From 97e990c8f8df93c0d0aed84c1bec37f923cbe23b Mon Sep 17 00:00:00 2001
From: jochen <jschoubben@gmail.com>
Date: Wed, 11 Nov 2026 21:37:12 +0100
Subject: [PATCH] =?UTF-8?q?=C2=A7556:=20a=20reader=20of=20a=20stream=20kep?=
 =?UTF-8?q?t=20last=20per=20subject=20is=20granted=20its=20ordered=20consu?=
 =?UTF-8?q?mer?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Builds: design 47 G §556 (G-20 A-4)

Claude-Session: https://claude.ai/code/session_01JG73KEq4zoDfM9WtYpcQgZ
---
 .../internal/buscompose/modstreams.go         |  8 +++++++
 .../internal/buscompose/orderedread_test.go   | 23 +++++++++++++++++++
 2 files changed, 31 insertions(+)
 create mode 100644 modules/mesh-grants/internal/buscompose/orderedread_test.go

diff --git a/modules/mesh-grants/internal/buscompose/modstreams.go b/modules/mesh-grants/internal/buscompose/modstreams.go
index 64e0cec1..af945c1b 100644
--- a/modules/mesh-grants/internal/buscompose/modstreams.go
+++ b/modules/mesh-grants/internal/buscompose/modstreams.go
@@ -260,6 +260,14 @@ func heardGrants(p Principal, hears []Heard) []string {
 			"$JS.API.CONSUMER.INFO."+h.Stream+"."+durable,
 			"$JS.API.CONSUMER.MSG.NEXT."+h.Stream+"."+durable,
 			"$JS.ACK."+h.Stream+"."+durable+".>")
+		if h.LastPerSubject {
+			// A stream kept last per subject is read whole at each start through an ordered consumer, made for that one read
+			// and with no durable name: its creation, its next message, its info and the deletion of its own (design 47 G §556, A-4).
+			out = append(out,
+				"$JS.API.CONSUMER.CREATE."+h.Stream, "$JS.API.CONSUMER.CREATE."+h.Stream+".>",
+				"$JS.API.CONSUMER.MSG.NEXT."+h.Stream+".*", "$JS.API.CONSUMER.INFO."+h.Stream+".*",
+				"$JS.API.CONSUMER.DELETE."+h.Stream+".*")
+		}
 	}
 	return out
 }
diff --git a/modules/mesh-grants/internal/buscompose/orderedread_test.go b/modules/mesh-grants/internal/buscompose/orderedread_test.go
new file mode 100644
index 00000000..fc61c48f
--- /dev/null
+++ b/modules/mesh-grants/internal/buscompose/orderedread_test.go
@@ -0,0 +1,23 @@
+package buscompose
+
+import (
+	"slices"
+	"testing"
+)
+
+// A reader of a stream kept last per subject is granted what an ordered consumer of that stream uses, and a reader of
+// another stream only its own durable (design 47 G §556, A-4).
+func TestAReaderOfAStreamKeptLastPerSubjectIsGrantedItsOrderedConsumer(t *testing.T) {
+	p := Principal{Module: "m", Node: "a"}
+	ordered := []string{"$JS.API.CONSUMER.CREATE.S", "$JS.API.CONSUMER.MSG.NEXT.S.*", "$JS.API.CONSUMER.INFO.S.*", "$JS.API.CONSUMER.DELETE.S.*"}
+	last := heardGrants(p, []Heard{{Stream: "S", Filters: []string{"f"}, LastPerSubject: true}})
+	for _, w := range ordered {
+		if !slices.Contains(last, w) {
+			t.Errorf("a last-per-subject reader is not granted %s: %v", w, last)
+		}
+	}
+	plain := heardGrants(p, []Heard{{Stream: "S", Filters: []string{"f"}}})
+	if slices.Contains(plain, ordered[0]) {
+		t.Errorf("a reader of another stream is granted an ordered consumer: %v", plain)
+	}
+}