Keep a named push from sending builds a policy or a plan holds back

A named push flushed every other machine whose declaration differed from
what it was last sent (hq ADR 0083). Under an upgrade policy of `record`,
or a plan still waiting on its first machine (ADR 0218), every machine
running the module differs, so `push <one>` sent the held build to all of
them (hq issue 259).

Each send now records which build of each module it carried
(node.sent_builds, migration 0061). The cascade, and the bus holder added
to a named push, skip a machine any of whose modules would move to a
build its policy records or an open plan has not sent it, and say which
module, which build, why, and that `push <node>` sends it. A machine
whose last send was not recorded is held until it is named. The named
machine itself, a whole-mesh push and `push --behind` are unchanged.

cmd/mesh-controller/adopting_test.go

@@ -85,7 +85,7 @@ func reportsReaching(t *testing.T, open *stores, reachable []link.Reach, held ..
 	if err != nil {
 		t.Fatal(err)
 	}
-	if err := open.inventory.RecordSent(ctx, record.ID, digestOf(body)); err != nil {
+	if err := open.inventory.RecordSent(ctx, record.ID, digestOf(body), nil); err != nil {
 		t.Fatal(err)
 	}
 	if _, err := (link.Enrolment{Inventory: open.inventory}).Heard(ctx, link.Report{

cmd/mesh-controller/held_back.go

@@ -0,0 +1,241 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"sort"
+	"strings"
+
+	"github.com/novox/mesh-controller/internal/catalogue"
+	"github.com/novox/mesh-controller/internal/inventory"
+)
+
+// A push sends no build a policy or a plan holds back, except to the machine it names (novox/hq
+// issue 259, ADR 0221).
+//
+// A named push ends by sending every other machine whose declaration differs from what it was last
+// sent (ADR 0083), so that a grant the push's work minted reaches the provider in the same act. A
+// digest cannot say why a machine differs. A module whose upgrade policy records rather than rolls
+// out makes every machine running it differ from the merge on, and so did a module whose plan was
+// still waiting on its first machine (ADR 0218): `push <anchor>` sent all four machines the build
+// that was meant to be walked through the mesh one machine at a time, and a fault in it was met
+// everywhere at once.
+//
+// What tells the two apart is which build of each module the machine was last sent, kept with every
+// send. A machine any of whose modules would move to a build its policy or an open plan holds back
+// is not sent by a push that did not name it; the push says which, and why, and how to send it.
+
+// heldBack is why a push that did not name a machine must not send it, empty when it may.
+//
+// `modules` is what the machine would be sent now; `sent` and `known` what it was last sent, as
+// Inventory.SentBuilds answers. A module moves when the build it would carry is not the one the
+// machine was last sent — including a module the machine was never sent at all. A move is held when
+// the module's policy records rather than rolls out, or when an open plan has not yet sent this
+// machine (planStillToSend). A machine whose last send was not recorded is held whole: what it carried
+// is not known, so a held upgrade cannot be told from anything else.
+func heldBack(node string, modules []string, sent map[string]string, known bool,
+	current map[string]inventory.CurrentBuild, plans []inventory.Plan) []string {
+	if !known {
+		return []string{"which builds it was last sent is not known — it was last sent before the " +
+			"mesh kept them, or sent a declaration by hand"}
+	}
+	var why []string
+	for _, m := range modules {
+		now := current[m]
+		was, carried := sent[m]
+		if carried && was == now.Commit {
+			continue
+		}
+		move := fmt.Sprintf("%s would move %sto %s", m, fromBuild(was, carried), buildName(now.Commit))
+		if !now.RollOut {
+			why = append(why, move+", which its upgrade policy records rather than rolls out")
+			continue
+		}
+		if id := planStillToSend(plans, m, node); id != "" {
+			why = append(why, move+", which "+id+" has not sent it yet (one machine first)")
+		}
+	}
+	sort.Strings(why)
+	return why
+}
+
+// planStillToSend is the open plan that has a module's new build still to send this machine, or empty:
+// one holding the module that has neither finished sending it nor sent it here first, and has not
+// failed it (novox/hq ADR 0218). The same reading rolledOutByAPlan makes for the whole module, made
+// per machine.
+func planStillToSend(plans []inventory.Plan, module, node string) string {
+	for _, p := range plans {
+		s, holds := p.Modules[module]
+		if !p.Open() || !holds {
+			continue
+		}
+		if s == nil {
+			return p.ID
+		}
+		if s.SentAt != nil || s.State == "failed" {
+			continue
+		}
+		first := false
+		for _, n := range s.First {
+			if n == node {
+				first = true
+			}
+		}
+		if !first {
+			return p.ID
+		}
+	}
+	return ""
+}
+
+func fromBuild(was string, carried bool) string {
+	if !carried {
+		return "(never sent it) "
+	}
+	return "from " + buildName(was) + " "
+}
+
+func buildName(commit string) string {
+	if commit == "" {
+		return "a build with no source"
+	}
+	return shortCommit(commit)
+}
+
+// heldMachines reads, for each machine named, why a push that did not name it must not send it
