Merge branch 'feat/compose-once' of /home/jochen/projects/novox/mesh-sdk-compose into feat/node-packages

go/compose/frombus/frombus.go

@@ -223,9 +223,56 @@ func taken(name string, raw []byte, m delivery.Module) (man catalogue.Manifest,
 // manifest is refused is read for its offer alone (unusable). A manifest the bus does not answer for still ends the
 // read: that is the bus's, not the module's.
 func input(ctx context.Context, r Reader, mesh Mesh, s Scope, refuse func(module string, err error), wanted map[string]string) (compose.Input, error) {
+	b, err := readBase(ctx, r, mesh, s)
+	b.refuseOwn(refuse)
+	if err != nil {
+		return compose.Input{}, err
+	}
+	return b.finish(ctx, r, r.Build, mesh, s, b.in, refuse, wanted)
+}
+
+// base is the part of a node's input that the fingerprints it composes its modules at leave alone (issue 1954): read once
+// for its plans at the wanted builds and at the newest, whose builds alone differ (PlansHeldTwice).
+type base struct {
+	in         compose.Input
+	placements map[string]delivery.Placement
+	records    map[string]delivery.NodeRecord
+	modules    map[string]delivery.Module
+	// ownRefused is each module placed on the composing node whose manifest the indexer refused, with why, in the order
+	// read: every scope holds it.
+	ownRefused [][2]string
+}
+
+// refuseOwn hands refuse each module placed on the composing node whose manifest is refused.
+func (b base) refuseOwn(refuse func(module string, err error)) {
+	if refuse == nil {
+		return
+	}
+	for _, r := range b.ownRefused {
+		refuse(r[0], errors.New(r[1]))
+	}
+}
+
+// cloned is the input with its own catalogue, nodes and kept manifests, what finishing it sets: two scopes finished over
+// one base never see each other's builds.
+func (b base) cloned() compose.Input {
+	in := b.in
+	in.Catalogue = maps.Clone(b.in.Catalogue)
+	in.Nodes = slices.Clone(b.in.Nodes)
+	for i := range in.Nodes {
+		in.Nodes[i].Kept = maps.Clone(in.Nodes[i].Kept)
+	}
+	in.KeptCoreBoxes = slices.Clone(b.in.KeptCoreBoxes)
+	in.OwnSecrets = slices.Clone(b.in.OwnSecrets)
+	return in
+}
+
+// readBase is input up to the builds: placement, records, the indexer's modules and manifests, each node's values.
+func readBase(ctx context.Context, r Reader, mesh Mesh, s Scope) (base, error) {
+	var b base
 	placements, err := r.Placements(ctx)
 	if err != nil {
-		return compose.Input{}, fmt.Errorf("frombus: placement: %w", err)
+		return b, fmt.Errorf("frombus: placement: %w", err)
 	}
 	if len(s.Placements) > 0 {
 		given := make(map[string]delivery.Placement, len(placements)+len(s.Placements))
@@ -238,7 +285,7 @@ func input(ctx context.Context, r Reader, mesh Mesh, s Scope, refuse func(module
 				continue
 			}
 			if p.Node != node {
-				return compose.Input{}, fmt.Errorf("frombus: the placement given for %s names the node %q", node, p.Node)
+				return b, fmt.Errorf("frombus: the placement given for %s names the node %q", node, p.Node)
 			}
 			given[node] = *p
 		}
@@ -246,14 +293,14 @@ func input(ctx context.Context, r Reader, mesh Mesh, s Scope, refuse func(module
 	}
 	records, err := r.Records(ctx)
 	if err != nil {
-		return compose.Input{}, fmt.Errorf("frombus: node records: %w", err)
+		return b, fmt.Errorf("frombus: node records: %w", err)
 	}
 	modules, err := r.Modules(ctx)
 	if err != nil {
-		return compose.Input{}, fmt.Errorf("frombus: the indexer's modules: %w", err)
+		return b, fmt.Errorf("frombus: the indexer's modules: %w", err)
 	}
 	if _, ok := placements[s.Node]; !ok && !s.Every {
-		return compose.Input{}, fmt.Errorf("frombus: %s has no placement in the catalogue", s.Node)
+		return b, fmt.Errorf("frombus: %s has no placement in the catalogue", s.Node)
 	}
 
