diff --git a/go-backend/internal/store/repo/repository.go b/go-backend/internal/store/repo/repository.go
index a0b199f..00381a0 100644
--- a/go-backend/internal/store/repo/repository.go
+++ b/go-backend/internal/store/repo/repository.go
@@ -2375,14 +2375,20 @@ func (r *Repository) Import(backup *model.BackupData, types []string) (*model.Im
 		typeSet[t] = true
 	}
 
-	err := r.db.Transaction(func(tx *gorm.DB) error {
-		// Lock in a stable order before touching either membership.
-		if typeSet["users"] {
+	err := backupImportTransaction(r.db, func(tx *gorm.DB) error {
+		result = &model.ImportResult{}
+		tables, err := lockPostgresBackupTables(tx, backup, typeSet)
+		if err != nil {
+			return err
+		}
+		// SQLite still needs its writer reservation for display order.
+		// PostgreSQL membership locks were taken with all imported tables above.
+		if tx.Dialector.Name() != "postgres" && typeSet["users"] {
 			if err := lockDisplayOrder(tx, "user"); err != nil {
 				return err
 			}
 		}
-		if typeSet["speedLimits"] {
+		if tx.Dialector.Name() != "postgres" && typeSet["speedLimits"] {
 			if err := lockDisplayOrder(tx, "speed_limit"); err != nil {
 				return err
 			}
@@ -2459,7 +2465,7 @@ func (r *Repository) Import(backup *model.BackupData, types []string) (*model.Im
 			}
 			result.ConfigsImported = count
 		}
-		return nil
+		return advancePostgresBackupSequences(tx, tables)
 	})
 	if err != nil {
 		return nil, err
diff --git a/go-backend/internal/store/repo/repository_backup_postgres.go b/go-backend/internal/store/repo/repository_backup_postgres.go
new file mode 100644
index 0000000..238437a
--- /dev/null
+++ b/go-backend/internal/store/repo/repository_backup_postgres.go
@@ -0,0 +1,195 @@
+package repo
+
+import (
+	"errors"
+	"fmt"
+	"time"
+
+	"go-backend/internal/store/model"
+
+	"gorm.io/gorm"
+)
+
+var errBackupImportBusy = errors.New("database is busy; retry the backup import")
+
+// Only retry lock acquisition failures, which occur before any backup writes.
+// NOWAIT releases partial lock sets instead of deadlocking with existing
+// child-before-parent deletes or forward-before-user traffic updates.
+func backupImportTransaction(db *gorm.DB, importRows func(*gorm.DB) error) error {
+	var err error
+	for attempt := 0; attempt < 10; attempt++ {
+		err = db.Transaction(importRows)
+		if !errors.Is(err, errBackupImportBusy) {
+			return err
+		}
+		if attempt < 9 {
+			time.Sleep(min(10*time.Millisecond<<attempt, 100*time.Millisecond))
+		}
+	}
+	return err
+}
+
+// Lock every table that import can write, including generated-ID child tables.
+// No writes happen until the complete set is held. Existing CRUD transactions
+// can therefore finish regardless of their own parent/child mutation order.
+// The returned subset contains only tables receiving explicit backup IDs.
+func lockPostgresBackupTables(tx *gorm.DB, backup *model.BackupData, types map[string]bool) ([]string, error) {
+	if tx.Dialector.Name() != "postgres" {
+		return nil, nil
+	}
+	chains, grants, ports := 0, 0, 0
+	for _, tunnel := range backup.Tunnels {
+		chains += len(tunnel.ChainTunnels)
+	}
+	for _, permission := range backup.Permissions {
+		grants += len(permission.Grants)
+	}
+	for _, forward := range backup.Forwards {
+		if forward.ForwardPorts != nil {
+			ports++
+		}
+	}
+	var tables []string
+	for _, item := range []struct {
+		kind        string
+		count       int
+		name        string
+		explicitIDs bool
+	}{
+		{"users", len(backup.Users), "user", true},
+		{"speedLimits", len(backup.SpeedLimits), "speed_limit", true},
+		{"nodes", len(backup.Nodes), "node", true},
+		{"tunnels", len(backup.Tunnels), "tunnel", true},
+		{"tunnels", chains, "chain_tunnel", true},
+		{"forwards", len(backup.Forwards), "forward", true},
+		{"userTunnels", len(backup.UserTunnels), "user_tunnel", true},
+		{"tunnelGroups", len(backup.TunnelGroups), "tunnel_group", true},
+		{"userGroups", len(backup.UserGroups), "user_group", true},
+		{"permissions", len(backup.Permissions), "group_permission", true},
+		{"permissions", grants, "group_permission_grant", true},
+		{"users", len(backup.Users), "user_quota", false},
+		{"forwards", ports, "forward_port", false},
+		{"tunnelGroups", len(backup.TunnelGroups), "tunnel_group_tunnel", false},
+		{"userGroups", len(backup.UserGroups), "user_group_user", false},
+		{"configs", len(FilterBackupConfigs(backup.Configs)), "vite_config", false},
+	} {
+		if !types[item.kind] || item.count == 0 {
+			continue
+		}
+		// Resolve the same relation as normal unqualified repository queries,
+		// even when the first search_path schema has no copy of this table.
