (ADR 0547 §3).
 	Judgement string
 	Waits     string
+	// BuildAlone says, in phase waiting-yes, the move changes the build alone (novox/hq ADR 0601 §1, delivery.Have.BuildAlone).
+	BuildAlone bool
 	// Sealed is, on a node composing its own, each value the composition it names carries sealed to the node's key, by
 	// slot (delivery.Have.SealedAt): kept in the have so the composer reuses them after a restart (ADR 0547 §3), each at
 	// its own slot alone (issue 1126, C1).
@@ -153,6 +155,11 @@ type Env struct {
 	// move of a module of policy record that recreates a container or moves its data waits for a person's yes in its
 	// want (ADR 0547 §3). Nil judges no move.
 	Policy func(ctx context.Context, module string) string
+	// ComposedToday is the digest of a module composed at the build fp with today's settings and secrets, as the node would
+	// compose it now, and whether it could be composed: a move to another build whose composition of the build it runs is
+	// what runs changes the build alone (novox/hq ADR 0601 §1), and the have says so. Nil: no move is said to change the
+	// build alone, and each is asked of a person.
+	ComposedToday func(ctx context.Context, module, fp string) (string, bool)
 	// HoldsData says whether a module's manifest declares data (catalogue.Manifest.DataItems), and whether its manifest
 	// could be read: what a composition's Data is, for what runs of a module from the kept declaration, which carries no
 	// Data of its own. A composition says Data, so without it a data module from the kept declaration is judged to move
@@ -1649,10 +1656,27 @@ func (a *Agent) waitsForYes(ctx context.Context, module string, w wantNow, comp
 	prev := a.running[module]
 	a.mu.Unlock()
 	a.writeHave(ctx, Have{Module: module, FP: prev.FP, Composed: prev.Composed, Phase: string(delivery.PhaseWaitingYes),
-		Detail: j.Words, Judgement: string(j.Judgement), Waits: comp.Dig})
+		Detail: j.Words, Judgement: string(j.Judgement), Waits: comp.Dig, BuildAlone: a.buildAlone(ctx, module, prev, w.Want.FP)})
 	return true
 }
 
+// buildAlone says a move of module from what runs to the build want changes the build alone (ADR 0601 §1): another build than
+// the one it runs, and the build it runs composed with today's settings and secrets is the composition it runs. Anything it
+// cannot tell is no: the move is then asked of a person.
+func (a *Agent) buildAlone(ctx context.Context, module string, prev delivery.Have, want string) bool {
+	if prev.FP == "" && prev.Composed == "" {
+		// Nothing of it run since this agent's start: its last have says what runs, as the have written keeps it.
+		if h, ok := a.env.Haves.Read(ctx, module); ok {
+			prev.FP, prev.Composed = h.FP, h.Composed
+		}
+	}
+	if a.env.ComposedToday == nil || prev.FP == "" || prev.Composed == "" || prev.FP == want {
+		return false
+	}
+	dig, ok := a.env.ComposedToday(ctx, module, prev.FP)
+	return ok && dig == prev.Composed
+}
+
 // runningComposition is what the module runs now: the composition last applied, else its resources in the declaration
 // the node kept from before the switch. Called with a.mu held.
 //

internal/agent/agent_test.go

@@ -1288,6 +1288,17 @@ func TestTheNodesOwnCompositionIsAppliedWhenItDiffersAndARecordMoveWaitsForAYes(
 		}
 		return catalogue.PolicyRoll
 	}
+	// ADR 0601 §1: what runs composed today. rec's build composed again is what it runs, so its move changes the build alone;
+	// db's is not (a setting changed too).
+	b.env.ComposedToday = func(_ context.Context, m, fp string) (string, bool) {
+		switch m {
+		case "rec":
+			return "sha256:" + strings.Repeat("8", 64), fp == fpOf("d")
+		case "db":
+			return "sha256:" + strings.Repeat("6", 64), true
+		}
+		return "", false
+	}
 	// The bucket's revisions of each key, as the verb composition reads them (issue 774).
 	var historyMu sync.Mutex
 	history := map[string][]Update{}
@@ -1452,6 +1463,9 @@ func TestTheNodesOwnCompositionIsAppliedWhenItDiffersAndARecordMoveWaitsForAYes(
 		h := b.haves.last("db")
 		return h.Phase == string(delivery.PhaseWaitingYes) && h.Waits == ddigMoved
 	})
+	if h := b.haves.last("db"); h.BuildAlone {
+		t.Errorf("a revision at the build it runs is said to change the build alone: %+v", h)
+	}
 	// The verb composition says why it waits: the revision that waits, what runs, the judgement, and with diff the
 	// container it recreates; the revision that runs, asked by its digest, is no move (issue 774).
 	keep(dk, draw)
@@ -1508,7 +1522,8 @@ func TestTheNodesOwnCompositionIsAppliedWhenItDiffersAndARecordMoveWaitsForAYes(
 	for _, row := range []struct {
 		module, fp, composed, waits string
 		sealed                      delivery.Seals
-	}{{"db", fp, "", ddig2, nil}, {"rec", recFP, recDig, rdig, delivery.Seals{"rec.key#sealed": `{"box":"rec"}`}}} {
+		alone                       bool
+	}{{"db", fp, "", ddig2, nil, false}, {"rec", recFP, recDig, rdig, delivery.Seals{"rec.key#sealed": `{"box":"rec"}`}, true}} {
 		eventually(t, row.module+"'s move did not wait for a yes", func() bool {
 			h := b.haves.last(row.module)
 			return h.Phase == string(delivery.PhaseWaitingYes) && h.Waits == row.waits
@@ -1518,6 +1533,9 @@ func TestTheNodesOwnCompositionIsAppliedWhenItDiffersAndARecordMoveWaitsForAYes(
 			(row.sealed != nil && !maps.Equal(h.Sealed, row.sealed)) {
 			t.Errorf("%s's have waiting for a yes does not keep what runs: %+v", row.module, h)
 		}
+		if h.BuildAlone != row.alone {
+			t.Errorf("%s's have waiting for a yes says build alone %v, want %v", row.module, h.BuildAlone, row.alone)
+		}
 	}
 	if got := b.appliedList(); len(got) != applied {
 		t.Fatalf("a move waiting for a yes was applied: %v", got)

