Read only the node's own steps, in parallel and bounded, so build_*_steps answers within the call's 30 s (issue 1827)

On a steps state of 1164 keys / 20 MB (mesh-build-node: 10034 keys) the read tools listed every key and
then read each value one round trip at a time, filtering by node only after the Get, so they timed out
at 30 s. Now the keys are filtered by the node's prefix before any Get, the values are read 16 at a
time, at most 1000 a call (the answer says it was cut), and one log line gives rows read and time.
build_*_toolchains reads its values the same parallel way. The kind: a read tool that reads a whole
state key by key; every read tool of the three modules is covered.

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 +130,39 @@ 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 read, at most MaxStateReads of them; cut says more were stored than were read, so
+// the newest may be missing. A step's id says nothing of when it started, so the values are what orders them.
+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)
+			}
+		}
+	}
+	if len(own) > MaxStateReads {
+		own, cut = own[:MaxStateReads], 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 +184,7 @@ 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 +192,29 @@ 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
 	}
+	if len(keys) > MaxStateReads {
+		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", len(keys), time.Since(start).Round(time.Millisecond))
+	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 +238,13 @@ 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 than %d steps stored; %d were read, so the newest may be missing", MaxStateReads, 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 +147,59 @@ 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 int
+		reads   int64
+		steps   int
+		cut     bool
+	}{
+		{20, 20, 10, false},
+		{600, 600, 10, false},
+		{1500, MaxStateReads, 10, 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(0)
+		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 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 +129,39 @@ 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 read, at most MaxStateReads of them; cut says more were stored than were read, so
+// the newest may be missing. A step's id says nothing of when it started, so the values are what orders them.
+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)
+			}
+		}
+	}
+	if len(own) > MaxStateReads {
+		own, cut = own[:MaxStateReads], 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 +183,7 @@ 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 +205,13 @@ 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 than %d steps stored; %d were read, so the newest may be missing", MaxStateReads, 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 +43,64 @@ 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 int
+		reads   int64
+		steps   int
+		cut     bool
+	}{
+		{20, 20, 10, false},
+		{600, 600, 10, false},
+		{1500, MaxStateReads, 10, 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(0)
+		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 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 +130,39 @@ 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 read, at most MaxStateReads of them; cut says more were stored than were read, so
+// the newest may be missing. A step's id says nothing of when it started, so the values are what orders them.
+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)
+			}
+		}
+	}
+	if len(own) > MaxStateReads {
+		own, cut = own[:MaxStateReads], 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 +184,7 @@ 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 +192,29 @@ 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
 	}
+	if len(keys) > MaxStateReads {
+		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", len(keys), time.Since(start).Round(time.Millisecond))
+	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 +238,13 @@ 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 than %d steps stored; %d were read, so the newest may be missing", MaxStateReads, 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 +147,59 @@ 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 int
+		reads   int64
+		steps   int
+		cut     bool
+	}{
+		{20, 20, 10, false},
+		{600, 600, 10, false},
+		{1500, MaxStateReads, 10, 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(0)
+		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 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)
+	}
+}