diff --git a/pkg/models/project.go b/pkg/models/project.go
index 65a5f1430..55a297b26 100644
--- a/pkg/models/project.go
+++ b/pkg/models/project.go
@@ -175,7 +175,7 @@ var FavoritesPseudoProject = Project{
 // @Failure 500 {object} models.Message "Internal error"
 // @Router /projects [get]
 func (p *Project) ReadAll(s *xorm.Session, a web.Auth, search string, page int, perPage int) (result interface{}, resultCount int, totalItems int64, err error) {
-	prs, resultCount, totalItems, err := getAllRawProjects(s, a, search, page, perPage, p.IsArchived)
+	prs, resultCount, totalItems, err := getAllRawProjects(s, a, search, page, perPage, p.IsArchived, false)
 	if err != nil {
 		return nil, 0, 0, err
 	}
@@ -216,7 +216,11 @@ func (p *Project) ReadAll(s *xorm.Session, a web.Auth, search string, page int,
 	return prs, resultCount, totalItems, err
 }
 
-func getAllRawProjects(s *xorm.Session, a web.Auth, search string, page int, perPage int, isArchived bool) (projects []*Project, resultCount int, totalItems int64, err error) {
+func getAllRawProjects(s *xorm.Session, a web.Auth, search string, page int, perPage int, isArchived, listAll bool) (projects []*Project, resultCount int, totalItems int64, err error) {
+	if listAll {
+		return getRawProjectsUnscoped(s, search, page, perPage, isArchived)
+	}
+
 	// Check if we're dealing with a share auth
 	shareAuth, is := a.(*LinkSharing)
 	if is {
@@ -265,6 +269,80 @@ func getAllRawProjects(s *xorm.Session, a web.Auth, search string, page int, per
 	return prs, resultCount, totalItems, err
 }
 
+// ListAllProjects returns every project with owners hydrated; callers must authorize since this bypasses the per-user permission filter.
+func ListAllProjects(s *xorm.Session, search string, page, perPage int, isArchived bool) (projects []*Project, resultCount int, totalItems int64, err error) {
+	projects, resultCount, totalItems, err = getAllRawProjects(s, nil, search, page, perPage, isArchived, true)
+	if err != nil {
+		return nil, 0, 0, err
+	}
+
+	ownerIDs := make([]int64, 0, len(projects))
+	for _, p := range projects {
+		ownerIDs = append(ownerIDs, p.OwnerID)
+	}
+	owners, err := user.GetUsersByIDs(s, ownerIDs)
+	if err != nil {
+		return nil, 0, 0, err
+	}
+	for _, p := range projects {
+		if o, ok := owners[p.OwnerID]; ok {
+			p.Owner = o
+		}
+	}
+
+	return projects, resultCount, totalItems, nil
+}
+
+func getRawProjectsUnscoped(s *xorm.Session, search string, page, perPage int, isArchived bool) (projects []*Project, resultCount int, totalItems int64, err error) {
+	limit, start := getLimitFromPageIndex(page, perPage)
+
+	conds := []builder.Cond{}
+	if !isArchived {
+		conds = append(conds, builder.Eq{"is_archived": false})
+	}
+	if search != "" {
+		ids := []int64{}
+		for _, val := range strings.Split(search, ",") {
+			v, parseErr := strconv.ParseInt(val, 10, 64)
+			if parseErr != nil {
+				log.Debugf("Project search string part '%s' is not a number: %s", val, parseErr)
+				continue
+			}
+			ids = append(ids, v)
+		}
+		if len(ids) > 0 {
+			conds = append(conds, builder.In("id", ids))
+		} else {
+			conds = append(conds, db.MultiFieldSearchWithTableAlias(
+				[]string{"title", "description", "identifier"},
+				search,
+				"",
+			))
+		}
+	}
+	var where = builder.Expr("1 = 1")
+	if len(conds) > 0 {
+		where = builder.And(conds...)
+	}
+
+	query := s.Where(where).OrderBy("id DESC")
+	if limit > 0 {
+		query = query.Limit(limit, start)
+	}
+
+	projects = []*Project{}
+	if err = query.Find(&projects); err != nil {
+		return nil, 0, 0, err
+	}
+
+	totalItems, err = s.Where(where).Count(&Project{})
+	if err != nil {
+		return nil, 0, 0, err
+	}
+
+	return projects, len(projects), totalItems, nil
+}
+
 // ReadOne gets one project by its ID
 // @Summary Gets one project
 // @Description Returns a project by its ID.
@@ -1000,6 +1078,20 @@ func CreateNewProjectForUser(s *xorm.Session, u *user.User) (err error) {
 	return err
 }
 
+// RegisterUser creates a user plus their default inbox project; shared by /register and the admin create-user route.
+func RegisterUser(s *xorm.Session, u *user.User) (*user.User, error) {
+	newUser, err := user.CreateUser(s, u)
+	if err != nil {
+		return nil, err
+	}
+
+	if err := CreateNewProjectForUser(s, newUser); err != nil {
+		return nil, err
+	}
+
+	return newUser, nil
+}
+
 func UpdateProject(s *xorm.Session, project *Project, auth web.Auth, updateProjectBackground bool) (err error) {
 	err = checkProjectBeforeUpdateOrDelete(s, project)
 	if err != nil {
diff --git a/pkg/user/error.go b/pkg/user/error.go
index 88df428d6..1013a9e2d 100644
--- a/pkg/user/error.go
+++ b/pkg/user/error.go
@@ -767,3 +767,28 @@ func (err ErrTokenUserMismatch) HTTPError() web.HTTPError {
 		Message:  "This deletion token does not belong to your account.",
 	}
 }
+
+// ErrLastAdmin represents a "LastAdmin" kind of error.
+type ErrLastAdmin struct{}
+
+// IsErrLastAdmin checks if an error is a ErrLastAdmin.
+func IsErrLastAdmin(err error) bool {
+	_, ok := err.(ErrLastAdmin)
+	return ok
+}
+
+func (err ErrLastAdmin) Error() string {
+	return "Cannot remove the last remaining instance admin"
+}
+
+// ErrCodeLastAdmin holds the unique world-error code of this error
+const ErrCodeLastAdmin = 1030
+
+// HTTPError holds the http error description
+func (err ErrLastAdmin) HTTPError() web.HTTPError {
+	return web.HTTPError{
+		HTTPCode: http.StatusBadRequest,
+		Code:     ErrCodeLastAdmin,
+		Message:  "Cannot remove the last remaining instance admin.",
+	}
+}
diff --git a/pkg/user/is_admin_test.go b/pkg/user/is_admin_test.go
index 2d49ba3d8..f173e18f7 100644
--- a/pkg/user/is_admin_test.go
+++ b/pkg/user/is_admin_test.go
@@ -21,6 +21,7 @@ import (
 
