Merge pull request 'Build modules' step and toolchain lists read only the newest keys they answer, in parallel (issue 1827)' (#485) from fix/1827-bounded-reads into main

modules/mesh-build-go/cmd/mesh-build-go/read.go

@@ -7,9 +7,12 @@ package main
 import (
 	"encoding/json"
 	"fmt"
+	"log"
 	"sort"
 	"strconv"
 	"strings"
+	"sync"
+	"time"
 
 	stdio "git.novox.be/novox/mesh-sdk/go"
 	"git.novox.be/novox/mesh-sdk/go/delivery"
@@ -39,6 +42,53 @@ func readOf(s stdio.KeptState) StateRead {
 	}}
 }
 
+// MaxStateReads is the most values one read tool reads from a state in a call, and stateReadParallel how many of them
+// are in flight at once. Every value is a round trip from the tool through the runtime to the bus, so a call that read
+// every key of a large state one after the other outlasted the call's 30 s (issue 1827: 1164 keys, 20 MB).
+const (
+	MaxStateReads     = 1000
+	stateReadParallel = 16
+)
+
+// readValues reads the values of keys, stateReadParallel at a time, in the order of keys (nil for a key with none). It
+// stops starting reads after the first error and returns it.
+func readValues(keys []string, get func(string) (json.RawMessage, error)) ([]json.RawMessage, error) {
+	out := make([]json.RawMessage, len(keys))
+	var (
+		wg   sync.WaitGroup
+		mu   sync.Mutex
+		fail error
+		next = make(chan int)
+	)
+	for w := 0; w < stateReadParallel && w < len(keys); w++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			for i := range next {
+				raw, err := get(keys[i])
+				mu.Lock()
+				if err != nil && fail == nil {
+					fail = err
+				}
+				mu.Unlock()
+				out[i] = raw
+			}
+		}()
+	}
+	for i := range keys {
+		mu.Lock()
+		stop := fail != nil
+		mu.Unlock()
+		if stop {
+			break
+		}
+		next <- i
+	}
+	close(next)
+	wg.Wait()
+	return out, fail
+}
+
 // stepKey is the key of a step of this node: the id alone, or the whole key <node>.<id> as a step tool answered it.
 func (m *Module) stepKey(id string) (string, error) {
 	id = strings.TrimSpace(id)
@@ -80,27 +130,41 @@ type StepLine struct {
 	Reason  string `json:"reason,omitempty"`
 }
 
-// RecentSteps are this node's steps, the latest started first, at most limit (ten when limit is not above zero).
-func (m *Module) RecentSteps(limit int) ([]StepLine, error) {
+// RecentSteps are this node's steps, the latest started first, at most limit (ten when limit is not above zero). Only
+// the node's own keys (<node>.) are listed and the newest max(limit*4, 100) of them read (at most MaxStateReads): a step's
+// id is base-36 milliseconds and random digits, so its string order is its start order. cut says older steps were not
+// read. The values still order the lines, since an ask step's id carries the ask time.
+func (m *Module) RecentSteps(limit int) (lines []StepLine, cut bool, err error) {
 	if limit <= 0 {
 		limit = 10
 	}
 	if m.ReadSteps.Keys == nil || m.ReadSteps.Get == nil {
-		return nil, fmt.Errorf("the steps state cannot be read here")
+		return nil, false, fmt.Errorf("the steps state cannot be read here")
 	}
+	start := time.Now()
 	keys, err := m.ReadSteps.Keys()
 	if err != nil {
-		return nil, err
+		return nil, false, err
+	}
+	own := keys[:0:0]
+	for _, k := range keys {
+		if strings.HasPrefix(k, m.Node+".") {
+			if node, _, err := delivery.ParseStepKey(k); err == nil && node == m.Node {
+				own = append(own, k)
+			}
+		}
+	}
+	sort.Sort(sort.Reverse(sort.StringSlice(own)))
+	if n := min(max(limit*4, 100), MaxStateReads); len(own) > n {
+		own, cut = own[:n], true
+	}
+	raws, err := readValues(own, m.ReadSteps.Get)
+	log.Printf("steps read: %d of %d keys listed read in %v (cut %v)", len(own), len(keys), time.Since(start).Round(time.Millisecond), cut)
+	if err != nil {
+		return nil, cut, err
 	}
 	var steps []delivery.Step
-	for _, k := range keys {
-		if node, _, err := delivery.ParseStepKey(k); err != nil || node != m.Node {
-			continue
-		}
-		raw, err := m.ReadSteps.Get(k)
-		if err != nil {
-			return nil, err
-		}
+	for _, raw := range raws {
 		if len(raw) == 0 {
 			continue
 		}
@@ -122,7 +186,7 @@ func (m *Module) RecentSteps(limit int) ([]StepLine, error) {
 		}
 		out = append(out, l)
 	}
-	return out, nil
+	return out, cut, nil
 }
 