+		var relation struct {
+			Schema string
+			Name   string
+		}
+		if err := tx.Raw(`SELECT n.nspname AS schema, c.relname AS name
+			FROM pg_catalog.pg_class c JOIN pg_catalog.pg_namespace n ON n.oid = c.relnamespace
+			WHERE c.oid = pg_catalog.to_regclass(?)`, quoteSQLIdentifier(item.name)).Scan(&relation).Error; err != nil {
+			return nil, err
+		}
+		if relation.Name == "" {
+			return nil, fmt.Errorf("missing import table %s", item.name)
+		}
+		table := quoteSQLIdentifier(relation.Schema) + "." + quoteSQLIdentifier(relation.Name)
+		if err := tx.Exec("LOCK TABLE " + table + " IN SHARE ROW EXCLUSIVE MODE NOWAIT").Error; err != nil {
+			var pgError interface{ SQLState() string }
+			if errors.As(err, &pgError) && pgError.SQLState() == "55P03" {
+				return nil, fmt.Errorf("%w: %w", errBackupImportBusy, err)
+			}
+			return nil, err
+		}
+		if item.explicitIDs {
+			tables = append(tables, table)
+		}
+	}
+	return tables, nil
+}
+
+func advancePostgresBackupSequences(tx *gorm.DB, tables []string) error {
+	for _, table := range tables {
+		if err := advancePostgresBackupSequence(tx, table); err != nil {
+			return fmt.Errorf("advance imported %s id sequence: %w", table, err)
+		}
+	}
+	return nil
+}
+
+// The caller holds the table's SHARE ROW EXCLUSIVE lock until commit. Unlike
+// startup's setval repair, RESTART is transactional and invalidates other
+// connections' cached values. Never return to IDs already allocated, even if
+// their rows were deleted or their transactions rolled back.
+func advancePostgresBackupSequence(tx *gorm.DB, table string) error {
+	var maxID int64
+	if err := tx.Raw("SELECT COALESCE(MAX(id), 0) FROM " + table).Scan(&maxID).Error; err != nil {
+		return err
+	}
+	if maxID <= 0 {
+		return nil
+	}
+	type sequenceInfo struct {
+		Schema    string
+		Name      string
+		Cache     int64
+		Increment int64
+		Maximum   int64
+	}
+	var sequences []sequenceInfo
+	// Prefer the actual default's catalog dependency: a legacy custom nextval
+	// default need not own its sequence, and the old owned serial may remain.
+	// Identity columns have no pg_attrdef, so use their owned sequence instead.
+	if err := tx.Raw(`WITH defaults AS (
+		SELECT dep.refobjid AS oid FROM pg_catalog.pg_attrdef def
+		JOIN pg_catalog.pg_attribute attr ON attr.attrelid = def.adrelid AND attr.attnum = def.adnum
+		JOIN pg_catalog.pg_depend dep ON dep.classid = 'pg_catalog.pg_attrdef'::regclass
+			AND dep.objid = def.oid AND dep.refclassid = 'pg_catalog.pg_class'::regclass
+		JOIN pg_catalog.pg_sequence seq ON seq.seqrelid = dep.refobjid
+		WHERE def.adrelid = ?::regclass AND attr.attname = 'id'
+	), candidates AS (
+		SELECT oid FROM defaults
+		UNION SELECT pg_catalog.pg_get_serial_sequence(?, 'id')::regclass WHERE NOT EXISTS (SELECT 1 FROM defaults)
+	)
+	SELECT n.nspname AS schema, c.relname AS name,
+		s.seqcache AS cache, s.seqincrement AS increment, s.seqmax AS maximum
+		FROM pg_catalog.pg_sequence s
+		JOIN pg_catalog.pg_class c ON c.oid = s.seqrelid
+		JOIN pg_catalog.pg_namespace n ON n.oid = c.relnamespace
+		WHERE s.seqrelid IN (SELECT oid FROM candidates)`, table, table).Scan(&sequences).Error; err != nil {
+		return err
+	}
+	if len(sequences) != 1 || sequences[0].Increment <= 0 {
+		return fmt.Errorf("missing or ambiguous ascending ID sequence")
+	}
+	sequence := sequences[0]
+	name := quoteSQLIdentifier(sequence.Schema) + "." + quoteSQLIdentifier(sequence.Name)
+	// Reapplying CACHE without changing its setting takes a sequence DDL lock.
+	// Read last_value only after that lock: even direct concurrent nextval calls
+	// must finish first. The table locks already exclude normal INSERTs.
