Merge pull request 'The assigner's verbs and the checker's tools ask the indexer's tools instead of reading its state (issue 1966, recovery)' (#176) from fix/1966-assigner-seat-reads into main

modules/mesh-delivery-assigner/cmd/mesh-delivery-assigner/pass_test.go

@@ -293,6 +293,9 @@ func (s memStore) put(state, key string, value []byte) error {
 	return nil
 }
 func (s memStore) keys(state string) ([]string, error) {
+	if s[state] == nil { // as the runtime refuses a state the module neither keeps nor reads
+		return nil, fmt.Errorf("mesh-delivery-assigner keeps and reads no state called %q", state)
+	}
 	var out []string
 	for k := range s[state].values {
 		out = append(out, k)
@@ -362,9 +365,14 @@ func putOfTheBus(t *testing.T) {
 
 	buildKV := mem()
 	buildKV.values[bkey] = built
-	modules := mem()
+	// Issue 1966: newest is asked of the indexer's first view of modules, never read from its bus state.
-	modules.values["nats"] = mod
+	indexer := &fakeIndexer{views: map[string]map[string][]byte{"mesh-delivery-indexer.modules": {"mesh-catalog": mod, "nats": mod}}}
-	s := newPutTools(memStore{putsState: putsKV, builds.BuilderModule + ".builds": buildKV, buckets.IndexerModule + ".modules": modules})
+	s := newPutTools(memStore{putsState: putsKV, builds.BuilderModule + ".builds": buildKV}, func(key string, body any) (json.RawMessage, error) {
+		if raw, ok, err := indexer.answer(key, body); ok {
+			return raw, err
+		}
+		return nil, fmt.Errorf("%s is not served here", key)
+	})
 	s.now = func() time.Time { return now }
 	was := answerWithin
 	answerWithin = 0
@@ -375,8 +383,11 @@ func putOfTheBus(t *testing.T) {
 	if got, err := s.version("nats", "fd497ab80000"); err != nil || got != fp {
 		t.Errorf("the prefix of the fingerprint built reads %q, %v", got, err)
 	}
-	if got, err := s.version("nats", "newest"); err != nil || got != fp {
+	if got, err := s.version("nats", "newest"); err != nil || got != fp || indexer.asks["mesh-delivery-indexer.modules"] != 2 {
-		t.Errorf("newest reads %q, %v", got, err)
+		t.Errorf("newest reads %q, %v, asking %d pages of the indexer's first view (want its 2)", got, err, indexer.asks["mesh-delivery-indexer.modules"])
+	}
+	if _, err := s.version("ghost", "newest"); err == nil || !strings.Contains(err.Error(), "holds no module ghost") {
+		t.Errorf("newest of a module the indexer does not hold: %v", err)
 	}
 	ans, err := s.doPut(map[string]any{"node": "novox", "module": "nats", "version": fp, "hold": "true", "why": "the bus's user list"}, "shanks.node-tools")
 	if err != nil {

modules/mesh-delivery-assigner/cmd/mesh-delivery-assigner/seat_tools.go

@@ -1,9 +1,11 @@
 package main
 
 import (
+	"context"
 	"encoding/json"
 	"errors"
 	"fmt"
+	"maps"
 	"mesh-delivery-assigner/internal/buckets"
 	"slices"
 	"sort"
@@ -17,6 +19,7 @@ import (
 	mmac "git.novox.be/novox/mesh-contracts/go/clients/meshmoduleassignerclient"
 	mma "git.novox.be/novox/mesh-contracts/go/seats/meshmoduleassigner"
 	stdio "git.novox.be/novox/mesh-sdk/go"
+	"git.novox.be/novox/mesh-sdk/go/views"
 
 	"mesh-delivery-assigner/internal/assign"
 	plc "mesh-delivery-assigner/internal/assignment"
@@ -42,12 +45,40 @@ func (runtimeStore) history(state, key string) ([]stdio.StateRevision, error) {
 }
 