+// (heldBack), and answers only the machines held. A machine whose set cannot be worked out is left
+// to the send, which says why.
+func heldMachines(ctx context.Context, open *stores, names []string) (map[string][]string, error) {
+	out := map[string][]string{}
+	if len(names) == 0 {
+		return out, nil
+	}
+	inv := open.inventory
+	current, err := inv.CurrentBuilds(ctx)
+	if err != nil {
+		return nil, err
+	}
+	plans, err := inv.OpenPlans(ctx)
+	if err != nil {
+		return nil, err
+	}
+	for _, node := range names {
+		plan, _, err := planFor(ctx, open, node)
+		if err != nil {
+			continue
+		}
+		modules := make([]string, 0, len(plan.Modules))
+		for _, m := range plan.Modules {
+			modules = append(modules, m.Module)
+		}
+		sent, known, err := inv.SentBuilds(ctx, node)
+		if err != nil {
+			return nil, err
+		}
+		if why := heldBack(node, modules, sent, known, current, plans); len(why) > 0 {
+			out[node] = why
+		}
+	}
+	return out, nil
+}
+
+// sayHeld is what a push says about a machine it left behind on purpose: that it is behind, why it
+// was not sent, that whatever else it is owed waits with it, and the command that sends it.
+func sayHeld(w io.Writer, node string, why []string) {
+	fmt.Fprintf(w, "\n%s is behind and was not sent: %s. A push sends no build a policy or a plan "+
+		"holds back to a machine it did not name (novox/hq ADR 0221), so anything else it is owed — a "+
+		"grant from this push among it — waits with it. `push %s` sends it\n",
+		node, strings.Join(why, "; "), node)
+}
+
+// flushBehind is the end of a named push: every other machine now behind is sent too, by name, over
+// as many rounds as the sends take to settle (novox/hq issue 057, ADR 0083) — except a machine whose
+// modules would move to a build a policy or a plan holds back, which is named and left (ADR 0221).
+//
+// `handled` is every machine already sent or already said; it is not considered again. Answers the
+// machines that could not be composed, as refusals.
+func flushBehind(ctx context.Context, open *stores, nodes []inventory.Node, handled map[string]bool,
+	compose func(held context.Context, node string) (sendable, error), d delivery, holder string,
+	w io.Writer) ([]string, error) {
+	inv := open.inventory
+	var refusals []string
+	// Bounded by the node count: a node is marked handled the round it is considered and is never
+	// considered twice, so the loop cannot run more than len(nodes) rounds. The bound is a guard
+	// against a logic error, not a real limit — if it were ever hit, that is a bug rather than a
+	// cascade legitimately still converging, so it is said rather than passed over in silence.
+	rounds := 0
+	for {
+		would, err := wouldSend(ctx, open, nodes)
+		if err != nil {
+			return refusals, err
+		}
+		behind, err := inv.Waiting(ctx, would)
+		if err != nil {
+			return refusals, err
+		}
+		var also []string
+		for _, m := range behind {
+			if !handled[m.Node] {
+				also = append(also, m.Node)
+			}
+		}
+		if len(also) == 0 {
+			return refusals, nil
+		}
+		if rounds++; rounds > len(nodes) {
+			fmt.Fprintf(w, "\nstopped cascading after %d rounds with %s still behind — this "+
+				"should not happen; run `push --behind` to finish\n",
+				rounds-1, strings.Join(also, ", "))
+			return refusals, nil
+		}
+		sort.Strings(also)
+		held, err := heldMachines(ctx, open, also)
+		if err != nil {
+			return refusals, err
+		}
+		var sending []string
+		for _, name := range also {
+			// Every candidate this round is marked handled — the sent ones so they are not
+			// re-listed, the held ones because they stay held, and the refused ones so a machine
+			// that cannot be composed does not make the loop spin on it for ever.
+			handled[name] = true
+			if why, isHeld := held[name]; isHeld {
+				sayHeld(w, name, why)
+				continue
+			}
+			sending = append(sending, name)
+		}
+		if len(sending) == 0 {
+			continue
+		}
+		fmt.Fprintf(w, "\nthis push left %s behind — a provision granted from there, or a "+
+			"declaration since changed; sending it too\n", strings.Join(sending, ", "))
+		// Tolerantly, exactly as the named send: a machine that cannot be composed is collected as
+		// a refusal and reported at the end, and the others are still sent (novox/hq ADR 0066).
+		// Held for this round only, and after the last round's were given back, so two pushes
+		// cascading into each other's machines never each wait on the other.
+		refused, err := sendRound(ctx, open, sending, compose, d, holder)
+		refusals = append(refusals, refused...)
+		if err != nil {
+			return refusals, err
+		}
+	}
+}
+
+// composeForPush is how a push composes one machine: its set resolved, what it cannot host and what
+// is left out of it said, and its declaration allocated.
+func composeForPush(open *stores, gens map[string]catalogue.Generator) func(held context.Context, node string) (sendable, error) {
+	return func(held context.Context, node string) (sendable, error) {
+		plan, settings, err := planFor(held, open, node)
+		if err != nil {
+			return sendable{}, err
+		}
+		reportUnhostable(node, plan)
+		declared, err := declarationWith(held, open, node, plan, settings, gens, Allocating)
+		if err == nil {
+			reportLeftOut(node, declared)
+		}
+		return declared, err
+	}
+}