 	in := compose.Input{OverlayCIDR: mesh.OverlayCIDR, InternalSuffix: mesh.InternalSuffix, Authority: mesh.Authority,
@@ -279,18 +326,6 @@ func input(ctx context.Context, r Reader, mesh Mesh, s Scope, refuse func(module
 			in.Authority = delivery.AuthorityBundle(in.Authority, vault)
 		}
 	}
-	parse := parser(mesh)
-	read := func(module, digest string) (catalogue.Manifest, error) {
-		raw, err := r.Manifest(ctx, digest)
-		if err != nil {
-			return catalogue.Manifest{}, fmt.Errorf("frombus: the manifest of %s (digest %s): %w", module, digest, err)
-		}
-		man, err := parse(raw)
-		if err != nil {
-			return catalogue.Manifest{}, fmt.Errorf("frombus: the manifest of %s (digest %s) does not decode: %w", module, digest, err)
-		}
-		return man, nil
-	}
 	named := func(field *map[string]string, module, why string) {
 		if *field == nil {
 			*field = map[string]string{}
@@ -309,7 +344,7 @@ func input(ctx context.Context, r Reader, mesh Mesh, s Scope, refuse func(module
 		raw, err := r.Manifest(ctx, m.Manifest)
 		if err != nil {
 			// Not read is no refusal of the module: a bus that does not answer is waited out by the caller.
-			return compose.Input{}, fmt.Errorf("frombus: the manifest of %s (digest %s): %w", name, m.Manifest, err)
+			return b, fmt.Errorf("frombus: the manifest of %s (digest %s): %w", name, m.Manifest, err)
 		}
 		// One module's manifest the indexer refused refuses that module alone, by the rule a build that cannot be read
 		// follows (issue 774: power's bar item refused every node's composition, 2026-10-30; ADR 0578 §3: one refused
@@ -318,8 +353,8 @@ func input(ctx context.Context, r Reader, mesh Mesh, s Scope, refuse func(module
 		man, why := taken(name, raw, m)
 		if why != "" {
 			named(&in.Refused, name, why)
-			if refuse != nil && ownPlaced[name] {
+			if ownPlaced[name] {
-				refuse(name, errors.New(why))
+				b.ownRefused = append(b.ownRefused, [2]string{name, why})
 			}
 		} else if aside := man.SetAside(); aside != "" {
 			named(&in.SetAside, name, aside)
@@ -332,11 +367,11 @@ func input(ctx context.Context, r Reader, mesh Mesh, s Scope, refuse func(module
 	for _, name := range delivery.ProvidedModules() {
 		raw, err := json.Marshal(overlay.Manifest())
 		if err != nil {
-			return compose.Input{}, err
+			return b, err
 		}
 		var private catalogue.Manifest
 		if err := json.Unmarshal(raw, &private); err != nil {
-			return compose.Input{}, fmt.Errorf("frombus: the manifest mesh-sdk provides for %s: %w", name, err)
+			return b, fmt.Errorf("frombus: the manifest mesh-sdk provides for %s: %w", name, err)
 		}
 		in.Catalogue[name] = private
 	}
@@ -357,13 +392,13 @@ func input(ctx context.Context, r Reader, mesh Mesh, s Scope, refuse func(module
 			var values map[string]any
 			if withValues {
 				if values, err = r.Values(ctx, node, m.Module); err != nil {
-					return compose.Input{}, fmt.Errorf("frombus: %s's config values on %s: %w", m.Module, node, err)
+					return b, fmt.Errorf("frombus: %s's config values on %s: %w", m.Module, node, err)
 				}
 			} else if keys := catalogue.ServedSettings(in.Catalogue[m.Module]); len(keys) > 0 {
 				// What a provider elsewhere serves from its settings is told to every consumer: the composing node reads
 				// those keys of it, and no other (issue 1126: mailu's smtp domain, a consumer's on shanks).
 				if values, err = r.Served(ctx, node, m.Module, keys); err != nil {
-					return compose.Input{}, fmt.Errorf("frombus: what %s serves on %s (%s): %w", m.Module, node,
+					return b, fmt.Errorf("frombus: what %s serves on %s (%s): %w", m.Module, node,
 						strings.Join(keys, ", "), err)
 				}
 			}
@@ -436,14 +471,35 @@ func input(ctx context.Context, r Reader, mesh Mesh, s Scope, refuse func(module
 		in.CarriedPeers = carriedPeers(in.Adopted.Tunnel, placements[in.Adopted.Hub].Decided.PeerNames, records)
 	}
 	if len(missing) > 0 {
-		return compose.Input{}, fmt.Errorf("frombus: modules are placed on %s, whose agent has written no record yet",
+		return b, fmt.Errorf("frombus: modules are placed on %s, whose agent has written no record yet",
 			strings.Join(missing, ", "))
 	}
+	b.in, b.placements, b.records, b.modules = in, placements, records, modules
+	return b, nil
+}
+
+// finish is input from its base on: the composing node's modules from their builds (build reads one), its own secrets.
+// in is the base's input, or a copy of it (base.cloned) where one base is finished more than once.
+func (b base) finish(ctx context.Context, r Reader, build func(ctx context.Context, module, fp string) (*delivery.BuilderBuild, error),
+	mesh Mesh, s Scope, in compose.Input, refuse func(module string, err error), wanted map[string]string) (compose.Input, error) {
+	var err error
+	parse := parser(mesh)
+	read := func(module, digest string) (catalogue.Manifest, error) {
+		raw, err := r.Manifest(ctx, digest)
+		if err != nil {
+			return catalogue.Manifest{}, fmt.Errorf("frombus: the manifest of %s (digest %s): %w", module, digest, err)
+		}
+		man, err := parse(raw)
+		if err != nil {
+			return catalogue.Manifest{}, fmt.Errorf("frombus: the manifest of %s (digest %s) does not decode: %w", module, digest, err)
+		}
+		return man, nil
+	}
 	if !s.Every {
-		if _, ok := records[s.Node]; !ok {
+		if _, ok := b.records[s.Node]; !ok {
 			return compose.Input{}, fmt.Errorf("frombus: %s has written no record of itself yet", s.Node)
 		}
-		if err := fromBuilds(ctx, r, &in, s, placements[s.Node], modules, read, parse, refuse, wanted); err != nil {
+		if err := fromBuilds(ctx, r, build, &in, s, b.placements[s.Node], b.modules, read, parse, refuse, wanted); err != nil {
 			return compose.Input{}, err
 		}
 		// Its own modules' secrets, sealed to its own key by the vault: a composition carries them sealed (ADR 0550 §5).
@@ -603,15 +659,8 @@ func PlansOf(in compose.Input, node string) (map[string]catalogue.Plan, error) {
 
