diff --git a/internal/runtime/persist/persist.go b/internal/runtime/persist/persist.go
new file mode 100644
index 0000000..0fb4ef7
--- /dev/null
+++ b/internal/runtime/persist/persist.go
@@ -0,0 +1,290 @@
+// Package persist provides durable, SQLite-backed checkpoint storage for the
+// runtime agent loop.
+//
+// It implements the checkpoint (durable execution) requirement described in
+// DevDocs/design/04-运行时.md §1: the agent loop persists a Checkpoint at every
+// step so a long-running task can be interrupted and resumed later without
+// losing context.
+//
+// The store reuses the *sql.DB opened by internal/db, which already limits the
+// pool to a single connection (SetMaxOpenConns(1)) so all writes are serialized
+// and never contend on SQLite's single-writer lock. The package therefore owns
+// the checkpoints table only; it does not open or configure connections.
+//
+// Checkpoints are keyed by ID and grouped by AgentID. The full state of a step
+// is carried as JSON bytes in State, so a checkpoint record is self-contained
+// and can be restored by simply setting it back as the loop's working state.
+package persist
+
+import (
+	"context"
+	"database/sql"
+	"errors"
+	"fmt"
+	"io"
+	"log/slog"
+	"time"
+)
+
+// Package-level sentinel errors. Each is wrapped with %w at the call site so
+// callers can use errors.Is.
+var (
+	// ErrNotFound is returned when a checkpoint for the requested ID or agent
+	// does not exist.
+	ErrNotFound = errors.New("persist: checkpoint not found")
+
+	// ErrNilDB is returned when New receives a nil *sql.DB.
+	ErrNilDB = errors.New("persist: nil database handle")
+
+	// ErrMissingID is returned by Save when the checkpoint ID is blank.
+	ErrMissingID = errors.New("persist: checkpoint id is empty")
+)
+
+// Checkpoint is a single durable snapshot of the runtime agent loop state at one
+// step.
+type Checkpoint struct {
+	// ID uniquely identifies the checkpoint.
+	ID string
+	// AgentID groups checkpoints by the agent loop that produced them.
+	AgentID string
+	// Step is the loop step index this checkpoint represents.
+	Step int
+	// State is the JSON-encoded loop state at this step.
+	State []byte
+	// CreatedAt is when the checkpoint was first written. On upsert it is
+	// preserved from the original insert.
+	CreatedAt time.Time
+	// UpdatedAt is when the checkpoint was last written. Save always refreshes
+	// it to the current time.
+	UpdatedAt time.Time
+}
+
+// Store persists and queries checkpoints against a shared *sql.DB.
+//
+// A Store is safe for concurrent use; the underlying single-connection pool
+// serializes writes. The caller supplies the *sql.DB (typically from
+// internal/db.Open) and remains responsible for closing it.
+type Store struct {
+	db  *sql.DB
+	log *slog.Logger
+}
+
+// DDL for the checkpoints table. Idempotent: both statements are safe to run
+// repeatedly.
+const (
+	createTableSQL = `CREATE TABLE IF NOT EXISTS checkpoints (
+		id         TEXT PRIMARY KEY,
+		agent_id   TEXT NOT NULL,
+		step       INTEGER NOT NULL,
+		state      TEXT NOT NULL,
+		created_at TEXT NOT NULL,
+		updated_at TEXT NOT NULL
+	)`
+
+	createIndexSQL = `CREATE INDEX IF NOT EXISTS idx_checkpoints_agent_id ON checkpoints(agent_id)`
+
+	upsertSQL = `INSERT INTO checkpoints (id, agent_id, step, state, created_at, updated_at)
+		VALUES (?, ?, ?, ?, ?, ?)
+		ON CONFLICT(id) DO UPDATE SET
+			agent_id = excluded.agent_id,
+			step     = excluded.step,
+			state    = excluded.state,
+			updated_at = excluded.updated_at`
+
+	loadSQL = `SELECT id, agent_id, step, state, created_at, updated_at
+		FROM checkpoints WHERE id = ?`
+
+	loadLatestSQL = `SELECT id, agent_id, step, state, created_at, updated_at
+		FROM checkpoints WHERE agent_id = ?
+		ORDER BY updated_at DESC, step DESC LIMIT 1`
+
+	listSQL = `SELECT id, agent_id, step, state, created_at, updated_at
+		FROM checkpoints WHERE agent_id = ?
+		ORDER BY step ASC`
+
+	deleteSQL = `DELETE FROM checkpoints WHERE id = ?`
+)
+
+// New creates a Store on db and ensures the checkpoints table and its index
+// exist. It is idempotent and may be called more than once.