 // ReadToolchains is every key of the toolchains state (<node>.<language>) with its stored value.
@@ -130,24 +194,30 @@ func (m *Module) ReadToolchains() (map[string]delivery.Toolchain, error) {
 	if m.ReadToolchainsState.Keys == nil || m.ReadToolchainsState.Get == nil {
 		return nil, fmt.Errorf("the toolchains state cannot be read here")
 	}
+	start := time.Now()
 	keys, err := m.ReadToolchainsState.Keys()
 	if err != nil {
 		return nil, err
 	}
+	cut := len(keys) > MaxStateReads
+	if cut {
+		keys = keys[:MaxStateReads] // a node has a key per language: far fewer in practice
+	}
+	raws, err := readValues(keys, m.ReadToolchainsState.Get)
+	log.Printf("toolchains read: %d keys read in %v (cut %v: keys past %d were not read)", len(keys), time.Since(start).Round(time.Millisecond), cut, MaxStateReads)
+	if err != nil {
+		return nil, err
+	}
 	out := map[string]delivery.Toolchain{}
-	for _, k := range keys {
-		raw, err := m.ReadToolchainsState.Get(k)
-		if err != nil {
-			return nil, err
-		}
+	for i, raw := range raws {
 		if len(raw) == 0 {
 			continue
 		}
 		t, err := delivery.DecodeToolchain(raw)
 		if err != nil {
-			return nil, fmt.Errorf("%s: %w", k, err)
+			return nil, fmt.Errorf("%s: %w", keys[i], err)
 		}
-		out[k] = t
+		out[keys[i]] = t
 	}
 	return out, nil
 }
@@ -171,8 +241,13 @@ func (m *Module) ReadTools() []stdio.Tool {
 			Input: map[string]any{"type": "object", "properties": map[string]any{
 				"limit": map[string]any{"type": "integer", "description": "how many, at most; 10 when left out"}}},
 			Run: func(args map[string]any) (any, error) {
-				steps, err := m.RecentSteps(intArg(args["limit"]))
-				return map[string]any{"node": m.Node, "steps": steps}, err
+				steps, cut, err := m.RecentSteps(intArg(args["limit"]))
+				ans := map[string]any{"node": m.Node, "steps": steps}
+				if cut {
+					ans["cut"] = true
+					ans["note"] = fmt.Sprintf("this node has more steps stored than one call reads; older steps were not read (ask for a larger limit, at most %d reads)", MaxStateReads)
+				}
+				return ans, err
 			}},
 		{Name: ToolchainsReadTool,
 			Description: "What the module's toolchains state holds: each key <node>.<language> with the version installed, the " +

modules/mesh-build-go/cmd/mesh-build-go/read_test.go

@@ -3,8 +3,10 @@ package main
 import (
 	"context"
 	"encoding/json"
+	"fmt"
 	"slices"
 	"strings"
+	"sync/atomic"
 	"testing"
 	"time"
 