 // plansIn is the controller's handedPlans in a mode: Foreseeing is the controller's own.
 func plansIn(in compose.Input, node string, mode compose.Mode) (map[string]catalogue.Plan, error) {
-	resolved, err := compose.Resolve(in, node)
+	// One composition for the three, so each node of the mesh is resolved once (issue 1954).
-	if err != nil {
+	resolved, rendered, gens, err := compose.Composing(in, node, mode)
-		return nil, fmt.Errorf("frombus: the plans of %s: %w", node, err)
-	}
-	rendered, err := compose.Render(in, node, mode)
-	if err != nil {
-		return nil, fmt.Errorf("frombus: the plans of %s: %w", node, err)
-	}
-	gens, err := compose.Generators(in)
 	if err != nil {
 		return nil, fmt.Errorf("frombus: the plans of %s: %w", node, err)
 	}
@@ -673,7 +722,8 @@ func ranOf(ctx context.Context, r Reader, mesh Mesh, running []delivery.Composed
 // module it keeps at another build (Scope.KeptAt, into its node's Kept), read from the builder's done key and resolved
 // by the one take-in rule (takein.Manifest), a templates archive read in the artifact store as the node reaches it
 // (issue 1126).
-func fromBuilds(ctx context.Context, r Reader, in *compose.Input, s Scope, p delivery.Placement, modules map[string]delivery.Module,
+func fromBuilds(ctx context.Context, r Reader, build func(ctx context.Context, module, fp string) (*delivery.BuilderBuild, error),
+	in *compose.Input, s Scope, p delivery.Placement, modules map[string]delivery.Module,
 	read func(module, digest string) (catalogue.Manifest, error), parse func([]byte) (catalogue.Manifest, error),
 	refuse func(module string, err error), wanted map[string]string) error {
 	// stub keeps a refused module in the composition as a stub for this node alone (compose.Stub): what it provides
@@ -716,6 +766,24 @@ func fromBuilds(ctx context.Context, r Reader, in *compose.Input, s Scope, p del
 		if b.Manifest == "" {
 			return catalogue.Manifest{}, fmt.Errorf("frombus: the build of %s at %s names no manifest", module, fp)
 		}
+		// A take-in kept by the reader is read back as below, never shared: each composition holds its own manifest.
+		keeper, keeps := r.(takenInKeeper)
+		if keeps && !addressed {
+			address, addressErr = compose.ArtifactStoreAddress(*in, s.Node)
+			addressed = true
+		}
+		// Kept by the store's address too: a node that reaches no store takes in as before, and fails where it did.
+		key, keyed := takenInKey(module, fp, address, *b)
+		keyed = keyed && addressErr == nil && address != ""
+		if keeps && keyed {
+			if raw, ok := keeper.takenIn(key); ok {
+				resolved, err := parse(raw)
+				if err != nil {
+					return catalogue.Manifest{}, fmt.Errorf("frombus: the built manifest of %s at %s: %w", module, fp, err)
+				}
+				return resolved, nil
+			}
+		}
 		src, err := read(module, b.Manifest)
 		if err != nil {
 			return catalogue.Manifest{}, err
@@ -733,6 +801,9 @@ func fromBuilds(ctx context.Context, r Reader, in *compose.Input, s Scope, p del
 		if resolved, err = parse(raw); err != nil {
 			return catalogue.Manifest{}, fmt.Errorf("frombus: the built manifest of %s at %s: %w", module, fp, err)
 		}
+		if keeps && keyed {
+			keeper.keepTakenIn(key, raw)
+		}
 		return resolved, nil
 	}
 	// A module wanted at another build than the trunk's is composed from the build its want names (issue 774), as one
@@ -766,7 +837,7 @@ func fromBuilds(ctx context.Context, r Reader, in *compose.Input, s Scope, p del
 		if man, ok := in.Catalogue[pm.Module]; !ok || (man.Build == nil && !man.Templated()) {
 			continue // nothing is built of it: its manifest is what it composes from
 		}
-		b, err := r.Build(ctx, pm.Module, m.FP2)
+		b, err := build(ctx, pm.Module, m.FP2)
 		if err != nil {
 			err = fmt.Errorf("frombus: the build of %s at %s: %w", pm.Module, m.FP2, err)
 			if refuse == nil {
@@ -801,7 +872,7 @@ func fromBuilds(ctx context.Context, r Reader, in *compose.Input, s Scope, p del
 		}
 		for _, module := range sortedKeys(keptAt) {
 			fp := keptAt[module]
-			b, err := r.Build(ctx, module, fp)
+			b, err := build(ctx, module, fp)
 			switch {
 			case err != nil:
 				err = fmt.Errorf("frombus: the build of %s at %s: %w", module, fp, err)