+	if err := tx.Exec(fmt.Sprintf("ALTER SEQUENCE %s CACHE %d", name, sequence.Cache)).Error; err != nil {
+		return err
+	}
+	var state struct {
+		LastValue int64
+		IsCalled  bool
+	}
+	if err := tx.Raw("SELECT last_value, is_called FROM " + name).Scan(&state).Error; err != nil {
+		return err
+	}
+	if state.LastValue < 1 {
+		return fmt.Errorf("ID sequence must allocate positive IDs")
+	}
+	if maxID >= sequence.Maximum || (state.IsCalled && state.LastValue > sequence.Maximum-sequence.Increment) {
+		return fmt.Errorf("ID sequence exhausted")
+	}
+	next := state.LastValue
+	if state.IsCalled {
+		next += sequence.Increment
+	}
+	if next <= maxID {
+		steps := (maxID-next)/sequence.Increment + 1
+		if steps > (sequence.Maximum-next)/sequence.Increment {
+			return fmt.Errorf("ID sequence exhausted")
+		}
+		next += steps * sequence.Increment
+	}
+	return tx.Exec(fmt.Sprintf("ALTER SEQUENCE %s RESTART WITH %d", name, next)).Error
+}
diff --git a/go-backend/tests/contract/postgres_backup_sequences_test.go b/go-backend/tests/contract/postgres_backup_sequences_test.go
new file mode 100644
index 0000000..35c6389
--- /dev/null
+++ b/go-backend/tests/contract/postgres_backup_sequences_test.go
@@ -0,0 +1,554 @@
+package contract_test
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"slices"
+	"strconv"
+	"strings"
+	"testing"
+	"time"
+
+	"go-backend/internal/auth"
+	httpserver "go-backend/internal/http"
+	"go-backend/internal/http/handler"
+	"go-backend/internal/security"
+	"go-backend/internal/store/model"
+	"go-backend/internal/store/repo"
+)
+
+func TestPostgresBackupImportAllowsImmediateCreate(t *testing.T) {
+	source := ownerNamesRepository(t, "postgres")()
+	for _, name := range []string{"backup-one", "backup-two"} {
+		if _, err := source.CreateUser(name, security.MD5("test-password"), 1, 0, 10, 1, 2, 1, 3, 0); err != nil {
+			t.Fatal(err)
+		}
+		if _, err := source.CreateSpeedLimit(name, 100, 0, 1); err != nil {
+			t.Fatal(err)
+		}
+	}
+	backup, err := source.ExportAll()
+	if err != nil {
+		t.Fatal(err)
+	}
+	target := ownerNamesRepository(t, "postgres")()
+	if _, err := target.Import(backup, []string{"users", "speedLimits"}); err != nil {
+		t.Fatal(err)
+	}
+	if id, err := target.CreateUser("after-import", security.MD5("test-password"), 1, 0, 10, 1, 2, 1, 3, 0); err != nil || id <= 2 {
+		t.Errorf("create user immediately after backup import: id=%d err=%v", id, err)
+	}
+	if id, err := target.CreateSpeedLimit("after-import", 100, 0, 1); err != nil || id <= 2 {
+		t.Errorf("create speed limit immediately after backup import: id=%d err=%v", id, err)
+	}
+}
+
+func TestPostgresBackupImportPreservesAllocatedIDs(t *testing.T) {
+	for _, called := range []bool{false, true} {
+		t.Run(fmt.Sprintf("called=%t", called), func(t *testing.T) {
+			r := ownerNamesRepository(t, "postgres")()
+			// A deleted or rolled-back allocation may be higher than every row.
+			for _, table := range []string{"user", "speed_limit"} {
+				if err := r.DB().Exec(`SELECT setval(pg_get_serial_sequence(?, 'id'), 500, ?)`, `"`+table+`"`, called).Error; err != nil {
+					t.Fatal(err)
+				}
+			}
+			b := &model.BackupData{Users: []model.UserBackup{{ID: 1, User: "restored", Pwd: "$2-test-fixture", RoleID: 1}}, SpeedLimits: []model.SpeedLimitBackup{{ID: 1, Name: "restored"}}}
+			if _, err := r.Import(b, []string{"users", "speedLimits"}); err != nil {
+				t.Fatal(err)
+			}
+			want := int64(500)
+			if called {
+				want++
+			}
+			if id, err := r.CreateUser("new", "hash", 1, 0, 0, 0, 0, 1, 0, 0); err != nil || id != want {
+				t.Fatalf("user id=%d, want %d; err=%v", id, want, err)
+			}
+			if id, err := r.CreateSpeedLimit("new", 100, 0, 1); err != nil || id != want {
+				t.Fatalf("speed limit id=%d, want %d; err=%v", id, want, err)
+			}
+		})
+	}
+}
+
+func TestPostgresBackupImportInvalidatesCachedIDs(t *testing.T) {
+	r := ownerNamesRepository(t, "postgres")()
+	if err := r.DB().Exec(`ALTER SEQUENCE speed_limit_id_seq CACHE 20`).Error; err != nil {
+		t.Fatal(err)
+	}
+	pool, err := r.DB().DB()
+	if err != nil {
+		t.Fatal(err)
+	}
+	cached, err := pool.Conn(context.Background())
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer cached.Close()
+	// Hold this backend out of the pool with unused cached IDs 2..20.