+//
+// db must be non-nil; it is typically the *sql.DB returned by internal/db.Open,
+// which already constrains the pool to a single connection for write
+// serialization. The caller owns db and must Close it when done. log may be nil
+// and is replaced with a discard logger so the Store can always log safely.
+func New(ctx context.Context, db *sql.DB, log *slog.Logger) (*Store, error) {
+	if db == nil {
+		return nil, fmt.Errorf("persist: new: %w", ErrNilDB)
+	}
+	log = discardLogger(log)
+
+	if _, err := db.ExecContext(ctx, createTableSQL); err != nil {
+		return nil, fmt.Errorf("persist: create table: %w", err)
+	}
+	if _, err := db.ExecContext(ctx, createIndexSQL); err != nil {
+		return nil, fmt.Errorf("persist: create index: %w", err)
+	}
+	return &Store{db: db, log: log}, nil
+}
+
+// Save upserts cp inside a transaction. For a new ID the CreatedAt is set to
+// now when cp.CreatedAt is zero; for an existing ID the original CreatedAt is
+// preserved and only the step, state and UpdatedAt are refreshed.
+func (s *Store) Save(ctx context.Context, cp *Checkpoint) error {
+	if cp == nil {
+		return fmt.Errorf("persist: save: %w", ErrNotFound)
+	}
+	if cp.ID == "" {
+		return fmt.Errorf("persist: save: %w", ErrMissingID)
+	}
+
+	now := time.Now().UTC()
+	createdAt := cp.CreatedAt
+	if createdAt.IsZero() {
+		createdAt = now
+	}
+
+	tx, err := s.db.BeginTx(ctx, nil)
+	if err != nil {
+		return fmt.Errorf("persist: save: begin: %w", err)
+	}
+	defer func() { _ = tx.Rollback() }()
+
+	if _, err := tx.ExecContext(ctx, upsertSQL,
+		cp.ID, cp.AgentID, cp.Step, string(cp.State),
+		formatTime(createdAt), formatTime(now),
+	); err != nil {
+		return fmt.Errorf("persist: save: upsert: %w", err)
+	}
+	if err := tx.Commit(); err != nil {
+		return fmt.Errorf("persist: save: commit: %w", err)
+	}
+
+	s.log.Debug("checkpoint saved", "id", cp.ID, "agent_id", cp.AgentID, "step", cp.Step)
+	return nil
+}
+
+// Load returns the checkpoint with the given id, or ErrNotFound when it does
+// not exist.
+func (s *Store) Load(ctx context.Context, id string) (*Checkpoint, error) {
+	cp, err := scanCheckpoint(s.db.QueryRowContext(ctx, loadSQL, id))
+	if errors.Is(err, sql.ErrNoRows) {
+		return nil, fmt.Errorf("persist: load(%s): %w", id, ErrNotFound)
+	}
+	if err != nil {
+		return nil, fmt.Errorf("persist: load(%s): %w", id, err)
+	}
+	return cp, nil
+}
+
+// LoadLatest returns the most recently updated checkpoint for agentID, or
+// ErrNotFound when the agent has no checkpoints.
+func (s *Store) LoadLatest(ctx context.Context, agentID string) (*Checkpoint, error) {
+	cp, err := scanCheckpoint(s.db.QueryRowContext(ctx, loadLatestSQL, agentID))
+	if errors.Is(err, sql.ErrNoRows) {
+		return nil, fmt.Errorf("persist: load_latest(%s): %w", agentID, ErrNotFound)
+	}
+	if err != nil {
+		return nil, fmt.Errorf("persist: load_latest(%s): %w", agentID, err)
+	}
+	return cp, nil
+}
+
+// List returns every checkpoint for agentID in ascending step order. It returns
+// an empty (non-nil) slice when the agent has no checkpoints.
+func (s *Store) List(ctx context.Context, agentID string) ([]Checkpoint, error) {
+	rows, err := s.db.QueryContext(ctx, listSQL, agentID)
+	if err != nil {
+		return nil, fmt.Errorf("persist: list(%s): %w", agentID, err)
+	}
+	defer func() { _ = rows.Close() }()
+
+	checkpoints := make([]Checkpoint, 0)
+	for rows.Next() {
+		cp, err := scanCheckpoint(rows)
+		if err != nil {
+			return nil, fmt.Errorf("persist: list(%s): scan: %w", agentID, err)
+		}
+		checkpoints = append(checkpoints, *cp)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, fmt.Errorf("persist: list(%s): %w", agentID, err)
+	}
+	return checkpoints, nil
+}
+
+// Delete removes the checkpoint with the given id. It returns ErrNotFound when
+// no checkpoint with that id existed.