go/compose/frombus/frombustest/frombustest_test.go

@@ -2,10 +2,12 @@ package frombustest
 
 import (
 	"context"
+	"reflect"
 	"strings"
 	"testing"
 
 	stdio "git.novox.be/novox/mesh-sdk/go"
+	"git.novox.be/novox/mesh-sdk/go/catalogue"
 	"git.novox.be/novox/mesh-sdk/go/compose/frombus"
 	"git.novox.be/novox/mesh-sdk/go/compose/fromruntime"
 	"git.novox.be/novox/mesh-sdk/go/delivery"
@@ -117,6 +119,18 @@ func TestTheProvisionedMeshHandsAPlanWithItsProvision(t *testing.T) {
 			restic.Provisions[0].Provider != Node || restic.Provisions[0].ProviderModule != "postgres" {
 			t.Fatalf("%s: the plans are %+v (held %v)", row.name, plans, held)
 		}
+		// Issue 1954: the plans at the wanted builds and at the newest, over one read, are what PlansHeld answers for each,
+		// and where the time went is said by phase.
+		keptAt := FPs()
+		at, newest, took := frombus.PlansHeldTwice(context.Background(), b, frombus.Mesh{}, frombus.Scope{Node: Node, KeptAt: keptAt})
+		wantAt, heldAt, errAt := frombus.PlansHeld(context.Background(), b, frombus.Mesh{}, frombus.Scope{Node: Node, KeptAt: keptAt})
+		if !reflect.DeepEqual(at, frombus.HeldPlans{Plans: wantAt, Held: heldAt, Err: errAt}) ||
+			!reflect.DeepEqual(newest, frombus.HeldPlans{Plans: plans, Held: held}) {
+			t.Errorf("%s: twice composed %+v and %+v, want %v %v %v and %v %v", row.name, at, newest, wantAt, heldAt, errAt, plans, held)
+		}
+		if said := frombus.PhasesSaid(took); !strings.HasPrefix(said, "read ") || !strings.Contains(said, "plans at newest ") {
+			t.Errorf("%s: the phases are said as %q", row.name, said)
+		}
 		if row.bad == "" || row.elsewhere {
 			if len(held) > 0 {
 				t.Errorf("%s: held %v", row.name, held)
@@ -167,6 +181,85 @@ func TestTheProvisionedMeshHandsAPlanWithItsProvision(t *testing.T) {
 	if fetched != 1 {
 		t.Errorf("a templates archive was fetched %d times, want once", fetched)
 	}
+
+	// Issue 1954: the states reader takes a build in once per its content: composed again, its archive is not read again
+	// and the plans are the same.
+	b, err := Provisioned()
+	if err != nil {
+		t.Fatal(err)
+	}
+	reader, archives := frombus.StatesReader(statesOf(t, b), func(_ context.Context, url string) ([]byte, error) {
+		fetched++
+		_, digest, _ := strings.Cut(url, "/blobs/")
+		return b.Archives[digest], nil
+	}), fetched
+	var first map[string]catalogue.Plan
+	for i := range 2 {
+		plans, held, err := frombus.PlansHeld(context.Background(), reader, frombus.Mesh{}, frombus.Scope{Node: Node})
+		if err != nil || len(held) > 0 || (i == 1 && !reflect.DeepEqual(plans, first)) || !planned(plans, "restic") {
+			t.Fatalf("composed %v (held %v): %v", plans, held, err)
+		}
+		first = plans
+	}
+	if fetched-archives != 1 {
+		t.Errorf("restic's archive was read %d times over two compositions, want once", fetched-archives)
+	}
+}
+
+// statesOf is the bus b as a module's read states hold it.
+func statesOf(t *testing.T, b *Bus) frombus.States {
+	t.Helper()
+	s := states{}
+	put := func(state, key string, raw []byte, err error) {
+		if err != nil {
+			t.Fatal(err)
+		}
+		if s[state] == nil {
+			s[state] = map[string][]byte{}
+		}
+		s[state][key] = raw
+	}
+	for node, p := range b.Placement {
+		raw, err := delivery.EncodePlacement(p)
+		put(frombus.PlacementRead, "placement."+node, raw, err)
+	}
+	for node, rec := range b.Record {
+		raw, err := delivery.EncodeHaveNode(delivery.HaveNode{Record: &rec})
+		put(frombus.HaveRead, node+".node", raw, err)
+	}
+	for module, m := range b.Module {
+		key, _ := delivery.ModulesKey(module)
+		raw, err := delivery.EncodeModule(m)
+		put(frombus.ModulesRead, key, raw, err)
+	}
+	for digest, man := range b.Manifests {
+		key, _ := delivery.ManifestsKey(digest)
+		raw, err := delivery.EncodeManifest(delivery.Manifest{Module: "m", JSON: string(man)})
+		put(frombus.ManifestsRead, key, raw, err)
+	}
+	for at, build := range b.Builds {
+		module, fp, _ := strings.Cut(at, " ")
+		key, _ := delivery.BuilderBuildKey(module, fp)
+		raw, err := delivery.EncodeBuilderBuild(*build)
+		put(frombus.BuildsRead, key, raw, err)
+	}
+	return s
+}
+
+// states are read states in memory.
+type states map[string]map[string][]byte
+
+func (s states) Get(state, key string) ([]byte, bool, error) {
+	v, ok := s[state][key]
+	return v, ok, nil
+}
+
+func (s states) Keys(state string) ([]string, error) {
+	var keys []string
+	for k := range s[state] {
+		keys = append(keys, k)
+	}
+	return keys, nil
 }
 