+	var allocated int64
+	if err := cached.QueryRowContext(context.Background(), `SELECT nextval('speed_limit_id_seq')`).Scan(&allocated); err != nil {
+		t.Fatal(err)
+	}
+	if allocated != 1 {
+		t.Fatal(allocated)
+	}
+	b := &model.BackupData{SpeedLimits: []model.SpeedLimitBackup{{ID: 2, Name: "restored"}}}
+	if _, err := r.Import(b, []string{"speedLimits"}); err != nil {
+		t.Fatal(err)
+	}
+	// Return only the cached backend to the pool, so the public create must use it.
+	pool.SetMaxIdleConns(0)
+	pool.SetMaxIdleConns(1)
+	if err := cached.Close(); err != nil {
+		t.Fatal(err)
+	}
+	if id, err := r.CreateSpeedLimit("new", 100, 0, 1); err != nil || id <= 20 {
+		t.Fatalf("cached ID reused: id=%d err=%v", id, err)
+	}
+}
+
+func TestPostgresBackupImportRollsBackSequenceOnCommitFailure(t *testing.T) {
+	r := ownerNamesRepository(t, "postgres")()
+	// Deferred validation fails after import has already advanced the sequence.
+	for _, query := range []string{
+		`CREATE FUNCTION reject_import_commit() RETURNS trigger LANGUAGE plpgsql AS $$ BEGIN RAISE EXCEPTION 'reject imported row at commit'; END $$`,
+		`CREATE CONSTRAINT TRIGGER reject_import_commit AFTER INSERT ON speed_limit DEFERRABLE INITIALLY DEFERRED FOR EACH ROW WHEN (NEW.name = 'fail-at-commit') EXECUTE FUNCTION reject_import_commit()`,
+	} {
+		if err := r.DB().Exec(query).Error; err != nil {
+			t.Fatal(err)
+		}
+	}
+	b := &model.BackupData{SpeedLimits: []model.SpeedLimitBackup{{ID: 100, Name: "fail-at-commit"}}}
+	if _, err := r.Import(b, []string{"speedLimits"}); err == nil || !strings.Contains(err.Error(), "reject imported row at commit") {
+		t.Fatalf("expected commit failure, got %v", err)
+	}
+	exported, err := r.ExportAll()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(exported.SpeedLimits) != 0 {
+		t.Fatal("failed import persisted rows")
+	}
+	if id, err := r.CreateSpeedLimit("after-failure", 100, 0, 1); err != nil || id != 1 {
+		t.Fatalf("failed import changed next allocation: id=%d err=%v", id, err)
+	}
+}
+
+func TestPostgresBackupImportPreservesSequenceIncrement(t *testing.T) {
+	r := ownerNamesRepository(t, "postgres")()
+	if err := r.DB().Exec(`ALTER SEQUENCE speed_limit_id_seq INCREMENT BY 10`).Error; err != nil {
+		t.Fatal(err)
+	}
+	b := &model.BackupData{SpeedLimits: []model.SpeedLimitBackup{{ID: 25, Name: "restored"}}}
+	if _, err := r.Import(b, []string{"speedLimits"}); err != nil {
+		t.Fatal(err)
+	}
+	if id, err := r.CreateSpeedLimit("new", 100, 0, 1); err != nil || id != 31 {
+		t.Fatalf("changed ID progression: id=%d, want 31; err=%v", id, err)
+	}
+}
+
+func TestPostgresBackupImportAdvancesEveryExplicitIDTable(t *testing.T) {
+	source := ownerNamesRepository(t, "postgres")()
+	types := []string{"users", "speedLimits", "nodes", "tunnels", "forwards", "userTunnels", "tunnelGroups", "userGroups", "permissions", "configs"}
+	fixture := &model.BackupData{
+		Users:        []model.UserBackup{{ID: 1, User: "old", Pwd: "$2-test-fixture", RoleID: 1}},
+		SpeedLimits:  []model.SpeedLimitBackup{{ID: 1, Name: "old"}},
+		Nodes:        []model.NodeBackup{{ID: 1, Name: "old", Secret: "old-node"}},
+		Tunnels:      []model.TunnelBackup{{ID: 1, Name: "old", ChainTunnels: []model.ChainTunnelBackup{{ID: 1, TunnelID: 1, NodeID: 1, ChainType: "1"}}}},
+		Forwards:     []model.ForwardBackup{{ID: 1, Name: "old", UserID: 1, TunnelID: 1}},
+		UserTunnels:  []model.UserTunnelBackup{{ID: 1, UserID: 1, TunnelID: 1}},
+		TunnelGroups: []model.TunnelGroupBackup{{ID: 1, Name: "old"}},
+		UserGroups:   []model.UserGroupBackup{{ID: 1, Name: "old"}},
+		Permissions:  []model.PermissionBackup{{ID: 1, UserGroupID: 1, TunnelGroupID: 1, Grants: []model.PermissionGrantBackup{{ID: 1, UserGroupID: 1, TunnelGroupID: 1, UserTunnelID: 1}}}},
+	}
+	if _, err := source.Import(fixture, types); err != nil {
+		t.Fatal(err)
+	}
+	backup, err := source.ExportAll()
+	if err != nil {
+		t.Fatal(err)
+	}
+	r := ownerNamesRepository(t, "postgres")()
+	if _, err := r.Import(backup, types); err != nil {
+		t.Fatal(err)
+	}
+	// Use the normal public creation methods, including the nested child tables.