 // The states the verbs read, as the runtime names them: the seat's own by their local names, the others'
-// `<module>.<state>`.
+// `<module>.<state>` where the manifest declares them under `reads`.
+const haveState = "node-engine.have"
+
+// The indexer's states the verbs read, each asked of the indexer's first-view tool of that name, never read from its bus
+// state (novox/hq ADR 0596; ADR 0615 §1, ADR 0621 §1, §2: the manifest invokes them, and the indexer answers them to the
+// assigner alone of the delivery's parts).
 const (
-	modulesState = buckets.IndexerModule + ".modules"
+	indexerModules   = "modules"
-	haveState    = "node-engine.have"
+	indexerManifests = "manifests"
 )
 
+// indexerView is one of the indexer's states whole, asked of its first-view tool through ask (stdio.Ask, or a test's) page
+// after page, each page continued after the one before's next. It is asked again at every call: the indexer's state is
+// the truth, and the verbs keep no copy of it.
+func indexerView(ask func(string, any) (json.RawMessage, error), state string) (map[string]json.RawMessage, error) {
+	tool := buckets.IndexerModule + "." + state
+	if ask == nil {
+		return nil, fmt.Errorf("%s cannot be asked here", tool)
+	}
+	page := views.AskVia(ask, tool)
+	out := map[string]json.RawMessage{}
+	for after := ""; ; {
+		a, err := page(context.Background(), after)
+		if err != nil {
+			return nil, fmt.Errorf("%s does not answer: %w", tool, err)
+		}
+		maps.Copy(out, a.Values)
+		if a.Next == "" || a.Next == after {
+			return out, nil
+		}
+		after = a.Next
+	}
+}
+
 // seatTools serves the seat's verbs over a store, asking the controller through ask (stdio.Ask, or a test's).
 type seatTools struct {
 	st  seatStore
@@ -97,14 +128,15 @@ func (s *seatTools) assignments() (map[string]mma.Assignments, map[string]uint64
 	return out, revs, nil
 }
 
-// lays is what a proposal is checked against: the modules the indexer holds and the nodes with a record.
+// lays is what a proposal is checked against: the modules the indexer holds, as its first view of modules answers them,
+// and the nodes with a record.
 func (s *seatTools) lays() (func(string) bool, func(string) bool, error) {
-	mods, err := s.st.keys(modulesState)
+	mods, err := indexerView(s.ask, indexerModules)
 	if err != nil {
 		return nil, nil, fmt.Errorf("the indexer's modules cannot be listed: %w", err)
 	}
 	held := map[string]bool{}
-	for _, k := range mods {
+	for k := range mods {
 		if name, err := meshcatalogclient.ParseModulesKey(k); err == nil {
 			held[name] = true
 		}

modules/mesh-delivery-assigner/cmd/mesh-delivery-assigner/seat_tools_test.go

@@ -26,6 +26,7 @@ import (
 	"git.novox.be/novox/mesh-contracts/provisioning/go/clients/meshprovisionerclient"
 	stdio "git.novox.be/novox/mesh-sdk/go"
 	"git.novox.be/novox/mesh-sdk/go/catalogue"
+	"git.novox.be/novox/mesh-sdk/go/views"
 	"github.com/nats-io/nats.go/jetstream"
 