@@ -145,3 +147,62 @@ func TestReadToolsAreInTheManifestAndNeedNoToolchain(t *testing.T) {
 		t.Errorf("the read refused: %v", err)
 	}
 }
+
+// 1827: on the live shape (4 nodes, 600 steps each; a steps state of 1164 keys / 20 MB timed out at 30 s) the steps tool
+// lists, then reads only this node's keys, in parallel, at most MaxStateReads of them, and says when it cut.
+func TestRecentStepsReadsOnlyTheNodesKeysInParallelAndBounded(t *testing.T) {
+	t0 := time.Date(2026, 10, 25, 9, 0, 0, 0, time.UTC)
+	for _, row := range []struct {
+		perNode, limit int
+		reads          int64
+		steps          int
+		cut            bool
+	}{
+		{20, 0, 20, 10, false},
+		{600, 0, 100, 10, true},
+		{1500, 300, MaxStateReads, 300, true},
+	} {
+		var reads, inFlight, maxFlight atomic.Int64
+		stored := map[string][]byte{}
+		for _, n := range []string{"ace", "g14", "novox", "shanks"} {
+			for i := 0; i < row.perNode; i++ {
+				b, _ := delivery.EncodeStep(delivery.Step{ID: fmt.Sprintf("s%04d", i), Tool: "t", Node: n, State: delivery.StepPassed, Started: t0.Add(time.Duration(i) * time.Second)})
+				stored[n+".s"+fmt.Sprintf("%04d", i)] = b
+			}
+		}
+		m := &Module{Node: "shanks"}
+		m.ReadSteps = StateRead{
+			Keys: func() ([]string, error) {
+				var k []string
+				for key := range stored {
+					k = append(k, key)
+				}
+				return k, nil
+			},
+			Get: func(key string) (json.RawMessage, error) {
+				reads.Add(1)
+				now := inFlight.Add(1)
+				for o := maxFlight.Load(); now > o && !maxFlight.CompareAndSwap(o, now); o = maxFlight.Load() {
+				}
+				time.Sleep(time.Millisecond)
+				inFlight.Add(-1)
+				if !strings.HasPrefix(key, "shanks.") {
+					t.Errorf("read %s, a key of another node", key)
+				}
+				return stored[key], nil
+			},
+		}
+		start := time.Now()
+		lines, cut, err := m.RecentSteps(row.limit)
+		if err != nil || len(lines) != row.steps || cut != row.cut || reads.Load() != row.reads {
+			t.Errorf("%d a node: %d steps, cut %v, %d reads, err %v; want %d, %v, %d", row.perNode, len(lines), cut, reads.Load(), err, row.steps, row.cut, row.reads)
+		}
+		if row.cut && len(lines) > 0 && lines[0].ID != fmt.Sprintf("s%04d", row.perNode-1) {
+			t.Errorf("%d a node: newest answered %s", row.perNode, lines[0].ID)
+		}
+		if maxFlight.Load() < 2 {
+			t.Errorf("%d a node: values read one at a time", row.perNode)
+		}
+		t.Logf("%d a node: %d reads in %v (one after the other: %v)", row.perNode, reads.Load(), time.Since(start), time.Duration(reads.Load())*time.Millisecond)
+	}
+}

modules/mesh-build-image/cmd/mesh-build-image/read.go

@@ -7,9 +7,12 @@ package main
 import (
 	"encoding/json"
 	"fmt"
+	"log"
 	"sort"
 	"strconv"
 	"strings"
+	"sync"
+	"time"
 
 	stdio "git.novox.be/novox/mesh-sdk/go"
 	"git.novox.be/novox/mesh-sdk/go/delivery"
@@ -38,6 +41,53 @@ func readOf(s stdio.KeptState) StateRead {
 	}}
 }
 