 	"code.vikunja.io/api/pkg/db"
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 func TestUser_IsAdminField(t *testing.T) {
@@ -30,6 +31,6 @@ func TestUser_IsAdminField(t *testing.T) {
 
 	u := &User{ID: 1}
 	_, err := s.Get(u)
-	assert.NoError(t, err)
+	require.NoError(t, err)
 	assert.False(t, u.IsAdmin, "fixture user 1 should not be admin by default")
 }
diff --git a/pkg/user/user.go b/pkg/user/user.go
index 00d525653..96863f398 100644
--- a/pkg/user/user.go
+++ b/pkg/user/user.go
@@ -37,6 +37,7 @@ import (
 	"golang.org/x/crypto/bcrypt"
 	"xorm.io/builder"
 	"xorm.io/xorm"
+	"xorm.io/xorm/schemas"
 )
 
 // IsErrUserStatusError returns true if the error is an ErrAccountDisabled or ErrAccountLocked.
@@ -94,7 +95,6 @@ type User struct {
 
 	Status Status `xorm:"default 0" json:"-"`
 
-	// Whether this user is a site-wide admin. Managed via CLI only.
 	IsAdmin bool `xorm:"not null default false" json:"-"`
 
 	AvatarProvider string `xorm:"varchar(255) null" json:"-"`
@@ -664,6 +664,30 @@ func SetUserStatus(s *xorm.Session, user *User, status Status) (err error) {
 	return
 }
 
+// GuardLastAdmin refuses demoting or deleting the last reachable admin; only active, non-deletion-scheduled admins count since the rest cannot log in.
+// SELECT ... FOR UPDATE closes the TOCTOU race between concurrent demotions on MySQL (xorm only emits it for MySQL; SQLite serializes writes, postgres relies on serializable isolation).
+func GuardLastAdmin(s *xorm.Session, target *User) error {
+	if !target.IsAdmin {
+		return nil
+	}
+
+	session := s.Where("is_admin = ?", true).
+		And("status = ?", StatusActive).
+		And("deletion_scheduled_at IS NULL")
+	if db.Type() == schemas.MYSQL {
+		session = session.ForUpdate()
+	}
+
+	count, err := session.Count(&User{})
+	if err != nil {
+		return err
+	}
+	if count <= 1 {
+		return ErrLastAdmin{}
+	}
+	return nil
+}
+
 // UpdateUserPassword updates the password of a user
 func UpdateUserPassword(s *xorm.Session, user *User, newPassword string) (err error) {
 
diff --git a/pkg/user/user_claims_test.go b/pkg/user/user_claims_test.go
index 4baab96b2..07b595aa2 100644
--- a/pkg/user/user_claims_test.go
+++ b/pkg/user/user_claims_test.go
@@ -21,6 +21,7 @@ import (
 
 	"github.com/golang-jwt/jwt/v5"
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 func TestGetUserFromClaims_IsAdmin(t *testing.T) {
@@ -30,7 +31,7 @@ func TestGetUserFromClaims_IsAdmin(t *testing.T) {
 		"is_admin": true,
 	}
 	u, err := GetUserFromClaims(claims)
-	assert.NoError(t, err)
+	require.NoError(t, err)
 	assert.True(t, u.IsAdmin)
 }
 
@@ -40,6 +41,6 @@ func TestGetUserFromClaims_IsAdminMissing(t *testing.T) {
 		"username": "u1",
 	}
 	u, err := GetUserFromClaims(claims)
-	assert.NoError(t, err)
+	require.NoError(t, err)
 	assert.False(t, u.IsAdmin)
 }
diff --git a/pkg/yaegi_symbols/vikunja_models.go b/pkg/yaegi_symbols/vikunja_models.go
index ab731b285..f33da550c 100644
--- a/pkg/yaegi_symbols/vikunja_models.go
+++ b/pkg/yaegi_symbols/vikunja_models.go
@@ -258,6 +258,7 @@ func init() {
 		"RegisterOverdueReminderCron":                      reflect.ValueOf(models.RegisterOverdueReminderCron),
 		"RegisterReminderCron":                             reflect.ValueOf(models.RegisterReminderCron),
 		"RegisterSessionCleanupCron":                       reflect.ValueOf(models.RegisterSessionCleanupCron),
+		"RegisterUser":                                     reflect.ValueOf(models.RegisterUser),
 		"RegisterUserDeletionCron":                         reflect.ValueOf(models.RegisterUserDeletionCron),
 		"RegisterUserDirectedEventForWebhook":              reflect.ValueOf(models.RegisterUserDirectedEventForWebhook),
 		"RelationKindBlocked":                              reflect.ValueOf(models.RelationKindBlocked),