cmd/mesh-controller/held_back_test.go

@@ -0,0 +1,335 @@
+package main
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"reflect"
+	"slices"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/novox/mesh-controller/internal/catalogue"
+	"github.com/novox/mesh-controller/internal/inventory"
+	"github.com/novox/mesh-controller/internal/overlay"
+)
+
+// novox/hq issue 259, ADR 0221: a push that did not name a machine does not send it a build its
+// upgrade policy records rather than rolls out, nor one an open plan has not sent it yet. Anything
+// else that moved is still a consequence the push sends (ADR 0083).
+func TestAHeldBuildHoldsAMachineANamedPushDidNotName(t *testing.T) {
+	current := map[string]inventory.CurrentBuild{
+		"resolver": {Commit: "c2c2c2c2c2"},
+		"agent":    {Commit: "a2", RollOut: true},
+		"network":  {},
+	}
+	modules := []string{"network", "resolver", "agent"}
+	sent := map[string]string{"network": "", "resolver": "c1c1c1c1c1", "agent": "a2"}
+
+	// A module whose policy records moved: held, naming it, both builds and why.
+	why := heldBack("laptop", modules, sent, true, current, nil)
+	if len(why) != 1 || !strings.Contains(why[0], "resolver would move from c1c1c1c1 to c2c2c2c2") ||
+		!strings.Contains(why[0], "upgrade policy records") {
+		t.Fatalf("a recorded upgrade did not hold the machine: %v", why)
+	}
+
+	// Nothing moved — what differs is a grant, a peer, a setting: not held (issue 057).
+	sent["resolver"] = "c2c2c2c2c2"
+	if why := heldBack("laptop", modules, sent, true, current, nil); len(why) != 0 {
+		t.Fatalf("a machine whose builds are all current was held: %v", why)
+	}
+
+	// A module whose policy rolls out moved, and no plan holds it: sent, as before.
+	sent["agent"] = "a1"
+	if why := heldBack("laptop", modules, sent, true, current, nil); len(why) != 0 {
+		t.Fatalf("a rolled-out upgrade no plan holds was held: %v", why)
+	}
+
+	// The last send's builds are not known: held whole.
+	if why := heldBack("laptop", modules, nil, false, current, nil); len(why) != 1 ||
+		!strings.Contains(why[0], "not known") {
+		t.Fatalf("a machine whose last send was not recorded was not held: %v", why)
+	}
+
+	// A module the machine was never sent, under a recording policy: held, and said so.
+	delete(sent, "resolver")
+	sent["agent"] = "a2"
+	if why := heldBack("laptop", modules, sent, true, current, nil); len(why) != 1 ||
+		!strings.Contains(why[0], "resolver would move (never sent it) to c2c2c2c2") {
+		t.Fatalf("a module never sent under a recording policy: %v", why)
+	}
+}
+
+// ADR 0218 meets ADR 0083: a plan waiting on its first machine has not sent the rest, and a push
+// naming some other machine must not send them for it.
+func TestAPlanWaitingOnItsFirstMachineHoldsTheRest(t *testing.T) {
+	at := time.Now()
+	current := map[string]inventory.CurrentBuild{"agent": {Commit: "a2", RollOut: true}}
+	sent := map[string]string{"agent": "a1"}
+	waiting := []inventory.Plan{{ID: "plan-7", State: inventory.PlanRolling, Modules: map[string]*inventory.PlanModule{
+		"agent": {State: "built", First: []string{"ace"}, FirstAt: &at}}}}
+
+	why := heldBack("g14", []string{"agent"}, sent, true, current, waiting)
+	if len(why) != 1 || !strings.Contains(why[0], "plan-7 has not sent it yet") {
+		t.Fatalf("a machine the plan has not reached was not held: %v", why)
+	}
+	// The first machine itself was sent by the plan: not held by it.
+	if why := heldBack("ace", []string{"agent"}, sent, true, current, waiting); len(why) != 0 {
+		t.Fatalf("the plan's first machine was held: %v", why)
+	}
+	// Built but not yet sent anywhere, or not yet built: the plan has it still to send.
+	for what, s := range map[string]*inventory.PlanModule{"built, unsent": {State: "built"}, "unasked": nil} {
+		plans := []inventory.Plan{{ID: "plan-8", State: inventory.PlanBuilding,
+			Modules: map[string]*inventory.PlanModule{"agent": s}}}
+		if why := heldBack("ace", []string{"agent"}, sent, true, current, plans); len(why) != 1 {
+			t.Errorf("%s: not held: %v", what, why)
+		}
+	}
+	// Sent everywhere, failed, or a plan no longer open: the plan holds nothing back.
+	for what, plans := range map[string][]inventory.Plan{
+		"sent everywhere": {{ID: "p", State: inventory.PlanRolling, Modules: map[string]*inventory.PlanModule{
+			"agent": {State: "built", First: []string{"ace"}, FirstAt: &at, SentAt: &at}}}},
+		"failed": {{ID: "p", State: inventory.PlanRolling, Modules: map[string]*inventory.PlanModule{
+			"agent": {State: "failed"}}}},
+		"closed": {{ID: "p", State: inventory.PlanDone, Modules: map[string]*inventory.PlanModule{
+			"agent": {State: "built"}}}},
+	} {
+		if why := heldBack("g14", []string{"agent"}, sent, true, current, plans); len(why) != 0 {
+			t.Errorf("%s: held: %v", what, why)
+		}
+	}
+}
+
+// A send records the build of each module it carried; a module left out of it keeps the build it
+// was last sent, since the machine keeps that one.
+func TestASendCarriesTheCurrentBuildsAndALeftOutModuleKeepsItsOwn(t *testing.T) {
+	current := map[string]inventory.CurrentBuild{"a": {Commit: "a2"}, "b": {Commit: "b2"}, "c": {}}
+	got := carriedBuilds([]string{"a", "b", "c"}, map[string]string{"b": "a setting does not compose"},
+		current, map[string]string{"a": "a1", "b": "b1"})
+	if want := map[string]string{"a": "a2", "b": "b1", "c": ""}; !reflect.DeepEqual(got, want) {
+		t.Fatalf("carried %v, wanted %v", got, want)
+	}
+	// Not known before: the left-out module is not recorded at all, so it reads as never sent.
+	got = carriedBuilds([]string{"a", "b"}, map[string]string{"b": "x"}, current, nil)
+	if want := map[string]string{"a": "a2"}; !reflect.DeepEqual(got, want) {
+		t.Fatalf("carried %v, wanted %v", got, want)
+	}
+}
+
+// recordedDelivery sends nothing and records each send as the mesh does, so the next comparison
+// reads the machine as current — and writes down which machines it declared.
+type recordedDelivery struct {
+	inv      *inventory.Inventory
+	declared []string
+}
+
+func (r *recordedDelivery) grant(context.Context, []readyNode) error { return nil }
+
+func (r *recordedDelivery) declare(ctx context.Context, s readyNode, body []byte) (string, error) {
+	r.declared = append(r.declared, s.node)
+	return recordSent(ctx, r.inv, s.node, body, s.declared.Builds)
+}
+
+// aResolver is a module built from a repository, at a commit, with something on the machine that
+// says which build it is.
+func aResolver(t *testing.T, open *stores, commit string, asked time.Time) {
+	t.Helper()
+	m := catalogue.Manifest{Module: "resolver", Version: "1", Resources: []map[string]any{
+		{"id": "zones", "type": "file", "path": "/etc/resolver/zones", "content": "built from " + commit},
+	}}
+	if err := open.inventory.RegisterModule(t.Context(), m, inventory.Source{
+		Repository: "novox/mesh-catalog", Path: "modules/resolver", BuiltFrom: commit, Asked: asked}); err != nil {
+		t.Fatal(err)
+	}
+}
+
+// A third machine on the private network: once it is sent, every other machine's peers change with
+// it, which is a consequence a push must still send — no build moved.
+func aThirdMachine(t *testing.T, open *stores) {
+	t.Helper()