+// MaxStateReads is the most values one read tool reads from a state in a call, and stateReadParallel how many of them
+// are in flight at once. Every value is a round trip from the tool through the runtime to the bus, so a call that read
+// every key of a large state one after the other outlasted the call's 30 s (issue 1827: 1164 keys, 20 MB).
+const (
+	MaxStateReads     = 1000
+	stateReadParallel = 16
+)
+
+// readValues reads the values of keys, stateReadParallel at a time, in the order of keys (nil for a key with none). It
+// stops starting reads after the first error and returns it.
+func readValues(keys []string, get func(string) (json.RawMessage, error)) ([]json.RawMessage, error) {
+	out := make([]json.RawMessage, len(keys))
+	var (
+		wg   sync.WaitGroup
+		mu   sync.Mutex
+		fail error
+		next = make(chan int)
+	)
+	for w := 0; w < stateReadParallel && w < len(keys); w++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			for i := range next {
+				raw, err := get(keys[i])
+				mu.Lock()
+				if err != nil && fail == nil {
+					fail = err
+				}
+				mu.Unlock()
+				out[i] = raw
+			}
+		}()
+	}
+	for i := range keys {
+		mu.Lock()
+		stop := fail != nil
+		mu.Unlock()
+		if stop {
+			break
+		}
+		next <- i
+	}
+	close(next)
+	wg.Wait()
+	return out, fail
+}
+
 // stepKey is the key of a step of this node: the id alone, or the whole key <node>.<id> as a step tool answered it.
 func (m *Module) stepKey(id string) (string, error) {
 	id = strings.TrimSpace(id)
@@ -79,27 +129,41 @@ type StepLine struct {
 	Reason  string `json:"reason,omitempty"`
 }
 
-// RecentSteps are this node's steps, the latest started first, at most limit (ten when limit is not above zero).
-func (m *Module) RecentSteps(limit int) ([]StepLine, error) {
+// RecentSteps are this node's steps, the latest started first, at most limit (ten when limit is not above zero). Only
+// the node's own keys (<node>.) are listed and the newest max(limit*4, 100) of them read (at most MaxStateReads): a step's
+// id is base-36 milliseconds and random digits, so its string order is its start order. cut says older steps were not
+// read. The values still order the lines, since an ask step's id carries the ask time.
+func (m *Module) RecentSteps(limit int) (lines []StepLine, cut bool, err error) {
 	if limit <= 0 {
 		limit = 10
 	}
 	if m.ReadSteps.Keys == nil || m.ReadSteps.Get == nil {
-		return nil, fmt.Errorf("the steps state cannot be read here")
+		return nil, false, fmt.Errorf("the steps state cannot be read here")
 	}
+	start := time.Now()
 	keys, err := m.ReadSteps.Keys()
 	if err != nil {
-		return nil, err
+		return nil, false, err
+	}
+	own := keys[:0:0]
+	for _, k := range keys {
+		if strings.HasPrefix(k, m.Node+".") {
+			if node, _, err := delivery.ParseStepKey(k); err == nil && node == m.Node {
+				own = append(own, k)
+			}
+		}
+	}
+	sort.Sort(sort.Reverse(sort.StringSlice(own)))
+	if n := min(max(limit*4, 100), MaxStateReads); len(own) > n {
+		own, cut = own[:n], true
+	}
+	raws, err := readValues(own, m.ReadSteps.Get)
+	log.Printf("steps read: %d of %d keys listed read in %v (cut %v)", len(own), len(keys), time.Since(start).Round(time.Millisecond), cut)
+	if err != nil {
+		return nil, cut, err
 	}
 	var steps []delivery.Step
-	for _, k := range keys {
-		if node, _, err := delivery.ParseStepKey(k); err != nil || node != m.Node {
-			continue
-		}
-		raw, err := m.ReadSteps.Get(k)
-		if err != nil {
-			return nil, err
-		}
+	for _, raw := range raws {
 		if len(raw) == 0 {
 			continue
 		}
@@ -121,7 +185,7 @@ func (m *Module) RecentSteps(limit int) ([]StepLine, error) {
 		}
 		out = append(out, l)
 	}
-	return out, nil
+	return out, cut, nil
 }
 