 	"mesh-delivery-assigner/internal/assign"
@@ -52,11 +53,13 @@ func TestTheSeatsVerbs(t *testing.T) {
 	anchor := mma.Assignments{V: keys.Version, Node: "anchor", Modules: []mma.PlacedModule{{Module: "web"}, {Module: "mesh-enrolment"}},
 		Holds: []mma.Holding{{Claim: "mesh-node-enroller", Scope: "mesh", Module: "mesh-enrolment"}}}
 	st := memStore{}
-	for _, state := range []string{mma.StateAssignments, mma.StateProposals, mma.StateCandidates, modulesState, haveState} {
+	for _, state := range []string{mma.StateAssignments, mma.StateProposals, mma.StateCandidates, haveState} {
 		st[state] = &memKV{values: map[string][]byte{}}
 	}
+	// Issue 1966: the indexer's modules are asked of its first view, never read from its bus state (ADR 0596, ADR 0621).
+	indexer := &fakeIndexer{views: map[string]map[string][]byte{"mesh-delivery-indexer.modules": {}}}
 	for _, m := range []string{"web", "shell", "mesh-enrolment"} {
-		st[modulesState].values[m] = []byte("{}")
+		indexer.views["mesh-delivery-indexer.modules"][m] = []byte("{}")
 	}
 	for _, n := range []string{"anchor", "laptop"} {
 		raw, _ := nodeengineclient.EncodeHaveNode(nodeengine.HaveByNodeNodeValue{Record: &nodeengine.NodeRecord{Node: n}})
@@ -65,6 +68,9 @@ func TestTheSeatsVerbs(t *testing.T) {
 	var asked []string
 	s := newSeatTools(st, func(key string, body any) (json.RawMessage, error) {
 		asked = append(asked, key)
+		if raw, ok, err := indexer.answer(key, body); ok {
+			return raw, err
+		}
 		return json.RawMessage(`{"ok":true}`), nil
 	})
 	s.now = func() time.Time { return time.Date(2026, 10, 28, 20, 0, 0, 0, time.UTC) }
@@ -193,6 +199,32 @@ func TestTheSeatsVerbs(t *testing.T) {
 	if tools := s.tools(); len(tools) != 5 || tools[2].Name != "mesh-module-assigner.propose" || tools[2].Run == nil {
 		t.Errorf("the seat's verbs as served: %+v", tools)
 	}
+	// Issue 1966: propose checks its modules against the indexer's first view of modules, every page of it, asked again at
+	// each call; a first view the indexer refuses refuses the proposal, naming the tool, and writes nothing.
+	for _, c := range []struct {
+		name, module, refused, want string
+	}{
+		{"a module on the last page", "web", "", ""},
+		{"a module the indexer does not hold", "ghost", "", "ghost"},
+		{"the first view refused", "web", "mesh-delivery-indexer.modules", "mesh-delivery-indexer.modules does not answer"},
+	} {
+		t.Run("1966: "+c.name, func(t *testing.T) {
+			indexer.refused, indexer.asks = c.refused, nil
+			maps.DeleteFunc(st[mma.StateAssignments].values, func(k string, _ []byte) bool { return strings.HasPrefix(k, "joiner.") }) // the remove-node's joiner
+			st[mma.StateProposals].values, st[mma.StateCandidates].values = map[string][]byte{}, map[string][]byte{}
+			_, err := s.doPropose(map[string]any{"why": "x", "changes": []any{map[string]any{"op": "place", "node": "laptop", "module": c.module}}}, "op")
+			switch {
+			case c.want == "" && err != nil:
+				t.Errorf("propose: %v", err)
+			case c.want != "" && (err == nil || !strings.Contains(err.Error(), c.want) || len(st[mma.StateProposals].values) != 0):
+				t.Errorf("propose: %v, want a refusal saying %q and nothing written", err, c.want)
+			}
+			if pages := indexer.asks["mesh-delivery-indexer.modules"]; c.refused == "" && pages != 3 {
+				t.Errorf("the first view of modules was asked %d pages, want its 3", pages)
+			}
+		})
+	}
+	indexer.refused = ""
 	t.Run("1953/D4-D6: the seat mesh-wants' upgrade and bus", wantsVerbs)
 	t.Run("1955/L7 (ADR 0571 §6): rule 7 reads the node's own composition; an unplaced node is said", func(t *testing.T) {
 		w := newWorld()
@@ -439,9 +471,11 @@ func TestTheSeatsVerbs(t *testing.T) {
 func wantsVerbs(t *testing.T) {
 	fpOld, fpNew := meshcatalogclient.SourcePrefix2+strings.Repeat("1", 64), meshcatalogclient.SourcePrefix2+strings.Repeat("2", 64)
 	st := memStore{}
-	for _, state := range []string{modulesState, manifestsState, policiesState, haveState, putsState, "findings", buckets.ComposedRead} {
+	for _, state := range []string{policiesState, haveState, putsState, "findings", buckets.ComposedRead} {
 		st[state] = &memKV{values: map[string][]byte{}}
 	}
+	// Issue 1966: the indexer's modules and manifests are asked of its first views, never read from its bus state.
+	indexer := &fakeIndexer{views: map[string]map[string][]byte{"mesh-delivery-indexer.modules": {}, "mesh-delivery-indexer.manifests": {}}}
 	// ADR 0593 §6, §8: what each node published, every node's bucket as one state: anchor's own composition and its web at
 	// a fingerprint, and laptop's web refused there.
 	partNew, _ := meshcatalogclient.KeyPart(fpNew)
@@ -453,8 +487,8 @@ func wantsVerbs(t *testing.T) {
 	manifest := func(name, extra string) {
 		raw := `{"module":"` + name + `","version":"1"` + extra + `}`