+	ctx := t.Context()
+	record, err := open.inventory.AddNode(ctx, "spare")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := open.inventory.SetPlace(ctx, "spare", "spare.example:51820", "here", false, "10.77.0.3"); err != nil {
+		t.Fatal(err)
+	}
+	reported, err := json.Marshal(map[string]any{"capabilities": []map[string]any{
+		{"name": "container-runtime", "present": true}, {"name": "wireguard", "present": true},
+		{"name": "systemd", "present": true}}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	var profile map[string]any
+	if err := json.Unmarshal(reported, &profile); err != nil {
+		t.Fatal(err)
+	}
+	if err := open.inventory.RecordProfile(ctx, record.ID, profile); err != nil {
+		t.Fatal(err)
+	}
+	if err := open.inventory.RecordSealingKey(ctx, record.ID, aPublicKey(t)); err != nil {
+		t.Fatal(err)
+	}
+	if err := open.inventory.RecordOverlayKey(ctx, record.ID, aPublicKey(t)); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := open.inventory.Assign(ctx, "spare", overlay.Name); err != nil {
+		t.Fatal(err)
+	}
+}
+
+// The issue as it happened, against the real stores: a change merged with the policy `record`, a push
+// naming the anchor, and the laptop — running the same module — left with what it had, by name.
+func TestANamedPushLeavesAMachineAPolicyHoldsBack(t *testing.T) {
+	open := aMesh(t)
+	ctx := t.Context()
+	inv := open.inventory
+	asked := time.Now().Add(-time.Hour)
+	aResolver(t, open, "c1c1c1c1c1", asked)
+	for _, node := range []string{"anchor", "laptop"} {
+		if _, err := inv.Assign(ctx, node, "resolver"); err != nil {
+			t.Fatal(err)
+		}
+	}
+	gens, err := generators(ctx, open)
+	if err != nil {
+		t.Fatal(err)
+	}
+	compose := composeForPush(open, gens)
+	d := &recordedDelivery{inv: inv}
+	if _, err := sendRound(ctx, open, []string{"anchor", "laptop"}, compose, d, ""); err != nil {
+		t.Fatal(err)
+	}
+	if builds, known, err := inv.SentBuilds(ctx, "laptop"); err != nil || !known || builds["resolver"] != "c1c1c1c1c1" {
+		t.Fatalf("the send did not record the build it carried: %v %v %v", builds, known, err)
+	}
+	digestOfLaptop := func() string {
+		sent, err := inv.Outstanding(ctx, "laptop")
+		if err != nil {
+			t.Fatal(err)
+		}
+		return sent
+	}
+	before := digestOfLaptop()
+
+	// The change merges; the policy is the default, record. `push anchor` sends the anchor...
+	aResolver(t, open, "c2c2c2c2c2", asked.Add(time.Minute))
+	d.declared = nil
+	if _, err := sendRound(ctx, open, []string{"anchor"}, compose, d, ""); err != nil {
+		t.Fatal(err)
+	}
+	// ...and its cascade leaves the laptop, saying so.
+	var said bytes.Buffer
+	d.declared = nil
+	refused, err := flushBehind(ctx, open, mustNodes(t, open), map[string]bool{"anchor": true}, compose, d, "", &said)
+	if err != nil || len(refused) != 0 {
+		t.Fatalf("the cascade failed: %v %v", refused, err)
+	}
+	if len(d.declared) != 0 {
+		t.Fatalf("the cascade sent %v a build its policy records", d.declared)
+	}
+	if digestOfLaptop() != before {
+		t.Fatal("the laptop's last send moved: it was sent the held build")
+	}
+	for _, want := range []string{"laptop is behind and was not sent", "resolver would move from c1c1c1c1 to c2c2c2c2",
+		"upgrade policy records", "`push laptop` sends it"} {
+		if !strings.Contains(said.String(), want) {
+			t.Errorf("the push did not say %q:\n%s", want, said.String())
+		}
+	}
+
+	// Held and owed something else at once — a peer joined: still not sent, and both said: why it
+	// is held, and that what else it is owed waits with it.
+	aThirdMachine(t, open)
+	d.declared = nil
+	if _, err := sendRound(ctx, open, []string{"spare"}, compose, d, ""); err != nil {
+		t.Fatal(err)
+	}
+	d.declared = nil
+	said.Reset()
+	if _, err := flushBehind(ctx, open, mustNodes(t, open), map[string]bool{"anchor": true, "spare": true},
+		compose, d, "", &said); err != nil {
+		t.Fatal(err)
+	}
+	if len(d.declared) != 0 || digestOfLaptop() != before {
+		t.Fatalf("a held machine owed a consequence was sent: %v", d.declared)
+	}
+	if !strings.Contains(said.String(), "resolver would move") || !strings.Contains(said.String(), "anything else it is owed") {
+		t.Fatalf("the push did not say both:\n%s", said.String())
+	}
+
+	// A policy that rolls out: the laptop is a consequence like any other, and sent.
+	if err := inv.SetUpgradeOf(ctx, "resolver", inventory.Upgrade{RollOut: true}); err != nil {
+		t.Fatal(err)
+	}
+	said.Reset()
+	if _, err := flushBehind(ctx, open, mustNodes(t, open), map[string]bool{"anchor": true, "spare": true},
+		compose, d, "", &said); err != nil {
+		t.Fatal(err)
+	}
+	if !reflect.DeepEqual(d.declared, []string{"laptop"}) || digestOfLaptop() == before {
+		t.Fatalf("a rolled-out upgrade's machine was not sent: %v\n%s", d.declared, said.String())
+	}
+	if builds, _, _ := inv.SentBuilds(ctx, "laptop"); builds["resolver"] != "c2c2c2c2c2" {
+		t.Fatalf("the new send did not record the new build: %v", builds)
+	}
+}
+
+// Issue 057's case is unchanged: a machine whose builds are all current and whose declaration moved
+// for another reason is sent by a push that names someone else.
+func TestANamedPushStillSendsAConsequenceNothingHolds(t *testing.T) {
+	open := aMesh(t)
+	ctx := t.Context()
+	inv := open.inventory
+	aResolver(t, open, "c1c1c1c1c1", time.Now().Add(-time.Hour))
+	if _, err := inv.Assign(ctx, "laptop", "resolver"); err != nil {
+		t.Fatal(err)
+	}
+	gens, err := generators(ctx, open)
+	if err != nil {
+		t.Fatal(err)
+	}
+	compose := composeForPush(open, gens)
+	d := &recordedDelivery{inv: inv}
+	if _, err := sendRound(ctx, open, []string{"anchor", "laptop"}, compose, d, ""); err != nil {
+		t.Fatal(err)
+	}
+
+	// `push spare`, the machine just placed: the others' peers change with it.
+	aThirdMachine(t, open)
+	if _, err := sendRound(ctx, open, []string{"spare"}, compose, d, ""); err != nil {
+		t.Fatal(err)
+	}
+	d.declared = nil
+	var said bytes.Buffer
+	if _, err := flushBehind(ctx, open, mustNodes(t, open), map[string]bool{"spare": true}, compose, d, "", &said); err != nil {
+		t.Fatal(err)
+	}
+	if !reflect.DeepEqual(d.declared, []string{"anchor", "laptop"}) {
+		t.Fatalf("a consequence nothing holds was not sent: %v\n%s", d.declared, said.String())
+	}
+	if strings.Contains(said.String(), "was not sent") {
+		t.Fatalf("a machine nothing holds was said to be held:\n%s", said.String())
+	}
+
+	// A machine whose last send was not recorded — a declaration sent by hand — is held until named.
+	record, err := inv.NodeByName(ctx, "laptop")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := inv.RecordSent(ctx, record.ID, "sent-by-hand", nil); err != nil {
+		t.Fatal(err)
+	}
+	d.declared = nil
+	said.Reset()
+	if _, err := flushBehind(ctx, open, mustNodes(t, open), map[string]bool{"spare": true}, compose, d, "", &said); err != nil {
+		t.Fatal(err)
+	}
+	// The anchor, the hub, may still be settling from the machine placed above; the laptop is the
+	// question.
+	if slices.Contains(d.declared, "laptop") || !strings.Contains(said.String(), "laptop is behind and was not sent") {
+		t.Fatalf("a machine whose last send is not known was sent: %v\n%s", d.declared, said.String())
+	}
+}