 func planned[P any](plans map[string]P, module string) bool { _, ok := plans[module]; return ok }

go/compose/frombus/states.go

@@ -43,13 +43,22 @@ type States interface {
 type Fetch func(ctx context.Context, url string) ([]byte, error)
 
 // StatesReader is the Reader over s; fetch reads a templates archive, nil for a holder that reads none.
-func StatesReader(s States, fetch Fetch) Reader { return statesReader{s: s, fetch: fetch} }
+// It keeps what each build's take-in made, by the build's content (issue 1954), so a holder composing again and again
+// takes in only a build it has not seen.
+func StatesReader(s States, fetch Fetch) Reader {
+	return statesReader{s: s, fetch: fetch, kept: &keptTakeIns{}}
+}
 
 type statesReader struct {
 	s     States
 	fetch Fetch
+	kept  *keptTakeIns
 }
 
+func (r statesReader) takenIn(key string) ([]byte, bool) { return r.kept.takenIn(key) }
+
+func (r statesReader) keepTakenIn(key string, raw []byte) { r.kept.keepTakenIn(key, raw) }
+
 func (r statesReader) each(read string, visit func(key string, value []byte)) error {
 	keys, err := r.s.Keys(read)
 	if err != nil {

go/compose/frombus/twice.go

@@ -0,0 +1,147 @@
+package frombus
+
+// **A node's plans at two sets of builds, over one read** (issue 1954; novox/hq ADR 0570 clause 2, ADR 0580 clause 2):
+// the seat mesh-provisioner's holder composes each node at the builds its wants name and at the newest build of each
+// placed module. Both are composed from one read of the bus (placement, records, the indexer's modules and manifests,
+// values: base); only the builds the node's modules are composed from differ, each build read once for both, and a
+// build taken in once per content by a reader that keeps it (StatesReader). Where the time went is said by phase.
+
+import (
+	"context"
+	"crypto/sha256"
+	"encoding/hex"
+	"encoding/json"
+	"fmt"
+	"sync"
+	"time"
+
+	"git.novox.be/novox/mesh-sdk/go/catalogue"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// HeldPlans is one scope's plans, as PlansHeld answers them: err a refusal that is no single module's.
+type HeldPlans struct {
+	Plans map[string]catalogue.Plan
+	Held  map[string]string
+	Err   error
+}
+
+// Phase is one step of a composition and how long it took.
+type Phase struct {
+	Name string        `json:"phase"`
+	Took time.Duration `json:"took"`
+}
+
+// PlansHeldTwice is PlansHeld at s and at s with no kept builds (each placed module at its newest build), over one
+// read of the bus: what each answers is what PlansHeld answers for that scope. A read that fails is both scopes' err.
+// took names each phase in order: the read, then each scope's builds and its plans.
+func PlansHeldTwice(ctx context.Context, r Reader, mesh Mesh, s Scope) (at, newest HeldPlans, took []Phase) {
+	start := time.Now()
+	mark := func(name string) {
+		now := time.Now()
+		took = append(took, Phase{Name: name, Took: now.Sub(start)})
+		start = now
+	}
+	b, err := readBase(ctx, r, mesh, s)
+	mark("read")
+	builds := onceBuilds(r)
+	newestScope := s
+	newestScope.KeptAt = nil
+	for _, sc := range []struct {
+		scope Scope
+		into  *HeldPlans
+		name  string
+	}{{s, &at, "wanted"}, {newestScope, &newest, "newest"}} {
+		held := map[string]string{}
+		sc.into.Held = held
+		refuse := func(module string, err error) { held[module] = err.Error() }
+		b.refuseOwn(refuse)
+		if err != nil {
+			sc.into.Err = err
+			continue
+		}
+		in, err := b.finish(ctx, r, builds, mesh, sc.scope, b.cloned(), refuse, nil)
+		mark("builds at " + sc.name)
+		if err != nil {
+			sc.into.Err = err
+			continue
+		}
+		sc.into.Plans, sc.into.Err = plansHeldOf(in, s.Node, held)
+		mark("plans at " + sc.name)
+	}
+	return at, newest, took
+}
+
+// onceBuilds is r's Build, each module's build at a fingerprint read once: both scopes of one composition read the
+// builds of the same moment.
+func onceBuilds(r Reader) func(ctx context.Context, module, fp string) (*delivery.BuilderBuild, error) {
+	type answer struct {