 		digest := meshcatalogclient.ManifestDigest([]byte(raw))
-		st[manifestsState].values[digest], _ = meshcatalogclient.EncodeManifest(meshcatalog.ManifestsByDigestValue{V: keys.Version, Module: name, Manifest: raw})
+		indexer.views["mesh-delivery-indexer.manifests"][digest], _ = meshcatalogclient.EncodeManifest(meshcatalog.ManifestsByDigestValue{V: keys.Version, Module: name, Manifest: raw})
-		st[modulesState].values[name], _ = meshcatalogclient.EncodeModule(meshcatalog.ModulesByModuleValue{V: keys.Version, Fp2: fpNew, Manifest: digest, Repository: "novox/x", Commit: "c"})
+		indexer.views["mesh-delivery-indexer.modules"][name], _ = meshcatalogclient.EncodeModule(meshcatalog.ModulesByModuleValue{V: keys.Version, Fp2: fpNew, Manifest: digest, Repository: "novox/x", Commit: "c"})
 	}
 	manifest("web", "")
 	manifest("photos", `,"upgrade":{"policy":"record","why":"a person checks the albums"}`)
@@ -465,10 +499,14 @@ func wantsVerbs(t *testing.T) {
 	st[haveState].values["anchor.node"], _ = nodeengineclient.EncodeHaveNode(nodeengine.HaveByNodeNodeValue{Composed: "sha256:" + strings.Repeat("c", 64)})
 	var asked []string
 	var said []string
-	w := newWantsTools(st, func(key string, body any) (json.RawMessage, error) {
+	ask := func(key string, body any) (json.RawMessage, error) {
 		asked = append(asked, key)
+		if raw, ok, err := indexer.answer(key, body); ok {
+			return raw, err
+		}
 		return json.RawMessage(`{"ok":true}`), nil
-	}, func(event, id string, body any) error { said = append(said, event+" "+id); return nil })
+	}
+	w := newWantsTools(st, ask, func(event, id string, body any) error { said = append(said, event+" "+id); return nil })
 	policyOf := func(module string) policyRow {
 		out, err := w.doUpgrade(map[string]any{"module": module}, "op")
 		if err != nil {
@@ -497,7 +535,7 @@ func wantsVerbs(t *testing.T) {
 	// Read by watch (issue 1953 L5f): the same answer, each watched state started once, and no get per key of the
 	// large states (the modules, their manifests, the composed record).
 	watches := map[string]int{}
-	byWatch := newWantsTools(st, nil, nil)
+	byWatch := newWantsTools(st, ask, nil)
 	byWatch.watched = stdio.WatchedStatesOver(func(state string, handle func(stdio.StateChange) error) error {
 		watches[state]++
 		for k, v := range st[state].values {
@@ -518,10 +556,13 @@ func wantsVerbs(t *testing.T) {
 			t.Errorf("compare by watch = %+v", got)
 		}
 	}
-	if n := watches[manifestsState+" by key"]; n == 0 || n > len(st[manifestsState].values) {
+	for _, state := range []string{"mesh-delivery-indexer.modules", "mesh-delivery-indexer.manifests"} {
-		t.Errorf("the manifests were read by key %d times, want each once", n)
+		if watches[state] != 0 || watches[state+" by key"] != 0 || indexer.asks[state] == 0 {
+			t.Errorf("the indexer's %s was watched %d times and read by key %d, asked of its first view %d times: want asked alone",
+				state, watches[state], watches[state+" by key"], indexer.asks[state])
+		}
 	}
-	for _, state := range []string{modulesState, haveState, mcc.FindingsState} {
+	for _, state := range []string{haveState, mcc.FindingsState} {
 		if watches[state] != 1 {
 			t.Errorf("%s was watched %d times, want once", state, watches[state])
 		}
@@ -742,3 +783,42 @@ func (k *copiesKV) Put(_ context.Context, key string, value []byte) (uint64, err
 	k.values[key] = value
 	return uint64(len(k.values)), nil
 }
+
+// fakeIndexer answers the indexer's first-view tools as its runtime does (views.FirstViewTool): each tool its state's values
+// in key order, one key a page, each page continued after the page before's next; the tool named refused answers its
+// refusal. asks counts the pages asked by tool.
+type fakeIndexer struct {
+	views   map[string]map[string][]byte
+	refused string
+	asks    map[string]int
+}
+
+// answer is the answer to a call of key, and whether key is one of the indexer's first views at all.
+func (f *fakeIndexer) answer(key string, body any) (json.RawMessage, bool, error) {
+	values, ok := f.views[key]
+	if !ok {
+		return nil, false, nil
+	}
+	if f.asks == nil {
+		f.asks = map[string]int{}
+	}
+	f.asks[key]++
+	if key == f.refused {
+		return nil, true, fmt.Errorf("%s is refused to \"novox.mesh-delivery-assigner\"", key)
+	}
+	after, _ := body.(map[string]any)["after"].(string)
+	a := views.Answer{V: views.Version, Owner: buckets.IndexerModule, State: strings.TrimPrefix(key, buckets.IndexerModule+"."), Revision: 7,
+		Values: map[string]json.RawMessage{}}
+	for _, k := range slices.Sorted(maps.Keys(values)) {
+		if k <= after {
+			continue
+		}
+		if len(a.Values) == 1 {
+			a.Next = slices.Collect(maps.Keys(a.Values))[0]
+			break
+		}
+		a.Values[k] = values[k]
+	}
+	raw, err := json.Marshal(a)
+	return raw, true, err
+}

