fix: resolve P1 backend consistency issues

server/topic_test.go

@@ -3,6 +3,7 @@ package main
 import (
 	"context"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"net/http"
 	"os"
@@ -941,6 +942,9 @@ func TestHandleBroadcastDataRejectsMentionAllByMember(t *testing.T) {
 	pud.modeWant = types.ModeCPublic
 	pud.modeGiven = types.ModeCPublic
 	helper.topic.perUser[helper.uids[0]] = pud
+	helper.ss.EXPECT().Get(types.TenantID(1), "grp-test", helper.uids[0], false).Return(&types.Subscription{
+		TenantID: 1, Topic: "grp-test", User: helper.uids[0].String(), ModeWant: types.ModeCPublic, ModeGiven: types.ModeCPublic,
+	}, nil)
 
 	from := helper.uids[0].UserId()
 	msg := &ClientComMessage{
@@ -963,6 +967,39 @@ func TestHandleBroadcastDataRejectsMentionAllByMember(t *testing.T) {
 	}
 }
 
+func TestValidateMessageReplacementChecksAuthorAndWindow(t *testing.T) {
+	ctrl := gomock.NewController(t)
+	defer ctrl.Finish()
+	oldMessages := store.Messages
+	messages := mock_store.NewMockMessagesPersistenceInterface(ctrl)
+	store.Messages = messages
+	t.Cleanup(func() { store.Messages = oldMessages })
+
+	now := time.Date(2026, 9, 6, 10, 0, 0, 0, time.UTC)
+	topic := &Topic{tenantID: 7, name: "grpAlpha"}
+	author := types.Uid(42)
+	messages.EXPECT().GetOne(types.TenantID(7), "grpAlpha", int64(8)).Return(&types.Message{
+		Topic: "grpAlpha", SeqId: 8, From: author.String(), ObjHeader: types.ObjHeader{CreatedAt: now.Add(-time.Minute)},
+	}, nil)
+	if err := topic.validateMessageReplacement(author, map[string]any{"replace": ":8"}, now); err != nil {
+		t.Fatalf("valid replacement rejected: %v", err)
+	}
+
+	messages.EXPECT().GetOne(types.TenantID(7), "grpAlpha", int64(9)).Return(&types.Message{
+		Topic: "grpAlpha", SeqId: 9, From: types.Uid(99).String(), ObjHeader: types.ObjHeader{CreatedAt: now.Add(-time.Minute)},
+	}, nil)
+	if err := topic.validateMessageReplacement(author, map[string]any{"replace": ":9"}, now); !errors.Is(err, types.ErrPermissionDenied) {
+		t.Fatalf("replacement of peer message: got %v", err)
+	}
+
+	messages.EXPECT().GetOne(types.TenantID(7), "grpAlpha", int64(10)).Return(&types.Message{
+		Topic: "grpAlpha", SeqId: 10, From: author.String(), ObjHeader: types.ObjHeader{CreatedAt: now.Add(-6 * time.Minute)},
+	}, nil)
+	if err := topic.validateMessageReplacement(author, map[string]any{"replace": ":10"}, now); !errors.Is(err, types.ErrPermissionDenied) {
+		t.Fatalf("expired replacement: got %v", err)
+	}
+}
+
 func TestHandleBroadcastDataFiltersInvalidMentions(t *testing.T) {
 	numUsers := 2
 	helper := TopicTestHelper{}