 // ReadTools are the module's read tools. All are read-only.
@@ -143,8 +207,13 @@ func (m *Module) ReadTools() []stdio.Tool {
 			Input: map[string]any{"type": "object", "properties": map[string]any{
 				"limit": map[string]any{"type": "integer", "description": "how many, at most; 10 when left out"}}},
 			Run: func(args map[string]any) (any, error) {
-				steps, err := m.RecentSteps(intArg(args["limit"]))
-				return map[string]any{"node": m.Node, "steps": steps}, err
+				steps, cut, err := m.RecentSteps(intArg(args["limit"]))
+				ans := map[string]any{"node": m.Node, "steps": steps}
+				if cut {
+					ans["cut"] = true
+					ans["note"] = fmt.Sprintf("this node has more steps stored than one call reads; older steps were not read (ask for a larger limit, at most %d reads)", MaxStateReads)
+				}
+				return ans, err
 			}},
 	}
 }

modules/mesh-build-image/cmd/mesh-build-image/read_test.go

@@ -2,7 +2,11 @@ package main
 
 import (
 	"encoding/json"
+	"fmt"
+	"strings"
+	"sync/atomic"
 	"testing"
+	"time"
 
 	"git.novox.be/novox/mesh-sdk/go/delivery"
 )
@@ -39,8 +43,67 @@ func TestTheReadToolsAnswerAStepsResult(t *testing.T) {
 	if err := json.Unmarshal(got.Result, &back); err != nil || back.Digest != res.Digest {
 		t.Errorf("result = %s, %v", got.Result, err)
 	}
-	lines, err := m.RecentSteps(0)
+	lines, _, err := m.RecentSteps(0)
 	if err != nil || len(lines) != 1 || lines[0].Tool != BuildTool {
 		t.Errorf("steps = %+v, %v", lines, err)
 	}
 }
+
+// 1827: on the live shape (4 nodes, 600 steps each; a steps state of 1164 keys / 20 MB timed out at 30 s) the steps tool
+// lists, then reads only this node's keys, in parallel, at most MaxStateReads of them, and says when it cut.
+func TestRecentStepsReadsOnlyTheNodesKeysInParallelAndBounded(t *testing.T) {
+	t0 := time.Date(2026, 10, 25, 9, 0, 0, 0, time.UTC)
+	for _, row := range []struct {
+		perNode, limit int
+		reads          int64
+		steps          int
+		cut            bool
+	}{
+		{20, 0, 20, 10, false},
+		{600, 0, 100, 10, true},
+		{1500, 300, MaxStateReads, 300, true},
+	} {
+		var reads, inFlight, maxFlight atomic.Int64
+		stored := map[string][]byte{}
+		for _, n := range []string{"ace", "g14", "novox", "shanks"} {
+			for i := 0; i < row.perNode; i++ {
+				b, _ := delivery.EncodeStep(delivery.Step{ID: fmt.Sprintf("s%04d", i), Tool: "t", Node: n, State: delivery.StepPassed, Started: t0.Add(time.Duration(i) * time.Second)})
+				stored[n+".s"+fmt.Sprintf("%04d", i)] = b
+			}
+		}
+		m := &Module{Node: "shanks"}
+		m.ReadSteps = StateRead{
+			Keys: func() ([]string, error) {
+				var k []string
+				for key := range stored {
+					k = append(k, key)
+				}
+				return k, nil
+			},
+			Get: func(key string) (json.RawMessage, error) {
+				reads.Add(1)
+				now := inFlight.Add(1)
+				for o := maxFlight.Load(); now > o && !maxFlight.CompareAndSwap(o, now); o = maxFlight.Load() {
+				}
+				time.Sleep(time.Millisecond)
+				inFlight.Add(-1)
+				if !strings.HasPrefix(key, "shanks.") {
+					t.Errorf("read %s, a key of another node", key)
+				}
+				return stored[key], nil
+			},
+		}
+		start := time.Now()
+		lines, cut, err := m.RecentSteps(row.limit)
+		if err != nil || len(lines) != row.steps || cut != row.cut || reads.Load() != row.reads {
+			t.Errorf("%d a node: %d steps, cut %v, %d reads, err %v; want %d, %v, %d", row.perNode, len(lines), cut, reads.Load(), err, row.steps, row.cut, row.reads)
+		}
+		if row.cut && len(lines) > 0 && lines[0].ID != fmt.Sprintf("s%04d", row.perNode-1) {
+			t.Errorf("%d a node: newest answered %s", row.perNode, lines[0].ID)
+		}
+		if maxFlight.Load() < 2 {
+			t.Errorf("%d a node: values read one at a time", row.perNode)
+		}
+		t.Logf("%d a node: %d reads in %v (one after the other: %v)", row.perNode, reads.Load(), time.Since(start), time.Duration(reads.Load())*time.Millisecond)
+	}
+}

