modules/nats/cmd/nats-tools/keep_test.go

@@ -4,8 +4,11 @@ import (
 	"fmt"
 	"strings"
 	"testing"
+	"time"
 
 	"git.novox.be/novox/mesh-sdk/go/catalogue"
+
+	"nats-tools/internal/keeper"
 )
 
 // The keeper's inputs (design 25 § 12.2; CAT-N2): a manifest-accepted read with the indexer's revision when it carries
@@ -63,3 +66,30 @@ func line(module, digest string, revision uint64, entries []catalogue.BusStateEn
 	}
 	return fmt.Sprintf("%s %s %d [%s]", module, digest, revision, strings.Join(es, " "))
 }
+
+// The keeper's health tool (CAT-N6): healthy naming its pass; unhealthy, naming why, when its pass is old or verdicts
+// wait on its consumer `<node>_nats_keeper` past the bound.
+func TestTheKeepersHealthToolReadsItsStatusAndItsConsumer(t *testing.T) {
+	at := time.Date(2026, 11, 4, 12, 0, 0, 0, time.UTC)
+	jsz := `{"account_details":[{"stream_detail":[{"name":"EVENTS","consumer_detail":[{"name":"anchor_nats_keeper","num_pending":3},{"name":"anchor_nats","num_pending":9}]}]}]}`
+	status := keeper.Status{Started: at.Add(-time.Hour), Pass: at.Add(-time.Minute), Heard: at.Add(-time.Minute),
+		FirstView: keeper.FirstViewStatus{Owner: keeper.FirstViewOwner, Verb: keeper.FirstViewVerb, Answered: at.Add(-time.Hour)}}
+	none := func() (map[string]keeper.Asked, error) { return nil, nil }
+	for _, row := range []struct {
+		name  string
+		now   time.Time
+		state string
+		why   string
+	}{
+		{"its pass is fresh", at, "healthy", "last pass 2026-11-04T11:59:00Z"},
+		{"its pass and its verdicts are old", at.Add(5 * time.Minute), "unhealthy", "3 accepted verdict(s) wait on its consumer"},
+	} {
+		t.Run(row.name, func(t *testing.T) {
+			a := keeperHealth(func() (keeper.Status, error) { return status, nil }, none,
+				func() ([]byte, error) { return []byte(jsz), nil }, func() time.Time { return row.now })
+			if a.State != row.state || !strings.Contains(a.Why, row.why) {
+				t.Errorf("answered %+v: %s, naming %q", a, row.state, row.why)
+			}
+		})
+	}
+}

modules/nats/cmd/nats-tools/keeper_health.go

@@ -0,0 +1,89 @@
+package main
+
+import (
+	"encoding/json"
+	"strings"
+	"time"
+
+	stdio "git.novox.be/novox/mesh-sdk/go"
+	"git.novox.be/novox/mesh-sdk/go/health"
+
+	"nats-tools/internal/keeper"
+)
+
+// The keeper's health, as the node-engine asks it of the process keeper (design 25 § 12.2-12.3; CAT-N6): its status
+// from its own state asked, what it holds, and how many accepted verdicts wait on its consumer, read from the bus's
+// monitoring endpoint.
+
+// StatusInState reads the keeper's status through the runtime.
+func StatusInState() (keeper.Status, error) {
+	e, err := stdio.State(keeper.StateAsked).Get(keeper.KeyStatus)
+	if err != nil || e == nil {
+		return keeper.Status{}, err
+	}
+	var s keeper.Status
+	return s, json.Unmarshal(e.Value, &s)
+}
+
+// keeperPending is how many messages wait on the keeper's consumer on EVENTS (`<node>_nats_keeper`), or -1 unread.
+func keeperPending(jsz []byte) int {
+	var doc struct {
+		Accounts []struct {
+			Streams []struct {
+				Name      string `json:"name"`
+				Consumers []struct {
+					Name    string `json:"name"`
+					Pending int    `json:"num_pending"`
+				} `json:"consumer_detail"`
+			} `json:"stream_detail"`
+		} `json:"account_details"`
+	}
+	if json.Unmarshal(jsz, &doc) != nil {
+		return -1
+	}
+	for _, a := range doc.Accounts {
+		for _, s := range a.Streams {
+			for _, c := range s.Consumers {
+				if s.Name == "EVENTS" && strings.HasSuffix(c.Name, "_"+keeper.Module+"_keeper") {
+					return c.Pending
+				}
+			}
+		}
+	}
+	return -1
+}
+
+// keeperHealth is the tool's answer.
+func keeperHealth(status func() (keeper.Status, error), read heldEntries, jsz func() ([]byte, error), now func() time.Time) health.Answer {
+	s, err := status()
+	if err != nil {
+		return health.Unhealthy("The keeper's status cannot be read from its own state: " + err.Error())
+	}
+	held, _ := read()
+	pending := -1
+	if doc, err := jsz(); err == nil {
+		pending = keeperPending(doc)
+	}
+	h := keeper.HealthOf(s, held, pending, now())
+	why := h.Why + "; last pass " + h.Pass
+	for _, l := range []struct {
+		name  string
+		lines []string
+	}{{"refused", h.Refused}, {"waiting", h.Waiting}, {"past the raise mark", h.Full}} {
+		if len(l.lines) > 0 {
+			why += "; " + l.name + ": " + strings.Join(l.lines, ", ")
+		}
+	}
+	if !h.Healthy {
+		return health.Unhealthy("The keeper is unhealthy: " + why + ".")
+	}
+	return health.Healthy("The keeper is healthy: " + why + ".")
+}
+
+func keeperHealthTool(status func() (keeper.Status, error), read heldEntries, jsz func() ([]byte, error)) stdio.Tool {
+	return stdio.Tool{Name: "nats_keeper_health",
+		Description: "The bus module's keeper's health, as the node-engine asks it: unhealthy, naming why, when its fill pass is more than three minutes old, its first view (the indexer's indexer_bus_state) has not answered, or accepted verdicts wait on its consumer unanswered past three minutes; it names beside the entries it could not create, the ones waiting, and those past the raise mark (another module's full entry raises that module's condition and leaves the keeper healthy).",
+		Run: func(map[string]any) (any, error) {
+			return keeperHealth(status, read, jsz, func() time.Time { return time.Now().UTC() }), nil
+		}}
+}

modules/nats/cmd/nats-tools/main.go

@@ -182,5 +182,6 @@ func allTools() []stdio.Tool {
 	out := append(tools(monitor, ReadUsers, UsersWritten), removalTools(LiveBus(), SaidByTheRuntime, HeldInState)...)
 	out = append(out, expiryTools(LiveBus(), SaidByTheRuntime, RecordedBySeat)...)
 	out = append(out, brokerTools(HeldInState, jsz, StreamHistory(LiveBus()))...)
+	out = append(out, keeperHealthTool(StatusInState, HeldInState, jsz))
 	return append(out, requestTools(RequestsInState())...)
 }

modules/nats/module.json

@@ -119,7 +119,8 @@
     "nats_create",
     "nats_apply",
     "nats_recreate",
-    "nats_drop"
+    "nats_drop",
+    "nats_keeper_health"
   ],
   "guards": [
     8222