cmd/mesh-controller/issue_204_test.go

@@ -77,7 +77,7 @@ func TestASendIsRecordedEvenWhenTheSenderIsBeingCancelled(t *testing.T) {
 	}
 	cancel() // the sender is going away: its context is cancelled between the send and the record
 	body := []byte(`{"declaration":1,"resources":[]}`)
-	digest, err := recordSent(ctx, inv, "anchor", body)
+	digest, err := recordSent(ctx, inv, "anchor", body, nil)
 	if err != nil {
 		// NodeByName on the cancelled context may itself refuse; the record must still be possible
 		// through the detached context, so look the node up again on a live one.

cmd/mesh-controller/plan.go

@@ -397,9 +397,49 @@ func declarationWith(ctx context.Context, open *stores, node string,
 	if err != nil {
 		return sendable{}, err
 	}
-	return sendable{Resources: composed.Resources, Adoption: adoption,
+	out := sendable{Resources: composed.Resources, Adoption: adoption,
 		Received: composed.Received, Mesh: with.Mesh, BusUsers: with.BusUsers,
-		LeftOut: sortedKeysOf(composed.LeftOut), leftOutWhy: composed.LeftOut}, nil
+		LeftOut: sortedKeysOf(composed.LeftOut), leftOutWhy: composed.LeftOut}
+	// And which build of each module it carries, for the send to record (novox/hq issue 259, ADR
+	// 0221). Read only on the send path: a question about what would be sent records nothing.
+	if choosing == Allocating {
+		current, err := open.inventory.CurrentBuilds(ctx)
+		if err != nil {
+			return sendable{}, err
+		}
+		before, known, err := open.inventory.SentBuilds(ctx, node)
+		if err != nil {
+			return sendable{}, err
+		}
+		if !known {
+			before = nil
+		}
+		names := make([]string, 0, len(plan.Modules))
+		for _, m := range plan.Modules {
+			names = append(names, m.Module)
+		}
+		out.Builds = carriedBuilds(names, composed.LeftOut, current, before)
+	}
+	return out, nil
+}
+
+// carriedBuilds is the build of each module a declaration carries, as a send records it (novox/hq
+// issue 259): the module's current build for each module in it, and for a module left out of it
+// (ADR 0163, rule 6) the build it was last sent, since the machine keeps that one — or nothing, when
+// that is not known. Never nil, so a send through here always records what it knows.
+func carriedBuilds(modules []string, leftOut map[string]string, current map[string]inventory.CurrentBuild,
+	before map[string]string) map[string]string {
+	out := map[string]string{}
+	for _, m := range modules {
+		if _, left := leftOut[m]; left {
+			if was, kept := before[m]; kept {
+				out[m] = was
+			}
+			continue
+		}
+		out[m] = current[m].Commit
+	}
+	return out
 }
 