+	for _, create := range []struct {
+		name string
+		run  func() error
+	}{
+		{"user", func() error { _, err := r.CreateUser("new", "hash", 1, 0, 0, 0, 0, 1, 0, 0); return err }},
+		{"speed limit", func() error { _, err := r.CreateSpeedLimit("new", 100, 0, 1); return err }},
+		{"node", func() error {
+			return r.CreateRemoteNode("new", "new-node", "127.0.0.1", "10000-20000", 0, 1, 0, "", "", "")
+		}},
+		{"tunnel", func() error { _, err := r.CreateTunnelTx(r.DB(), "new", 1, 1, 0, 0, 1, nil, 0, "", "", 0); return err }},
+		{"chain tunnel", func() error { return r.CreateChainTunnelTx(r.DB(), 1, "1", 2, sql.NullInt64{}, "", 1, "tls", "") }},
+		{"forward", func() error {
+			_, err := r.CreateForwardTx(1, "old", "new", 1, "127.0.0.1:80", "", 0, 0, nil, 0, "", nil, 0, 0, nil, 0, 0, 0)
+			return err
+		}},
+		{"user tunnel", func() error { return r.InsertUserTunnel(2, 1, nil, 0, 0, 0, 0, 1) }},
+		{"tunnel group", func() error { return r.GroupCreate("tunnel_group", "new", 1, 0) }},
+		{"user group", func() error { return r.GroupCreate("user_group", "new", 1, 0) }},
+		{"permission", func() error { return r.InsertGroupPermission(2, 2, 0) }},
+		{"permission grant", func() error { r.InsertGroupPermissionGrant(1, 1, 2, 1, 0); return nil }},
+	} {
+		t.Run(create.name, func(t *testing.T) {
+			if err := create.run(); err != nil {
+				t.Fatal(err)
+			}
+		})
+	}
+	got, err := r.ExportAll()
+	if err != nil {
+		t.Fatal(err)
+	}
+	ids := map[string][]int64{}
+	for _, v := range got.Users {
+		ids["user"] = append(ids["user"], v.ID)
+	}
+	for _, v := range got.SpeedLimits {
+		ids["speed limit"] = append(ids["speed limit"], v.ID)
+	}
+	for _, v := range got.Nodes {
+		ids["node"] = append(ids["node"], v.ID)
+	}
+	for _, v := range got.Tunnels {
+		ids["tunnel"] = append(ids["tunnel"], v.ID)
+		for _, child := range v.ChainTunnels {
+			ids["chain tunnel"] = append(ids["chain tunnel"], child.ID)
+		}
+	}
+	for _, v := range got.Forwards {
+		ids["forward"] = append(ids["forward"], v.ID)
+	}
+	for _, v := range got.UserTunnels {
+		ids["user tunnel"] = append(ids["user tunnel"], v.ID)
+	}
+	for _, v := range got.TunnelGroups {
+		ids["tunnel group"] = append(ids["tunnel group"], v.ID)
+	}
+	for _, v := range got.UserGroups {
+		ids["user group"] = append(ids["user group"], v.ID)
+	}
+	for _, v := range got.Permissions {
+		ids["permission"] = append(ids["permission"], v.ID)
+		for _, child := range v.Grants {
+			ids["permission grant"] = append(ids["permission grant"], child.ID)
+		}
+	}
+	if len(ids) != 11 {
+		t.Fatalf("missing tables in export: %v", ids)
+	}
+	for name, values := range ids {
+		slices.Sort(values)
+		if !slices.Equal(values, []int64{1, 2}) {
+			t.Errorf("%s: expected old and new IDs [1 2], got %v", name, values)
+		}
+	}
+}
+
+func TestPostgresBackupImportKeepsExistingRowsAndEmptySelections(t *testing.T) {
+	r := ownerNamesRepository(t, "postgres")()
+	// Fixture simulates an existing explicit-ID row with an unsynchronized sequence.