+		b   *delivery.BuilderBuild
+		err error
+	}
+	read := map[string]answer{}
+	return func(ctx context.Context, module, fp string) (*delivery.BuilderBuild, error) {
+		key := module + " " + fp
+		if a, ok := read[key]; ok {
+			return a.b, a.err
+		}
+		b, err := r.Build(ctx, module, fp)
+		read[key] = answer{b, err}
+		return b, err
+	}
+}
+
+// takenInKeeper is a Reader that keeps what a build's take-in made (StatesReader does): the resolved manifest's bytes,
+// by the content it was made from, so a composition made again on every change takes in only a build it has not seen.
+type takenInKeeper interface {
+	takenIn(key string) ([]byte, bool)
+	keepTakenIn(key string, raw []byte)
+}
+
+// takenInKey is what a take-in is made from: the artifact store's address and the build's record (its manifest's digest, its artifacts by digest), read
+// whole; an archive is checked against its digest on every read, so the same record takes in to the same bytes.
+func takenInKey(module, fp, address string, b delivery.BuilderBuild) (string, bool) {
+	raw, err := json.Marshal(b)
+	if err != nil {
+		return "", false
+	}
+	sum := sha256.Sum256(append([]byte(module+" "+fp+" "+address+" "), raw...))
+	return hex.EncodeToString(sum[:]), true
+}
+
+// takenInAtMost bounds the take-ins a reader keeps; past it they are emptied, which costs only a take-in again.
+const takenInAtMost = 512
+
+// keptTakeIns is a reader's kept take-ins.
+type keptTakeIns struct {
+	mu   sync.Mutex
+	kept map[string][]byte
+}
+
+func (k *keptTakeIns) takenIn(key string) ([]byte, bool) {
+	k.mu.Lock()
+	defer k.mu.Unlock()
+	raw, ok := k.kept[key]
+	return raw, ok
+}
+
+func (k *keptTakeIns) keepTakenIn(key string, raw []byte) {
+	k.mu.Lock()
+	defer k.mu.Unlock()
+	if k.kept == nil || len(k.kept) >= takenInAtMost {
+		k.kept = map[string][]byte{}
+	}
+	k.kept[key] = raw
+}
+
+// PhasesSaid says the phases in one line, each in milliseconds.
+func PhasesSaid(took []Phase) string {
+	out := ""
+	for i, p := range took {
+		if i > 0 {
+			out += ", "
+		}
+		out += fmt.Sprintf("%s %d ms", p.Name, p.Took.Milliseconds())
+	}
+	return out
+}

go/compose/network.go

@@ -27,6 +27,23 @@ type composer struct {
 	// unhostable is, from the last look at the rest of the mesh, each module assigned to another node that this
 	// composition finds that node cannot run: what it would have offered is missing here (issue 1126, probe #532).
 	unhostable []string
+
+	// What one composition looks at again and again, each worked out once over its Input, which it never changes (issue
+	// 1954: a node's plans resolved every machine of the mesh some two hundred times, 11.7 s of CPU for novox): who is
+	// on the private network, and the rest of the mesh as each node sees it.
+	onNetwork    []Node
+	onNetworkSet bool
+	rest         map[string]restOf
+	plans        map[string]planOf
+}
+
+// restOf is theRestOfTheMesh's answer for one excluded node, kept: what it found unhostable beside it.
+type restOf struct {
+	world      catalogue.World
+	passes     Passes
+	left       []LeftOut
+	unhostable []string
+	err        error
 }
 
 func newComposer(in Input) *composer { return &composer{in: in, seen: map[string]bool{}} }
@@ -249,6 +266,14 @@ func (c *composer) whereEveryoneIs() (map[string]string, error) {
 // same rule as network(), so its name and its address stay where the tunnel to it does (issue 1833); one without is not
 // counted, and said.
 func (c *composer) onTheNetwork() []Node {
+	if !c.onNetworkSet {
+		c.onNetwork, c.onNetworkSet = c.onTheNetworkNow(), true
+	}
+	return slices.Clone(c.onNetwork)
+}
+
+// onTheNetworkNow is onTheNetwork worked out: every placed machine's set resolved.
+func (c *composer) onTheNetworkNow() []Node {
 	var out []Node
 	for _, n := range c.in.sorted() {
 		if n.Place.Address == "" {

go/compose/render.go

@@ -35,6 +35,26 @@ func Render(in Input, node string, mode Mode) (Rendered, error) {
 	return newComposer(in).render(node, mode)
 }
 