 // sortedKeysOf is a map's keys, sorted — so what a declaration says it left out does not move

cmd/mesh-controller/push.go

@@ -217,8 +217,9 @@ func declare(ctx context.Context, args []string) error {
 	}
 	// Written down like every other send (novox/hq issue 204): a declaration a person sent by hand
 	// is still what the machine was last told, and status must not read it as current for the one
-	// the mesh would compose.
-	if _, err := recordSent(ctx, inv, node, raw); err != nil {
+	// the mesh would compose. Which builds it carried is recorded as not known (novox/hq issue 259):
+	// the mesh did not compose it, so a push that does not name this machine treats it as held.
+	if _, err := recordSent(ctx, inv, node, raw, nil); err != nil {
 		return err
 	}
 	fmt.Printf("sent %s a signed declaration (%d bytes)\n", node, len(raw))
@@ -367,6 +368,23 @@ func pushCommand(ctx context.Context, args []string) error {
 	if err != nil {
 		return err
 	}
+	// **Not when its own modules are held back** (novox/hq issue 259, ADR 0221): added rather than
+	// named, it is sent its whole declaration, and a build its policy records or a plan has not sent
+	// it yet would go with the user list. Named and left, with what that costs.
+	saidHeld := map[string]bool{}
+	if holderBehind && len(args) == 1 {
+		held, err := heldMachines(ctx, open, []string{holder})
+		if err != nil {
+			return err
+		}
+		if why, isHeld := held[holder]; isHeld {
+			sayHeld(os.Stdout, holder, why)
+			fmt.Printf("%s holds the bus, and the user list it would carry has changed: until it is "+
+				"sent, the bus may refuse what this push's machines were newly granted\n", holder)
+			holderBehind = false
+			saidHeld[holder] = true
+		}
+	}
 	asked = brokerFirst(asked, holder, holderBehind)
 
 	// Held from composing to sending, so a converge on one of them cannot send between the two
@@ -418,76 +436,21 @@ func pushCommand(ctx context.Context, args []string) error {
 	//
 	// Compared against what each machine was last SENT, not against a before/after of this push:
 	// the mint usually happened at `assign` or `module issue`, before this command ran, so the
-	// only durable signal is "what it should be" versus "what it last received". A machine behind
-	// for an unrelated reason is caught here too, which is not a cost — a named push that knew a
-	// machine was behind and left it so would be the very silence this removes. Bounded: a
+	// only durable signal is "what it should be" versus "what it last received". Bounded: a
 	// flushed send may itself mint, so this converges over a few rounds.
+	//
+	// **Except a machine a policy or a plan holds back** (novox/hq issue 259, ADR 0221): one whose
+	// modules would move to a build their upgrade policy records rather than rolls out, or that an
+	// open plan has not sent it yet. It is named, with why, and left for a push that names it.
 	if len(args) == 1 {
-		flushed := map[string]bool{args[0]: true}
-		// Bounded by the node count: a node is marked flushed the round it is handled and is
-		// never handled twice, so the loop cannot run more than len(nodes) rounds. The bound is
-		// a guard against a logic error, not a real limit — if it were ever hit, that is a bug
-		// rather than a cascade legitimately still converging, so it is said rather than passed
-		// over in silence, unlike the earlier fixed cap that could stop a real cascade short.
-		rounds := 0
-		for {
-			would, err := wouldSend(ctx, open, nodes)
-			if err != nil {
-				return err
-			}
-			behind, err := inv.Waiting(ctx, would)
-			if err != nil {
-				return err
-			}
-			var also []string
-			for _, m := range behind {
-				if !flushed[m.Node] {
-					also = append(also, m.Node)
-				}
-			}
-			if len(also) == 0 {
-				break
-			}
-			if rounds++; rounds > len(nodes) {
-				fmt.Printf("\nstopped cascading after %d rounds with %s still behind — this "+
-					"should not happen; run `push --behind` to finish\n",
-					rounds-1, strings.Join(also, ", "))
-				break
-			}
-			sort.Strings(also)
-			fmt.Printf("\nthis push left %s behind — a provision granted from there, or a "+
-				"declaration since changed; sending it too\n", strings.Join(also, ", "))
-			// Tolerantly, exactly as the named send above: a machine that cannot be composed is
-			// collected as a refusal and reported at the end, and the others are still sent
-			// (novox/hq ADR 0066). The earlier cut routed these through sendTo, which is
-			// all-or-nothing — so one swept machine's compose error failed the operator's named
-			// push and skipped its --wait, the very intolerance the main path exists to avoid.
-			// Held for this round only, and after the last round's were given back, so two pushes
-			// cascading into each other's machines never each wait on the other.
-			refused, err := sendRound(ctx, open, also,
-				func(held context.Context, node string) (sendable, error) {
-					plan, settings, err := planFor(held, open, node)
-					if err != nil {
-						return sendable{}, err
-					}
-					reportUnhostable(node, plan)
-					declared, err := declarationWith(held, open, node, plan, settings, gens, Allocating)
-					if err == nil {
-						reportLeftOut(node, declared)
-					}
-					return declared, err
-				},
-				bus, holder)
-			refusals = append(refusals, refused...)
-			if err != nil {
-				return err
-			}
-			// Every candidate this round is marked handled — the sent ones so they are not
-			// re-listed, and the refused ones so a machine that cannot be composed does not make
-			// the loop spin on it for ever. Its refusal is already in the report.
-			for _, name := range also {
-				flushed[name] = true
-			}
+		handled := map[string]bool{args[0]: true}
+		for n := range saidHeld {
+			handled[n] = true
+		}
+		refused, err := flushBehind(ctx, open, nodes, handled, composeForPush(open, gens), bus, holder, os.Stdout)
+		refusals = append(refusals, refused...)
+		if err != nil {
+			return err
 		}
 	}
 
@@ -762,7 +725,7 @@ func (b overTheBus) declare(ctx context.Context, s readyNode, body []byte) (stri
 	}
 	// After it is away, not before. A digest recorded for something that failed to send would make
 	// the machine look current for a declaration it never received.
-	digest, err := recordSent(ctx, b.open.inventory, s.node, body)
+	digest, err := recordSent(ctx, b.open.inventory, s.node, body, s.declared.Builds)
 	if err != nil {
 		return "", err
 	}
@@ -1244,7 +1207,11 @@ func allot(ctx context.Context, inv *inventory.Inventory, node string) (int64, e
 // never wrote it down: status read "applied, current" over a machine that had just been sent
 // something else. What was sent was sent; the record of it must not depend on the sender living
 // another second. Bounded, so a store that is away does not hold a dying process open for ever.
-func recordSent(ctx context.Context, inv *inventory.Inventory, node string, body []byte) (string, error) {
+//
+// And the build of each module it carried (novox/hq issue 259, ADR 0221), nil when that is not known:
+// what tells a machine held back by a policy or a plan from one a push left behind.
+func recordSent(ctx context.Context, inv *inventory.Inventory, node string, body []byte,
+	builds map[string]string) (string, error) {
 	kept, cancel := context.WithTimeout(context.WithoutCancel(ctx), 10*time.Second)
 	defer cancel()
 	record, err := inv.NodeByName(kept, node)
@@ -1252,7 +1219,7 @@ func recordSent(ctx context.Context, inv *inventory.Inventory, node string, body
 		return "", err
 	}
 	digest := digestOf(body)
-	if err := inv.RecordSent(kept, record.ID, digest); err != nil {
+	if err := inv.RecordSent(kept, record.ID, digest, builds); err != nil {
 		return "", err
 	}
 	return digest, nil