+	if err := r.DB().Create(&model.SpeedLimit{ID: 500, Name: "existing"}).Error; err != nil {
+		t.Fatal(err)
+	}
+	old := &model.BackupData{SpeedLimits: []model.SpeedLimitBackup{{ID: 1, Name: "legacy"}}}
+	if _, err := r.Import(old, []string{"speedLimits"}); err != nil {
+		t.Fatal(err)
+	}
+	if id, err := r.CreateSpeedLimit("new", 100, 0, 1); err != nil || id != 501 {
+		t.Fatalf("existing maximum ignored: id=%d err=%v", id, err)
+	}
+	for _, b := range []*model.BackupData{{}, {Users: []model.UserBackup{{ID: 900, User: "not-selected", Pwd: "$2-test-fixture"}}}} {
+		if _, err := r.Import(b, []string{"speedLimits"}); err != nil {
+			t.Fatal(err)
+		}
+	}
+	if id, err := r.CreateUser("first-user", "hash", 1, 0, 0, 0, 0, 1, 0, 0); err != nil || id != 2 {
+		t.Fatalf("unselected sequence changed: id=%d err=%v", id, err)
+	}
+	if id, err := r.CreateSpeedLimit("after-empty", 100, 0, 1); err != nil || id != 502 {
+		t.Fatalf("empty import changed allocation: id=%d err=%v", id, err)
+	}
+	got, err := r.ExportAll()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(got.Users) != 2 || len(got.SpeedLimits) != 4 || got.SpeedLimits[1].Name != "existing" {
+		t.Fatalf("existing or unselected data changed: %+v", got)
+	}
+}
+
+func TestPostgresBackupImportResolvesLegacySequenceAndSearchPath(t *testing.T) {
+	r := ownerNamesRepository(t, "postgres")()
+	pool, err := r.DB().DB()
+	if err != nil {
+		t.Fatal(err)
+	}
+	pool.SetMaxOpenConns(1)
+	var schema string
+	if err := r.DB().Raw(`SELECT current_schema()`).Scan(&schema).Error; err != nil {
+		t.Fatal(err)
+	}
+	prefix := "Empty-Prefix-" + strconv.FormatInt(time.Now().UnixNano(), 36)
+	if err := r.DB().Exec(`CREATE SCHEMA "` + prefix + `"`).Error; err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() { _ = r.DB().Exec(`DROP SCHEMA "` + prefix + `" CASCADE`).Error })
+	// The historical default uses a custom, unowned sequence; the original
+	// owned serial sequence still exists but is no longer used by INSERT.
+	for _, query := range []string{
+		`CREATE SEQUENCE "Custom Limit Sequence"`,
+		`ALTER TABLE speed_limit ALTER COLUMN id SET DEFAULT nextval('"Custom Limit Sequence"'::regclass)`,
+		`SET search_path TO "` + prefix + `", "` + schema + `"`,
+	} {
+		if err := r.DB().Exec(query).Error; err != nil {
+			t.Fatal(err)
+		}
+	}
+	b := &model.BackupData{SpeedLimits: []model.SpeedLimitBackup{{ID: 1, Name: "legacy"}}}
+	if _, err := r.Import(b, []string{"speedLimits"}); err != nil {
+		t.Fatal(err)
+	}
+	if id, err := r.CreateSpeedLimit("new", 100, 0, 1); err != nil || id != 2 {
+		t.Fatalf("wrong sequence or schema: id=%d err=%v", id, err)
+	}
+}
+
+func waitForBackupDBCondition(t *testing.T, r *repo.Repository, query string, args ...interface{}) {
+	t.Helper()
+	deadline := time.Now().Add(3 * time.Second)
+	for time.Now().Before(deadline) {
+		var ready bool
+		if err := r.DB().Raw(query, args...).Scan(&ready).Error; err != nil {
+			t.Fatal(err)
+		}
+		if ready {
+			return
+		}
+		time.Sleep(5 * time.Millisecond)
+	}
+	t.Fatal("database barrier was not reached")
+}
+
+func backupImportBarrier(t *testing.T, r *repo.Repository, table, timing, event, condition string) (*sql.Tx, int64) {
+	t.Helper()
+	pool, err := r.DB().DB()
+	if err != nil {
+		t.Fatal(err)
+	}
+	barrier, err := pool.Begin()
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() { _ = barrier.Rollback() })
+	key := time.Now().UnixNano() & 0x3fffffff
+	if _, err := barrier.Exec(`SELECT pg_advisory_xact_lock($1)`, key); err != nil {
+		t.Fatal(err)
+	}
+	guardEnd := ""
+	if condition != "" {
+		guardEnd = "END IF;"
+	}
+	function := fmt.Sprintf(`CREATE FUNCTION pause_backup_test() RETURNS trigger LANGUAGE plpgsql AS $$ BEGIN %s PERFORM pg_advisory_xact_lock(%d); %s RETURN NEW; END $$`, condition, key, guardEnd)
+	if err := r.DB().Exec(function).Error; err != nil {
+		t.Fatal(err)
+	}
+	trigger := fmt.Sprintf(`CREATE TRIGGER pause_backup_test %s %s ON %s FOR EACH ROW EXECUTE FUNCTION pause_backup_test()`, timing, event, table)
+	if err := r.DB().Exec(trigger).Error; err != nil {