modules/mesh-delivery-assigner/cmd/mesh-delivery-assigner/tools.go

@@ -4,7 +4,6 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
-	"mesh-delivery-assigner/internal/buckets"
 	"mesh-delivery-assigner/internal/puts"
 	"os"
 	"regexp"
@@ -45,7 +44,9 @@ type store interface {
 
 // putTools serves the tools over a store, and keeps the newest value of every put it heard, to wait on.
 type putTools struct {
-	st  store
+	st store
+	// ask asks a module's tool (stdio.Ask, or a test's): the indexer's first view of modules for newest.
+	ask func(key string, body any) (json.RawMessage, error)
 	now func() time.Time
 	mu  sync.Mutex
 	// heard is every put the watch handed, by key; changed is closed and replaced at each.
@@ -53,8 +54,8 @@ type putTools struct {
 	changed chan struct{}
 }
 
-func newPutTools(st store) *putTools {
+func newPutTools(st store, ask func(string, any) (json.RawMessage, error)) *putTools {
-	return &putTools{st: st, now: time.Now, heard: map[string][]byte{}, changed: make(chan struct{})}
+	return &putTools{st: st, ask: ask, now: time.Now, heard: map[string][]byte{}, changed: make(chan struct{})}
 }
 
 // hear takes a put's change in from the watch.
@@ -78,10 +79,12 @@ func (s *putTools) version(module, version string) (string, error) {
 	v := strings.ToLower(strings.TrimSpace(version))
 	switch {
 	case v == "newest":
-		raw, _, found, err := s.st.get(buckets.ModulesRead, module)
+		// Asked of the indexer's first view of modules, never read from its bus state (ADR 0596, ADR 0621; issue 1966).
+		mods, err := indexerView(s.ask, indexerModules)
 		if err != nil {
 			return "", fmt.Errorf("the indexer's modules cannot be read: %w", err)
 		}
+		raw, found := mods[module]
 		if !found {
 			return "", fmt.Errorf("the indexer holds no module %s at the trunk", module)
 		}
@@ -345,7 +348,7 @@ func (runtimeStore) keys(state string) ([]string, error) { return stdio.State(st
 