cmd/mesh-controller/sendable.go

@@ -43,6 +43,10 @@ type sendable struct {
 	LeftOut []string
 	// leftOutWhy is why each was, for push and plan to say; never on the wire.
 	leftOutWhy map[string]string
+	// Builds is the build of each module this declaration carries — module to the commit its build
+	// was made from — recorded with the send and never on the wire (novox/hq issue 259, ADR 0221).
+	// Composed only on the send path; nil records that it is not known.
+	Builds map[string]string
 }
 
 // adoptionEnvelope is what an adopted node is told about its mode. Taken is every module taken on

internal/inventory/catalogue.go

@@ -1158,6 +1158,37 @@ func (i *Inventory) SetUpgradeOf(ctx context.Context, module string, u Upgrade)
 	return nil
 }
 
+// CurrentBuild is the build a module is at and whether its policy rolls a new one out (novox/hq
+// issue 259).
+type CurrentBuild struct {
+	// Commit is the commit the module's manifest was read at — its `built_from` — and empty for a
+	// module held without a source.
+	Commit string
+	// RollOut is the module's upgrade policy, as Upgrade.RollOut.
+	RollOut bool
+}
+
+// CurrentBuilds is every module's current build and upgrade policy, in one read: what a send records
+// it carried, and what a push compares a machine's last send against.
+func (i *Inventory) CurrentBuilds(ctx context.Context) (map[string]CurrentBuild, error) {
+	rows, err := i.store.Pool().Query(ctx,
+		`select name, coalesce(built_from, ''), upgrade = 'roll-out' from module`)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	out := map[string]CurrentBuild{}
+	for rows.Next() {
+		var name string
+		var b CurrentBuild
+		if err := rows.Scan(&name, &b.Commit, &b.RollOut); err != nil {
+			return nil, err
+		}
+		out[name] = b
+	}
+	return out, rows.Err()
+}
+
 // Running is every machine assigned a module, in a stable order.
 //
 // **Assigned, not reported.** A machine that is assigned the module and has not applied it yet is

internal/inventory/doing_test.go

@@ -189,7 +189,7 @@ func TestAMachineIsWaitingWhenWhatItWasSentIsNotWhatItShouldBe(t *testing.T) {
 	}
 
 	// Sent what it should be: not waiting.
-	if err := inv.RecordSent(ctx, anchor.ID, "aaa"); err != nil {
+	if err := inv.RecordSent(ctx, anchor.ID, "aaa", nil); err != nil {
 		t.Fatal(err)
 	}
 	waiting, err = inv.Waiting(ctx, map[string]string{"anchor": "aaa", "laptop": "bbb"})
@@ -234,7 +234,7 @@ func TestAMachineWithNothingComputedForItIsNotWaiting(t *testing.T) {
 	// It has been sent something before, which is what makes this the case the guard is for: a
 	// machine with a digest and nothing computed for it would compare against the empty string
 	// and look out of date, when the truth is that nobody worked out what it should be.
-	if err := inv.RecordSent(ctx, node.ID, "what-it-got-last-time"); err != nil {
+	if err := inv.RecordSent(ctx, node.ID, "what-it-got-last-time", nil); err != nil {
 		t.Fatal(err)
 	}
 	waiting, err := inv.Waiting(ctx, map[string]string{})

internal/inventory/migrations/0061-a-send-records-the-builds-it-carried.sql

@@ -0,0 +1,14 @@
+-- A send records the build of each module it carried (novox/hq issue 259, ADR 0221).
+--
+-- A named push ends by sending every other machine whose declaration differs from what it was last
+-- sent (ADR 0083). Read from the declaration's digest alone, a module whose upgrade policy records
+-- rather than rolls out, or whose plan sends one machine first (ADR 0218), made every machine running
+-- it differ, so `push <one machine>` sent all of them the build the policy was holding back. Which
+-- build of each module a machine was last sent is what tells a held upgrade from a consequence of the
+-- push, and it is not in a digest.
+--
+-- Module name to the commit its build was made from — the module's `built_from` when the declaration
+-- was composed, empty for a module the mesh holds without a source. NULL for a machine last sent
+-- before this was kept, or sent a declaration by hand: what it carried is not known, and the push
+-- treats such a machine as held until it is pushed by name.
+alter table node add column sent_builds jsonb;

internal/inventory/nodes.go

@@ -909,18 +909,53 @@ func (i *Inventory) LastReports(ctx context.Context) ([]Reported, error) {
 	return out, rows.Err()
 }
 
-// RecordSent keeps a digest of the declaration a machine was last sent.
+// RecordSent keeps a digest of the declaration a machine was last sent, and the build of each module
+// it carried.
 //
 // **A digest rather than the declaration.** The mesh can compute what a machine should be at any
 // moment; keeping a copy would be a second account of it, able to disagree with the first. What
 // cannot be recomputed is what was *actually sent*, and that is the whole difference between a
 // machine that is out of date and one that has never been told.
-func (i *Inventory) RecordSent(ctx context.Context, node, digest string) error {
+//
+// **And which build of each module** (novox/hq issue 259, ADR 0221): module name to the commit its
+// build was made from. A digest cannot say whether a machine differs because a module moved to a build
+// its upgrade policy holds back, or because of something a push made — a grant — and only the second
+// is a push's to send to a machine it did not name. Nil records that it is not known, as for a
+// declaration sent by hand.
+func (i *Inventory) RecordSent(ctx context.Context, node, digest string, builds map[string]string) error {
+	var carried *string
+	if builds != nil {
+		raw, err := json.Marshal(builds)
+		if err != nil {
+			return err
+		}
+		text := string(raw)
+		carried = &text
+	}
 	_, err := i.store.Pool().Exec(ctx,
-		`update node set sent = $2, sent_at = now() where id = $1`, node, digest)
+		`update node set sent = $2, sent_at = now(), sent_builds = $3::jsonb where id = $1`, node, digest, carried)
 	return err
 }
 