+		t.Fatal(err)
+	}
+	return barrier, key
+}
+
+func TestPostgresBackupImportSerializesConcurrentCreatesAndImports(t *testing.T) {
+	r := ownerNamesRepository(t, "postgres")()
+	barrier, key := backupImportBarrier(t, r, "speed_limit", "BEFORE", "INSERT", "IF NEW.name = 'hold-import' THEN")
+	first := make(chan error, 1)
+	go func() {
+		_, err := r.Import(&model.BackupData{SpeedLimits: []model.SpeedLimitBackup{{ID: 100, Name: "hold-import"}}}, []string{"speedLimits"})
+		first <- err
+	}()
+	waitForBackupDBCondition(t, r, `SELECT EXISTS (SELECT 1 FROM pg_locks WHERE locktype='advisory' AND objid=? AND NOT granted)`, key)
+	created := make(chan error, 1)
+	go func() {
+		id, err := r.CreateSpeedLimit("concurrent-create", 100, 0, 1)
+		if err == nil && id <= 100 {
+			err = fmt.Errorf("reused imported ID: %d", id)
+		}
+		created <- err
+	}()
+	waitForBackupDBCondition(t, r, `SELECT EXISTS (SELECT 1 FROM pg_locks WHERE relation='speed_limit'::regclass AND NOT granted)`)
+	second := make(chan error, 1)
+	go func() {
+		result, err := r.Import(&model.BackupData{SpeedLimits: []model.SpeedLimitBackup{{ID: 200, Name: "second-import"}}}, []string{"speedLimits"})
+		if err == nil && result.SpeedLimitsImported != 1 {
+			err = fmt.Errorf("wrong retry count: %+v", result)
+		}
+		second <- err
+	}()
+	if err := barrier.Commit(); err != nil {
+		t.Fatal(err)
+	}
+	for name, done := range map[string]<-chan error{"first import": first, "create": created, "second import": second} {
+		select {
+		case err := <-done:
+			if err != nil {
+				t.Errorf("%s: %v", name, err)
+			}
+		case <-time.After(3 * time.Second):
+			t.Fatalf("%s blocked", name)
+		}
+	}
+	if id, err := r.CreateSpeedLimit("after-both", 100, 0, 1); err != nil || id <= 200 {
+		t.Fatalf("second import sequence not advanced: id=%d err=%v", id, err)
+	}
+	got, err := r.ExportAll()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(got.SpeedLimits) != 4 {
+		t.Fatalf("lost concurrent rows: %+v", got.SpeedLimits)
+	}
+}
+
+func TestPostgresBackupImportAvoidsCascadeDeleteDeadlock(t *testing.T) {
+	for _, mode := range []string{"retry-success", "busy-bounded"} {
+		t.Run(mode, func(t *testing.T) {
+			r := ownerNamesRepository(t, "postgres")()
+			user, err := r.CreateUser("delete-me", "hash", 1, 0, 0, 0, 0, 1, 0, 0)
+			if err != nil {
+				t.Fatal(err)
+			}
+			forward, err := r.CreateForwardTx(user, "delete-me", "old", 1, "127.0.0.1:80", "", 0, 0, []int64{1}, 12345, "", nil, 0, 0, nil, 0, 0, 0)
+			if err != nil {
+				t.Fatal(err)
+			}
+			// Pause a real public cascade after deleting a child row, before it
+			// reaches forward/user. Import must not retain partial parent locks.
+			barrier, key := backupImportBarrier(t, r, "forward_port", "AFTER", "DELETE", "")
+			deleted := make(chan error, 1)
+			go func() { deleted <- r.DeleteUserCascade(user) }()
+			waitForBackupDBCondition(t, r, `SELECT EXISTS (SELECT 1 FROM pg_locks WHERE locktype='advisory' AND objid=? AND NOT granted)`, key)
+			emptyPorts := []model.ForwardPortBackup{}
+			backup := &model.BackupData{
+				Users:    []model.UserBackup{{ID: 100, User: "restored", Pwd: "$2-test-fixture", RoleID: 1}},
+				Forwards: []model.ForwardBackup{{ID: forward, UserID: 100, Name: "restored", ForwardPorts: &emptyPorts}},
+			}
+			imported := make(chan error, 1)
+			runImport := func() {
+				result, err := r.Import(backup, []string{"users", "forwards"})
+				if err == nil && (result.UsersImported != 1 || result.ForwardsImported != 1) {
+					err = fmt.Errorf("wrong retry count: %+v", result)
+				}
+				imported <- err
+			}
+			go runImport()
+			if mode == "busy-bounded" {
+				select {
+				case err := <-imported:
+					if err == nil || !strings.Contains(err.Error(), "database is busy") {
+						t.Fatalf("expected bounded busy error, got %v", err)
+					}
+				case <-time.After(3 * time.Second):
+					_ = barrier.Rollback()
+					t.Fatal("import waited while holding partial table locks")
+				}
+			} else {
+				// The held child lock makes every attempt fail before writes.