+// Composing is Resolve, Render and Generators of one node over one composition, which resolves each node of the mesh
+// once for all three (issue 1954: three compositions resolved the mesh again each, 11.7 s for one node's plans). Each
+// answers as it does alone; the first refusal ends it, in that order, with what follows it empty.
+func Composing(in Input, node string, mode Mode) (Resolved, Rendered, map[string]catalogue.Generator, error) {
+	c := newComposer(in)
+	resolved, err := c.planFor(node)
+	if err != nil {
+		return Resolved{}, Rendered{}, nil, err
+	}
+	rendered, err := c.render(node, mode)
+	if err != nil {
+		return resolved, Rendered{}, nil, err
+	}
+	gens, err := c.generators()
+	if err != nil {
+		return resolved, rendered, nil, err
+	}
+	return resolved, rendered, gens, nil
+}
+
 func (c *composer) render(nodeName string, mode Mode) (Rendered, error) {
 	resolved, err := c.planFor(nodeName)
 	if err != nil {

go/compose/resolve.go

@@ -36,8 +36,46 @@ func Resolve(in Input, node string) (Resolved, error) {
 // IsUnresolvable reports whether err is a node's own set failing to compose, rather than the mesh being unable to answer.
 func IsUnresolvable(err error) bool { return unresolvable(err) }
 
-// planFor is the controller's planFor.
+// planFor is the controller's planFor, worked out once per node in one composition (issue 1954): each caller has its
+// own copy of what a caller may set (a need's fields, as Resolution.Compose sets its Serves), the rest only read.
 func (c *composer) planFor(nodeName string) (Resolved, error) {
+	p, ok := c.plans[nodeName]
+	if !ok {
+		p.resolved, p.err = c.planForNow(nodeName)
+		if c.plans == nil {
+			c.plans = map[string]planOf{}
+		}
+		c.plans[nodeName] = p
+	}
+	if p.err != nil {
+		return Resolved{}, p.err
+	}
+	return p.resolved.copied(), nil
+}
+
+// planOf is planFor's answer for one node, kept.
+type planOf struct {
+	resolved Resolved
+	err      error
+}
+
+// copied is r with its own needs, words and settings lists: what a caller may change of it.
+func (r Resolved) copied() Resolved {
+	out := r
+	out.Plan.Needs = slices.Clone(r.Plan.Needs)
+	out.Foreseen = slices.Clone(r.Foreseen)
+	out.NotGiven = slices.Clone(r.NotGiven)
+	if r.Settings != nil {
+		out.Settings = make(catalogue.SettingsBy, len(r.Settings))
+		for m, layers := range r.Settings {
+			out.Settings[m] = slices.Clone(layers)
+		}
+	}
+	return out
+}
+
+// planForNow is planFor worked out.
+func (c *composer) planForNow(nodeName string) (Resolved, error) {
 	resolved, err := c.resolution(nodeName)
 	if err != nil {
 		return Resolved{}, err

go/compose/rest.go

@@ -3,6 +3,7 @@ package compose
 import (
 	"errors"
 	"fmt"
+	"slices"
 	"sort"
 	"strings"
 
@@ -59,6 +60,22 @@ func TheRestOfTheMesh(in Input, exclude string) (catalogue.World, Passes, []Left
 }
 
 func (c *composer) theRestOfTheMesh(exclude string) (catalogue.World, Passes, []LeftOut, error) {
+	r, ok := c.rest[exclude]
+	if !ok {
+		r.world, r.passes, r.left, r.err = c.theRestOfTheMeshNow(exclude)
+		r.unhostable = c.unhostable
+		if c.rest == nil {
+			c.rest = map[string]restOf{}
+		}
+		c.rest[exclude] = r
+	}
+	// Each caller has its own copy of what it may set or add to; the maps and the slices within are only read.
+	c.unhostable = slices.Clone(r.unhostable)
+	return r.world, r.passes, slices.Clone(r.left), r.err
+}
+
+// theRestOfTheMeshNow is theRestOfTheMesh worked out: every other machine's set resolved, twice.
+func (c *composer) theRestOfTheMeshNow(exclude string) (catalogue.World, Passes, []LeftOut, error) {
 	shelf := c.in.Catalogue
 	holdings := append([]catalogue.Held(nil), c.in.Holdings...)
 	nodes := c.in.sorted()