+// SentBuilds is the build of each module a machine was last sent, by its name: module to the commit
+// its build was made from (novox/hq issue 259). Known is false when that was not kept — a machine
+// last sent before it was, sent a declaration by hand, or one the mesh does not know.
+func (i *Inventory) SentBuilds(ctx context.Context, name string) (builds map[string]string, known bool, err error) {
+	var raw []byte
+	err = i.store.Pool().QueryRow(ctx, `select sent_builds from node where name = $1`, name).Scan(&raw)
+	if errors.Is(err, pgx.ErrNoRows) {
+		return nil, false, nil
+	}
+	if err != nil || raw == nil {
+		return nil, false, err
+	}
+	builds = map[string]string{}
+	if err := json.Unmarshal(raw, &builds); err != nil {
+		return nil, false, err
+	}
+	return builds, true, nil
+}
+
 // RecordSentBusUsers keeps a digest of the bus's user list a machine was just sent, by its name
 // (novox/hq issue 249): whether the machine holding the bus must go first is whether this differs
 // from the list composed now.

internal/inventory/sent_builds_test.go

@@ -0,0 +1,81 @@
+package inventory
+
+import (
+	"reflect"
+	"testing"
+
+	"github.com/novox/mesh-controller/internal/catalogue"
+)
+
+// novox/hq issue 259: a send keeps which build of each module it carried. A machine never sent
+// anything, or sent with nothing recorded — before this was kept, or by hand — is not known, which
+// is not the same as having been sent nothing.
+func TestASendKeepsTheBuildsItCarried(t *testing.T) {
+	inv := ForTest(t)
+	ctx := t.Context()
+	node, err := inv.AddNode(ctx, "anchor")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if builds, known, err := inv.SentBuilds(ctx, "anchor"); err != nil || known || builds != nil {
+		t.Fatalf("a machine never sent anything has known builds %v (%v): %v", builds, known, err)
+	}
+
+	carried := map[string]string{"resolver": "abc123", "network": ""}
+	if err := inv.RecordSent(ctx, node.ID, "d1", carried); err != nil {
+		t.Fatal(err)
+	}
+	builds, known, err := inv.SentBuilds(ctx, "anchor")
+	if err != nil || !known || !reflect.DeepEqual(builds, carried) {
+		t.Fatalf("the builds sent were not kept: %v %v %v", builds, known, err)
+	}
+
+	// Sent with nothing carried: known, and empty.
+	if err := inv.RecordSent(ctx, node.ID, "d2", map[string]string{}); err != nil {
+		t.Fatal(err)
+	}
+	if builds, known, err := inv.SentBuilds(ctx, "anchor"); err != nil || !known || len(builds) != 0 {
+		t.Fatalf("an empty send: %v %v %v", builds, known, err)
+	}
+
+	// Sent by hand: not known, and the digest still recorded.
+	if err := inv.RecordSent(ctx, node.ID, "d3", nil); err != nil {
+		t.Fatal(err)
+	}
+	if builds, known, err := inv.SentBuilds(ctx, "anchor"); err != nil || known || builds != nil {
+		t.Fatalf("a send whose builds are not known read as %v %v: %v", builds, known, err)
+	}
+	if sent, err := inv.Outstanding(ctx, "anchor"); err != nil || sent != "d3" {
+		t.Fatalf("the digest was not recorded with it: %q %v", sent, err)
+	}
+
+	if _, known, err := inv.SentBuilds(ctx, "nobody"); err != nil || known {
+		t.Fatalf("a machine the mesh does not know: %v %v", known, err)
+	}
+}
+
+// A module's current build is the commit its manifest was read at, with its upgrade policy.
+func TestTheCurrentBuildsAreTheCatalogues(t *testing.T) {
+	inv := ForTest(t)
+	ctx := t.Context()
+	if err := inv.RegisterModule(ctx, catalogue.Manifest{Module: "resolver", Version: "1"},
+		Source{Repository: "novox/mesh-catalog", BuiltFrom: "c1"}); err != nil {
+		t.Fatal(err)
+	}
+	if err := inv.RegisterModule(ctx, catalogue.Manifest{Module: "by-hand", Version: "1"}, Source{}); err != nil {
+		t.Fatal(err)
+	}
+	if err := inv.SetUpgradeOf(ctx, "by-hand", Upgrade{RollOut: true}); err != nil {
+		t.Fatal(err)
+	}
+	current, err := inv.CurrentBuilds(ctx)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := current["resolver"]; got != (CurrentBuild{Commit: "c1"}) {
+		t.Errorf("resolver is at %+v", got)
+	}
+	if got := current["by-hand"]; got != (CurrentBuild{RollOut: true}) {
+		t.Errorf("a module with no source is at %+v", got)
+	}
+}

internal/link/heard_test.go

@@ -100,7 +100,7 @@ func TestABareAliveDoesNotWipeTheDeclarationThatSaysANodeIsCurrent(t *testing.T)
 	}
 	// The mesh sent this node a declaration, and the node applied it and named which by digest.
 	const digest = "d640d1b6a1b2c3d4e5f60718293a4b5c6d7e8f90a1b2c3d4e5f6071829304152"
-	if err := inv.RecordSent(ctx, node.ID, digest); err != nil {
+	if err := inv.RecordSent(ctx, node.ID, digest, nil); err != nil {
 		t.Fatal(err)
 	}
 	if _, err := (link.Enrolment{Inventory: inv}).Heard(ctx, link.Report{