+				// Let several bounded attempts encounter it before release.
+				time.Sleep(75 * time.Millisecond)
+			}
+			if err := barrier.Commit(); err != nil {
+				t.Fatal(err)
+			}
+			select {
+			case err := <-deleted:
+				if err != nil {
+					t.Fatalf("cascade: %v", err)
+				}
+			case <-time.After(3 * time.Second):
+				t.Fatal("cascade deadlocked")
+			}
+			if mode == "busy-bounded" {
+				go runImport()
+			}
+			select {
+			case err := <-imported:
+				if err != nil {
+					t.Fatalf("import: %v", err)
+				}
+			case <-time.After(3 * time.Second):
+				t.Fatal("import deadlocked")
+			}
+			if id, err := r.CreateUser("after", "hash", 1, 0, 0, 0, 0, 1, 0, 0); err != nil || id <= 100 {
+				t.Fatalf("create after concurrent cascade: id=%d err=%v", id, err)
+			}
+		})
+	}
+}
+
+func TestPostgresBackupImportRollsBackEarlierSequenceWhenLaterSequenceFails(t *testing.T) {
+	r := ownerNamesRepository(t, "postgres")()
+	if err := r.DB().Exec(`ALTER SEQUENCE speed_limit_id_seq MAXVALUE 10`).Error; err != nil {
+		t.Fatal(err)
+	}
+	backup := &model.BackupData{
+		Users:       []model.UserBackup{{ID: 100, User: "rollback-user", Pwd: "$2-test-fixture", RoleID: 1}},
+		SpeedLimits: []model.SpeedLimitBackup{{ID: 10, Name: "exhausted"}},
+	}
+	// User sequence advances first. The exhausted limit sequence then fails.
+	if _, err := r.Import(backup, []string{"users", "speedLimits"}); err == nil || !strings.Contains(err.Error(), "sequence exhausted") {
+		t.Fatalf("expected sequence exhaustion: %v", err)
+	}
+	if id, err := r.CreateUser("after-failure", "hash", 1, 0, 0, 0, 0, 1, 0, 0); err != nil || id != 2 {
+		t.Fatalf("earlier sequence failed to roll back: id=%d err=%v", id, err)
+	}
+	if id, err := r.CreateSpeedLimit("after-failure", 100, 0, 1); err != nil || id != 1 {
+		t.Fatalf("later sequence changed: id=%d err=%v", id, err)
+	}
+	got, err := r.ExportAll()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(got.Users) != 2 || len(got.SpeedLimits) != 1 {
+		t.Fatalf("partial import committed: %+v", got)
+	}
+}
+
+func TestPostgresBackupImportAPIAllowsImmediateCreate(t *testing.T) {
+	r := ownerNamesRepository(t, "postgres")()
+	const secret = "backup-sequence-contract"
+	router := httpserver.NewRouter(handler.New(r, secret), secret)
+	token, err := auth.GenerateToken(1, "admin_user", 0, secret)
+	if err != nil {
+		t.Fatal(err)
+	}
+	post := func(path, body string) {
+		t.Helper()
+		request := httptest.NewRequest(http.MethodPost, path, strings.NewReader(body))
+		request.Header.Set("Authorization", token)
+		request.Header.Set("Content-Type", "application/json")
+		response := httptest.NewRecorder()
+		router.ServeHTTP(response, request)
+		assertCode(t, response, 0)
+	}
+	post("/api/v1/backup/import", `{"version":"1.0","types":["users","speedLimits"],"users":[{"id":2,"user":"restored","pwd":"$2-test-fixture","roleId":1,"status":1}],"speedLimits":[{"id":1,"name":"restored","speed":100,"status":1}]}`)
+	post("/api/v1/user/create", `{"user":"after-import","pwd":"test-only-password","status":1}`)
+	post("/api/v1/speed-limit/create", `{"name":"after-import","speed":200}`)
+	got, err := r.ExportAll()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(got.Users) != 3 || got.Users[2].ID != 3 || len(got.SpeedLimits) != 2 || got.SpeedLimits[1].ID != 2 {
+		t.Fatalf("API create did not retain restored records: %+v", got)
+	}
+}