 // serveTools serves the tools to the runtime until it stops, hearing every put to answer assigner_put with its first steps.
 func serveTools() error {
-	s := newPutTools(runtimeStore{})
+	s := newPutTools(runtimeStore{}, stdio.Ask)
 	go func() {
 		<-stdio.Served()
 		for wait := 2 * time.Second; ; wait = min(wait*2, time.Minute) {

modules/mesh-delivery-assigner/cmd/mesh-delivery-assigner/wants_tools.go

@@ -32,8 +32,7 @@ import (
 
 // The states the verbs read, as the runtime names them.
 const (
-	policiesState  = buckets.PoliciesState
+	policiesState = buckets.PoliciesState
-	manifestsState = buckets.IndexerModule + ".manifests"
 	// PolicyChangedEvent is the seat's event of a person's policy set or taken back.
 	PolicyChangedEvent = "policy-changed"
 	// busStepCause is the cause the bus's step is recorded under in the hand-act log.
@@ -88,19 +87,14 @@ func (s *wantsTools) direct(state string) (map[string][]byte, error) {
 	return out, nil
 }
 
-// manifest reads a manifest by its digest: kept once read when there is a watched copy, a manifest never changing
+// manifests is every module the indexer holds, with its trunk manifest and fingerprint: both asked of the indexer's first
-// under its digest.
+// views of modules and manifests (indexerView), never read from its bus state.
-func (s *wantsTools) manifest(digest string) ([]byte, bool, error) {
-	if s.watched != nil {
-		return s.watched.Once(manifestsState, digest)
-	}
-	raw, _, found, err := s.st.get(manifestsState, digest)
-	return raw, found, err
-}
-
-// manifests is every module the indexer holds, with its trunk manifest and fingerprint.
 func (s *wantsTools) manifests() (map[string]catalogue.Manifest, map[string]meshcatalog.ModulesByModuleValue, error) {
-	mods, err := s.values(modulesState)
+	mods, err := indexerView(s.ask, indexerModules)
+	if err != nil {
+		return nil, nil, err
+	}
+	kept, err := indexerView(s.ask, indexerManifests)
 	if err != nil {
 		return nil, nil, err
 	}
@@ -114,16 +108,16 @@ func (s *wantsTools) manifests() (map[string]catalogue.Manifest, map[string]mesh
 		if m.Manifest == "" {
 			continue
 		}
-		mraw, found, err := s.manifest(m.Manifest)
+		mraw, found := kept[m.Manifest]
-		if err != nil || !found {
+		if !found {
 			continue
 		}
-		kept, err := meshcatalogclient.DecodeManifest(mraw)
+		stored, err := meshcatalogclient.DecodeManifest(mraw)
 		if err != nil {
 			continue
 		}
 		// Decoded, never judged (ADR 0578 §3); one that does not decode is left out of the answer, as before.
-		if man, err := catalogue.Decode([]byte(kept.Manifest)); err == nil {
+		if man, err := catalogue.Decode([]byte(stored.Manifest)); err == nil {
 			out[name] = man
 		}
 	}

modules/mesh-delivery-checker/cmd/mesh-delivery-checker-tools/main.go

@@ -1,6 +1,6 @@
 // Command mesh-delivery-checker-tools serves the checker's read tools (novox/hq ADR 0484 clause 13, issue 1686): the runtime
-// launches it for a call, it reads the checker's verdicts and kept states and the indexer's candidates through the checker's
+// launches it for a call, it reads the checker's verdicts and kept states through the checker's state and reads, and the
-// state and reads. It writes only the tries (the try's tools) and, asking a check again by hand, one verdict. The checker is the other program: it serves no tool (ADR 0437 §4).
+// indexer's candidates and modules through the indexer's read tools. It writes only the tries (the try's tools) and, asking a check again by hand, one verdict. The checker is the other program: it serves no tool (ADR 0437 §4).
 package main
 
 import (
@@ -18,6 +18,7 @@ import (
 	"git.novox.be/novox/mesh-delivery/contracts/go/seats/meshdeliverychecker"
 	"git.novox.be/novox/mesh-delivery/modules/mesh-delivery-builder/buildrun"
 	stdio "git.novox.be/novox/mesh-sdk/go"
+	"git.novox.be/novox/mesh-sdk/go/buscalls"
 	"git.novox.be/novox/mesh-sdk/go/views"
 )
 