go/state_test.go

@@ -283,4 +283,24 @@ func TestABundleKeepsAndWatchesStateThroughTheRuntime(t *testing.T) {
 	if gets != 3 {
 		t.Fatalf("a kept value was read by key %d times, want once, and the missing one twice", gets)
 	}
+	// Issue 1954: a state the process alone writes reads its own put and delete back from the copy at once, and the
+	// watch's changes of that key up to the write are not taken over it; a later change is.
+	_ = handles["placement"](StateChange{Key: "own", Op: OpPut, Value: []byte("old"), Revision: 5})
+	if err := w.Wrote("placement", "own", []byte("mine"), 7); err != nil {
+		t.Fatal(err)
+	}
+	_ = w.Wrote("placement", "gone", []byte("x"), 8)
+	_ = w.Removed("placement", "gone")
+	for _, c := range []StateChange{{Key: "own", Op: OpPut, Value: []byte("old"), Revision: 6},
+		{Key: "own", Op: OpPut, Value: []byte("mine"), Revision: 7}, {Key: "gone", Op: OpPut, Value: []byte("x"), Revision: 8}} {
+		_ = handles["placement"](c)
+	}
+	own, _, _ := w.Get("placement", "own")
+	if _, found, _ := w.Get("placement", "gone"); found || string(own) != "mine" {
+		t.Fatalf("after its own writes and the watch's older changes the copy holds own=%s, gone found %v", own, found)
+	}
+	_ = handles["placement"](StateChange{Key: "gone", Op: OpPut, Value: []byte("again"), Revision: 9})
+	if v, _, _ := w.Get("placement", "gone"); string(v) != "again" {
+		t.Fatalf("a change after its own delete is not taken: %s", v)
+	}
 }

go/watched.go

@@ -33,6 +33,10 @@ type watchedState struct {
 
 	mu     sync.Mutex
 	values map[string][]byte
+	// revs is, by key, the revision its value in the copy is at, and latest the highest revision the copy has seen: a
+	// change the watch hands at a revision not newer than its key's is one the copy already took (Wrote, Removed).
+	revs    map[string]uint64
+	latest  uint64
 	then    []func(StateChange) error
 	started bool          // the current values are in, so a change runs then at once
 	pending []StateChange // the current values, run through then once all are in
@@ -77,7 +81,7 @@ func (w *WatchedStates) watched(state string, then func(StateChange) error) (*wa
 		}
 		return s, nil
 	}
-	s = &watchedState{ready: make(chan struct{}), values: map[string][]byte{}}
+	s = &watchedState{ready: make(chan struct{}), values: map[string][]byte{}, revs: map[string]uint64{}}
 	if then != nil {
 		s.then = []func(StateChange) error{then}
 	}
@@ -85,11 +89,17 @@ func (w *WatchedStates) watched(state string, then func(StateChange) error) (*wa
 	w.mu.Unlock()
 	err := w.watch(state, func(c StateChange) error {
 		s.mu.Lock()
-		if c.Op == OpPut {
+		switch {
+		case c.Revision != 0 && c.Revision <= s.revs[c.Key]:
+			// Already in the copy, or older than what is: this process wrote the key since (Wrote, Removed).
+		case c.Op == OpPut:
 			s.values[c.Key] = append([]byte(nil), c.Value...)
-		} else {
+			s.revs[c.Key] = c.Revision
+		default:
 			delete(s.values, c.Key)
+			s.revs[c.Key] = c.Revision
 		}
+		s.latest = max(s.latest, c.Revision)
 		if !s.started {
 			s.pending = append(s.pending, c)
 			s.mu.Unlock()
@@ -240,5 +250,44 @@ func (w *WatchedStates) Once(state, key string) ([]byte, bool, error) {
 	return v, true, nil
 }
 
+// Wrote takes a put this process made into the copy at once, at the revision the bus answered (0 when not known): a
+// state the process alone writes (a holder's own) is read back from the copy right after its own write, before the
+// watch hands the change back, and the watch's older changes of the key are not taken over it (issue 1954). The state
+// is watched first when it is not yet.
+func (w *WatchedStates) Wrote(state, key string, value []byte, revision uint64) error {
+	return w.took(state, key, value, revision, true)
+}
+
+// Removed takes a delete this process made into the copy at once, as Wrote takes a put.
+func (w *WatchedStates) Removed(state, key string) error { return w.took(state, key, nil, 0, false) }
+
+func (w *WatchedStates) took(state, key string, value []byte, revision uint64, put bool) error {
+	s, err := w.watched(state, nil)
+	if err != nil {
+		return err
+	}
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	switch {
+	case put && revision != 0:
+		if revision <= s.revs[key] {
+			return nil // the watch handed a newer change of the key already
+		}
+		s.values[key] = append([]byte(nil), value...)
+		s.revs[key] = revision
+		s.latest = max(s.latest, revision)
+	default:
+		// A delete's revision is not answered, nor a put's at times: it is newer than every revision the copy has seen,
+		// so the watch's changes of the key up to that one are not taken over it.
+		if put {
+			s.values[key] = append([]byte(nil), value...)
+		} else {
+			delete(s.values, key)
+		}
+		s.revs[key] = s.latest
+	}
+	return nil
+}
+
 // Direct is a key read by key now, not from the copy: a value that changes and is read one at a time (a build).
 func (w *WatchedStates) Direct(state, key string) ([]byte, bool, error) { return w.get(state, key) }