modules/mesh-build-node/cmd/mesh-build-node/read.go

@@ -7,9 +7,12 @@ package main
 import (
 	"encoding/json"
 	"fmt"
+	"log"
 	"sort"
 	"strconv"
 	"strings"
+	"sync"
+	"time"
 
 	stdio "git.novox.be/novox/mesh-sdk/go"
 	"git.novox.be/novox/mesh-sdk/go/delivery"
@@ -39,6 +42,53 @@ func readOf(s stdio.KeptState) StateRead {
 	}}
 }
 
+// MaxStateReads is the most values one read tool reads from a state in a call, and stateReadParallel how many of them
+// are in flight at once. Every value is a round trip from the tool through the runtime to the bus, so a call that read
+// every key of a large state one after the other outlasted the call's 30 s (issue 1827: 1164 keys, 20 MB).
+const (
+	MaxStateReads     = 1000
+	stateReadParallel = 16
+)
+
+// readValues reads the values of keys, stateReadParallel at a time, in the order of keys (nil for a key with none). It
+// stops starting reads after the first error and returns it.
+func readValues(keys []string, get func(string) (json.RawMessage, error)) ([]json.RawMessage, error) {
+	out := make([]json.RawMessage, len(keys))
+	var (
+		wg   sync.WaitGroup
+		mu   sync.Mutex
+		fail error
+		next = make(chan int)
+	)
+	for w := 0; w < stateReadParallel && w < len(keys); w++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			for i := range next {
+				raw, err := get(keys[i])
+				mu.Lock()
+				if err != nil && fail == nil {
+					fail = err
+				}
+				mu.Unlock()
+				out[i] = raw
+			}
+		}()
+	}
+	for i := range keys {
+		mu.Lock()
+		stop := fail != nil
+		mu.Unlock()
+		if stop {
+			break
+		}
+		next <- i
+	}
+	close(next)
+	wg.Wait()
+	return out, fail
+}
+
 // stepKey is the key of a step of this node: the id alone, or the whole key <node>.<id> as a step tool answered it.
 func (m *Module) stepKey(id string) (string, error) {
 	id = strings.TrimSpace(id)
@@ -80,27 +130,41 @@ type StepLine struct {
 	Reason  string `json:"reason,omitempty"`
 }
 