@@ -58,6 +59,52 @@ func read(s stdio.KeptState) check.StateRead {
 	}}
 }
 
+// ownerRead is a state of another module read through that module's ordinary read tool (views.ReadTool), asked through ask
+// (stdio.Ask, or a test's): its keys with no argument, one key's value with key. Another module's data is asked through its
+// tools, never read from its bus state (novox/hq ADR 0596); the manifest invokes the tool, and the owner answers every reader
+// that invokes it. Each read is asked when it is read: the owner's state is the truth, and the tools keep no copy.
+func ownerRead(ask func(string, any) (json.RawMessage, error), tool string) check.StateRead {
+	call := func(args map[string]any, into any) error {
+		reads.Add(1)
+		raw, err := ask(tool, args)
+		if err != nil {
+			return fmt.Errorf("%s does not answer: %w", tool, err)
+		}
+		answer, said, ok := buscalls.Unwrap(raw)
+		if !ok {
+			return fmt.Errorf("%s answered: %s", tool, said)
+		}
+		if err := json.Unmarshal(answer, into); err != nil {
+			return fmt.Errorf("%s answered what does not decode: %w", tool, err)
+		}
+		return nil
+	}
+	return check.StateRead{
+		Keys: func() ([]string, error) {
+			var a views.ReadAnswer
+			if err := call(map[string]any{}, &a); err != nil {
+				return nil, err
+			}
+			return a.Keys, nil
+		},
+		Get: func(key string) (json.RawMessage, error) {
+			var a views.KeyAnswer
+			if err := call(map[string]any{"key": key}, &a); err != nil {
+				return nil, err
+			}
+			if !a.Found {
+				return nil, nil
+			}
+			return a.Value, nil
+		}}
+}
+
+// The indexer's read tools the tools ask for its candidates and modules (the manifest's invokes).
+const (
+	indexerCandidatesTool = check.IndexerModule + ".indexer_read_candidates"
+	indexerModulesTool    = check.IndexerModule + ".indexer_read_modules"
+)
+
 // runsOf says which commit the mesh runs of a module from the indexer's modules state, as the checker's own record of it does
 // (the commit the module's record was computed at); "" when the record is not readable.
 type runsOf struct{ modules check.StateRead }
@@ -371,13 +418,13 @@ func stepBound() time.Duration {
 }
 
 func main() {
-	r := check.Reader{VerdictState: read(stdio.State("verdicts")), KeptState: read(stdio.State("kept")), CandidateState: read(stdio.State("mesh-delivery-indexer.candidates")),
+	r := check.Reader{VerdictState: read(stdio.State("verdicts")), KeptState: read(stdio.State("kept")), CandidateState: ownerRead(stdio.Ask, indexerCandidatesTool),
 		PreviewState: read(stdio.State("previews")), InputState: read(stdio.State(check.InputsStateName)),
 		StepStates: map[string]check.StateRead{"mesh-build-go": read(stdio.State("mesh-build-go.steps")), "mesh-build-node": read(stdio.State("mesh-build-node.steps"))},
 		HaveState:  read(stdio.State("node-engine.have")), StepBound: stepBound(),
 		TurnState: read(stdio.State("mesh-delivery-gate.turns")), HearingState: read(stdio.State(buildrun.HearingState)),
 		AskState: read(stdio.State(check.AsksState)), BuildState: read(stdio.State("mesh-delivery-builder.builds"))}
-	r.Runs = runsOf{read(stdio.State("mesh-delivery-indexer.modules"))} // the node-engine at the commit the mesh runs, as the checker reads it
+	r.Runs = runsOf{ownerRead(stdio.Ask, indexerModulesTool)} // the node-engine at the commit the mesh runs, as the checker reads it
 	tries := stdio.State(check.TriesState)
 	source := stdio.State("mesh-delivery-gate.source")
 	trunks := func() (map[string]string, error) {