internal/link/have.go

@@ -375,7 +375,7 @@ func (q *Session) writeHaves(ctx context.Context, bus Bus) {
 		h := delivery.Have{V: delivery.Version, FP: f.FP, Composed: f.Composed, Build: f.Build,
 			Phase: delivery.PhaseRunning, Health: delivery.HealthUnknown, Detail: f.Detail}
 		if delivery.Phase(f.Phase) == delivery.PhaseWaitingYes {
-			h.Judgement, h.Waits = delivery.Judgement(f.Judgement), f.Waits
+			h.Judgement, h.Waits, h.BuildAlone = delivery.Judgement(f.Judgement), f.Waits, f.BuildAlone
 		}
 		switch {
 		case f.Phase != "":

internal/link/messages.go

@@ -639,6 +639,8 @@ type ModuleFact struct {
 	// Judgement and Waits are, in phase waiting-yes, the judgement of the move and the composition waiting (ADR 0547 §3).
 	Judgement string
 	Waits     string
+	// BuildAlone says, in phase waiting-yes, the move changes the build alone (ADR 0601 §1, delivery.Have.BuildAlone).
+	BuildAlone bool
 	// Sealed is the values the composition it names carries sealed to this node's key, by slot (delivery.Have.SealedAt).
 	Sealed delivery.Seals
 }

internal/selfcompose/selfcompose.go

@@ -1635,3 +1635,48 @@ func Transient(err error) bool {
 	}
 	return false
 }
+
+// ComposedToday is the digest of module composed at the build fp with today's settings and secrets, as this node would
+// compose it now beside its other modules at their wanted builds, the boxes it runs kept as compose keeps them, and whether
+// it composed (novox/hq ADR 0601 §1): the node agent compares it with what runs, to say whether a move to another build
+// changes the build alone. A module held, a node refused, or no placement: false, and the move is asked of a person.
+func (c *Composer) ComposedToday(ctx context.Context, module, fp string) (string, bool) {
+	c.mu.Lock()
+	fps, kept := map[string]string{}, map[string]string{}
+	for m, w := range c.wants {
+		if m == agent.NodeModule {
+			continue
+		}
+		fps[m] = w.FP
+		if mm, ok := c.modules[m]; ok && mm.FP2 != w.FP {
+			kept[m] = w.FP
+		}
+	}
+	fps[module] = fp
+	delete(kept, module)
+	if mm, ok := c.modules[module]; !ok || mm.FP2 != fp {
+		kept[module] = fp
+	}
+	own, placed := c.placements[c.env.Node]
+	inOwn := c.inOwnOf(own)
+	c.mu.Unlock()
+	if !placed {
+		return "", false
+	}
+	var running []delivery.Composed
+	if c.env.Running != nil {
+		running = c.env.Running()
+	}
+	scope := frombus.Scope{Node: c.env.Node, KeptAt: kept, InOwn: inOwn, Running: running}
+	comps, _, held, err := frombus.Compose(ctx, reader{c: c}, c.env.Mesh, scope, fps)
+	if err != nil || held[module] != "" {
+		return "", false
+	}
+	for _, comp := range comps {
+		if comp.Module == module && comp.FP == fp {
+			dig, err := delivery.ComposedDigestOf(c.keepRunning(comp, running))
+			return dig, err == nil
+		}
+	}
+	return "", false
+}