-// RecentSteps are this node's steps, the latest started first, at most limit (ten when limit is not above zero).
-func (m *Module) RecentSteps(limit int) ([]StepLine, error) {
+// RecentSteps are this node's steps, the latest started first, at most limit (ten when limit is not above zero). Only
+// the node's own keys (<node>.) are listed and the newest max(limit*4, 100) of them read (at most MaxStateReads): a step's
+// id is base-36 milliseconds and random digits, so its string order is its start order. cut says older steps were not
+// read. The values still order the lines, since an ask step's id carries the ask time.
+func (m *Module) RecentSteps(limit int) (lines []StepLine, cut bool, err error) {
 	if limit <= 0 {
 		limit = 10
 	}
 	if m.ReadSteps.Keys == nil || m.ReadSteps.Get == nil {
-		return nil, fmt.Errorf("the steps state cannot be read here")
+		return nil, false, fmt.Errorf("the steps state cannot be read here")
 	}
+	start := time.Now()
 	keys, err := m.ReadSteps.Keys()
 	if err != nil {
-		return nil, err
+		return nil, false, err
+	}
+	own := keys[:0:0]
+	for _, k := range keys {
+		if strings.HasPrefix(k, m.Node+".") {
+			if node, _, err := delivery.ParseStepKey(k); err == nil && node == m.Node {
+				own = append(own, k)
+			}
+		}
+	}
+	sort.Sort(sort.Reverse(sort.StringSlice(own)))
+	if n := min(max(limit*4, 100), MaxStateReads); len(own) > n {
+		own, cut = own[:n], true
+	}
+	raws, err := readValues(own, m.ReadSteps.Get)
+	log.Printf("steps read: %d of %d keys listed read in %v (cut %v)", len(own), len(keys), time.Since(start).Round(time.Millisecond), cut)
+	if err != nil {
+		return nil, cut, err
 	}
 	var steps []delivery.Step
-	for _, k := range keys {
-		if node, _, err := delivery.ParseStepKey(k); err != nil || node != m.Node {
-			continue
-		}
-		raw, err := m.ReadSteps.Get(k)
-		if err != nil {
-			return nil, err
-		}
+	for _, raw := range raws {
 		if len(raw) == 0 {
 			continue
 		}
@@ -122,7 +186,7 @@ func (m *Module) RecentSteps(limit int) ([]StepLine, error) {
 		}
 		out = append(out, l)
 	}
-	return out, nil
+	return out, cut, nil
 }
 
 // ReadToolchains is every key of the toolchains state (<node>.<language>) with its stored value.
@@ -130,24 +194,30 @@ func (m *Module) ReadToolchains() (map[string]delivery.Toolchain, error) {
 	if m.ReadToolchainsState.Keys == nil || m.ReadToolchainsState.Get == nil {
 		return nil, fmt.Errorf("the toolchains state cannot be read here")
 	}
+	start := time.Now()
 	keys, err := m.ReadToolchainsState.Keys()
 	if err != nil {
 		return nil, err
 	}
+	cut := len(keys) > MaxStateReads
+	if cut {
+		keys = keys[:MaxStateReads] // a node has a key per language: far fewer in practice
+	}
+	raws, err := readValues(keys, m.ReadToolchainsState.Get)
+	log.Printf("toolchains read: %d keys read in %v (cut %v: keys past %d were not read)", len(keys), time.Since(start).Round(time.Millisecond), cut, MaxStateReads)
+	if err != nil {
+		return nil, err
+	}
 	out := map[string]delivery.Toolchain{}
-	for _, k := range keys {
-		raw, err := m.ReadToolchainsState.Get(k)
-		if err != nil {
-			return nil, err
-		}
+	for i, raw := range raws {
 		if len(raw) == 0 {
 			continue
 		}
 		t, err := delivery.DecodeToolchain(raw)
 		if err != nil {
-			return nil, fmt.Errorf("%s: %w", k, err)
+			return nil, fmt.Errorf("%s: %w", keys[i], err)
 		}
-		out[k] = t
+		out[keys[i]] = t
 	}
 	return out, nil
 }
@@ -171,8 +241,13 @@ func (m *Module) ReadTools() []stdio.Tool {
 			Input: map[string]any{"type": "object", "properties": map[string]any{
 				"limit": map[string]any{"type": "integer", "description": "how many, at most; 10 when left out"}}},
 			Run: func(args map[string]any) (any, error) {
-				steps, err := m.RecentSteps(intArg(args["limit"]))
-				return map[string]any{"node": m.Node, "steps": steps}, err
+				steps, cut, err := m.RecentSteps(intArg(args["limit"]))
+				ans := map[string]any{"node": m.Node, "steps": steps}
+				if cut {
+					ans["cut"] = true
+					ans["note"] = fmt.Sprintf("this node has more steps stored than one call reads; older steps were not read (ask for a larger limit, at most %d reads)", MaxStateReads)
+				}
+				return ans, err
 			}},
 		{Name: ToolchainsReadTool,
 			Description: "What the module's toolchains state holds: each key <node>.<language> with the version installed, the " +