modules/mesh-delivery-checker/cmd/mesh-delivery-checker-tools/main_test.go

@@ -6,6 +6,7 @@ import (
 	"encoding/json"
 	"errors"
 	"os"
+	"regexp"
 	"slices"
 	"strings"
 	"testing"
@@ -67,6 +68,73 @@ func TestTheToolsServedAreTheFiveReadTools(t *testing.T) {
 	if _, err := RequestTools(check.StateRead{})[0].Run(map[string]any{}); err == nil {
 		t.Errorf("answered with no state to read")
 	}
+	// Issue 1966: another module's state is asked of its read tool, never read from its bus state (ADR 0596). Every
+	// stdio.State this program names of another module is one its manifest declares under reads, which the runtime grants;
+	// the indexer's candidates and modules are asked of indexer_read_candidates and indexer_read_modules, which it invokes.
+	t.Run("1966: another module's state is read only where the manifest declares it", func(t *testing.T) {
+		raw, err := os.ReadFile("../../module.json")
+		if err != nil {
+			t.Fatal(err)
+		}
+		var man struct {
+			Reads   []string `json:"reads"`
+			Invokes []string `json:"invokes"`
+		}
+		if err := json.Unmarshal(raw, &man); err != nil {
+			t.Fatal(err)
+		}
+		src, err := os.ReadFile("main.go")
+		if err != nil {
+			t.Fatal(err)
+		}
+		for _, m := range regexp.MustCompile(`stdio\.State\("([^"]+\.[^"]+)"\)`).FindAllStringSubmatch(string(src), -1) {
+			if !slices.Contains(man.Reads, m[1]) {
+				t.Errorf("main.go reads %s, which the manifest does not declare under reads: the runtime refuses it", m[1])
+			}
+		}
+		for _, tool := range []string{indexerCandidatesTool, indexerModulesTool} {
+			if !slices.Contains(man.Invokes, tool) {
+				t.Errorf("the manifest does not invoke %s", tool)
+			}
+		}
+	})
+	for _, c := range []struct {
+		name, key, answer, want string
+		failed                  bool
+	}{
+		{name: "the keys", answer: `{"owner":"mesh-delivery-indexer","state":"candidates","keys":["a","b"]}`, want: "[a b]"},
+		{name: "one key, wrapped as the tool runner hands it", key: "a",
+			answer: `{"content":[{"type":"text","text":"{\"key\":\"a\",\"found\":true,\"value\":{\"commit\":\"c\"}}"}]}`, want: `{"commit":"c"}`},
+		{name: "a key the indexer does not hold", key: "gone", answer: `{"key":"gone","found":false}`, want: ""},
+		{name: "the tool refused", key: "a", answer: `{"content":[{"type":"text","text":"refused"}],"isError":true}`, failed: true},
+	} {
+		t.Run("1966: the indexer's read tool, "+c.name, func(t *testing.T) {
+			var asked []string
+			r := ownerRead(func(key string, body any) (json.RawMessage, error) {
+				b, _ := json.Marshal(body)
+				asked = append(asked, key+" "+string(b))
+				return json.RawMessage(c.answer), nil
+			}, indexerCandidatesTool)
+			var got string
+			var err error
+			if c.key == "" {
+				var keys []string
+				keys, err = r.Keys()
+				got = strings.Trim(strings.Join([]string{"[", strings.Join(keys, " "), "]"}, ""), " ")
+			} else {
+				var raw json.RawMessage
+				raw, err = r.Get(c.key)
+				got = string(raw)
+			}
+			want := []string{indexerCandidatesTool + " {}"}
+			if c.key != "" {
+				want = []string{indexerCandidatesTool + ` {"key":"` + c.key + `"}`}
+			}
+			if (err != nil) != c.failed || (!c.failed && got != c.want) || !slices.Equal(asked, want) {
+				t.Errorf("read %q, %v, asking %v; want %q, failed %v, asking %v", got, err, asked, c.want, c.failed, want)
+			}
+		})
+	}
 	// With nothing to read from a tool says so and changes nothing.
 	for _, tl := range Tools(check.Reader{}) {
 		if tl.Name == check.StatusReadTool {