modules/mesh-build-node/cmd/mesh-build-node/read_test.go

@@ -3,8 +3,10 @@ package main
 import (
 	"context"
 	"encoding/json"
+	"fmt"
 	"slices"
 	"strings"
+	"sync/atomic"
 	"testing"
 	"time"
 
@@ -145,3 +147,62 @@ func TestReadToolsAreInTheManifestAndNeedNoToolchain(t *testing.T) {
 		t.Errorf("the read refused: %v", err)
 	}
 }
+
+// 1827: on the live shape (4 nodes, 600 steps each; a steps state of 1164 keys / 20 MB timed out at 30 s) the steps tool
+// lists, then reads only this node's keys, in parallel, at most MaxStateReads of them, and says when it cut.
+func TestRecentStepsReadsOnlyTheNodesKeysInParallelAndBounded(t *testing.T) {
+	t0 := time.Date(2026, 10, 25, 9, 0, 0, 0, time.UTC)
+	for _, row := range []struct {
+		perNode, limit int
+		reads          int64
+		steps          int
+		cut            bool
+	}{
+		{20, 0, 20, 10, false},
+		{600, 0, 100, 10, true},
+		{1500, 300, MaxStateReads, 300, true},
+	} {
+		var reads, inFlight, maxFlight atomic.Int64
+		stored := map[string][]byte{}
+		for _, n := range []string{"ace", "g14", "novox", "shanks"} {
+			for i := 0; i < row.perNode; i++ {
+				b, _ := delivery.EncodeStep(delivery.Step{ID: fmt.Sprintf("s%04d", i), Tool: "t", Node: n, State: delivery.StepPassed, Started: t0.Add(time.Duration(i) * time.Second)})
+				stored[n+".s"+fmt.Sprintf("%04d", i)] = b
+			}
+		}
+		m := &Module{Node: "shanks"}
+		m.ReadSteps = StateRead{
+			Keys: func() ([]string, error) {
+				var k []string
+				for key := range stored {
+					k = append(k, key)
+				}
+				return k, nil
+			},
+			Get: func(key string) (json.RawMessage, error) {
+				reads.Add(1)
+				now := inFlight.Add(1)
+				for o := maxFlight.Load(); now > o && !maxFlight.CompareAndSwap(o, now); o = maxFlight.Load() {
+				}
+				time.Sleep(time.Millisecond)
+				inFlight.Add(-1)
+				if !strings.HasPrefix(key, "shanks.") {
+					t.Errorf("read %s, a key of another node", key)
+				}
+				return stored[key], nil
+			},
+		}
+		start := time.Now()
+		lines, cut, err := m.RecentSteps(row.limit)
+		if err != nil || len(lines) != row.steps || cut != row.cut || reads.Load() != row.reads {
+			t.Errorf("%d a node: %d steps, cut %v, %d reads, err %v; want %d, %v, %d", row.perNode, len(lines), cut, reads.Load(), err, row.steps, row.cut, row.reads)
+		}
+		if row.cut && len(lines) > 0 && lines[0].ID != fmt.Sprintf("s%04d", row.perNode-1) {
+			t.Errorf("%d a node: newest answered %s", row.perNode, lines[0].ID)
+		}
+		if maxFlight.Load() < 2 {
+			t.Errorf("%d a node: values read one at a time", row.perNode)
+		}
+		t.Logf("%d a node: %d reads in %v (one after the other: %v)", row.perNode, reads.Load(), time.Since(start), time.Duration(reads.Load())*time.Millisecond)
+	}
+}