+func (s *Store) Delete(ctx context.Context, id string) error {
+	res, err := s.db.ExecContext(ctx, deleteSQL, id)
+	if err != nil {
+		return fmt.Errorf("persist: delete(%s): %w", id, err)
+	}
+	n, err := res.RowsAffected()
+	if err != nil {
+		return fmt.Errorf("persist: delete(%s): rows affected: %w", id, err)
+	}
+	if n == 0 {
+		return fmt.Errorf("persist: delete(%s): %w", id, ErrNotFound)
+	}
+	s.log.Debug("checkpoint deleted", "id", id)
+	return nil
+}
+
+// rowScanner is the subset of *sql.Row/*sql.Rows that scanCheckpoint needs,
+// allowing it to serve both a single-row and a multi-row query.
+type rowScanner interface {
+	Scan(dest ...any) error
+}
+
+// scanCheckpoint scans one checkpoint row following the fixed column order of
+// the SELECT statements. It returns sql.ErrNoRows untouched so callers can
+// translate it to ErrNotFound.
+func scanCheckpoint(sc rowScanner) (*Checkpoint, error) {
+	var (
+		id              string
+		agentID         string
+		step            int
+		state           string
+		createdAt, upAt string
+	)
+	if err := sc.Scan(&id, &agentID, &step, &state, &createdAt, &upAt); err != nil {
+		return nil, err
+	}
+
+	createdTime, err := parseTime(createdAt)
+	if err != nil {
+		return nil, fmt.Errorf("parse created_at: %w", err)
+	}
+	updatedTime, err := parseTime(upAt)
+	if err != nil {
+		return nil, fmt.Errorf("parse updated_at: %w", err)
+	}
+	return &Checkpoint{
+		ID:        id,
+		AgentID:   agentID,
+		Step:      step,
+		State:     []byte(state),
+		CreatedAt: createdTime,
+		UpdatedAt: updatedTime,
+	}, nil
+}
+
+// formatTime renders t as a UTC RFC3339 timestamp with nanosecond precision.
+func formatTime(t time.Time) string {
+	return t.UTC().Format(time.RFC3339Nano)
+}
+
+// parseTime parses a timestamp written by formatTime.
+func parseTime(s string) (time.Time, error) {
+	return time.Parse(time.RFC3339Nano, s)
+}
+
+// discardLogger returns log if non-nil, otherwise a logger that writes nowhere,
+// so the Store can always log safely.
+func discardLogger(log *slog.Logger) *slog.Logger {
+	if log != nil {
+		return log
+	}
+	return slog.New(slog.NewTextHandler(io.Discard, nil))
+}
diff --git a/internal/runtime/persist/persist_test.go b/internal/runtime/persist/persist_test.go
new file mode 100644
index 0000000..d9755c4
--- /dev/null
+++ b/internal/runtime/persist/persist_test.go
@@ -0,0 +1,362 @@
+package persist
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"io"
+	"log/slog"
+	"sync"
+	"testing"
+	"time"
+
+	dbpkg "git.yeij.top/AskaEth/Cyrene_v2/internal/db"
+)
+
+// testLogger returns a logger that writes nowhere, keeping test output clean.
+func testLogger() *slog.Logger {
+	return slog.New(slog.NewTextHandler(io.Discard, nil))
+}
+
+// newTestStore opens an isolated in-memory SQLite database and returns a Store
+// backed by it. Each call owns a private database, so parallel tests do not
+// interfere with one another.
+func newTestStore(t *testing.T) *Store {
+	t.Helper()
+	ctx := context.Background()
+
+	db, err := dbpkg.Open(ctx, ":memory:", testLogger())
+	if err != nil {
+		t.Fatalf("open in-memory db: %v", err)
+	}
+	t.Cleanup(func() { _ = db.Close() })
+
+	s, err := New(ctx, db, testLogger())
+	if err != nil {
+		t.Fatalf("New(store) error: %v", err)
+	}
+	return s
+}
+
+func TestStore_SaveLoad_正常(t *testing.T) {
+	t.Parallel()
+	ctx := context.Background()
+	s := newTestStore(t)
+
+	cp := &Checkpoint{
+		ID:      "cp-1",
+		AgentID: "agent-a",
+		Step:    3,
+		State:   []byte(`{"turn":3,"msg":"hello"}`),
+	}
+	if err := s.Save(ctx, cp); err != nil {
+		t.Fatalf("Save error: %v", err)
+	}
+
+	got, err := s.Load(ctx, "cp-1")
+	if err != nil {
+		t.Fatalf("Load error: %v", err)
+	}
+	if got.ID != cp.ID || got.AgentID != cp.AgentID || got.Step != cp.Step {
+		t.Fatalf("round-trip mismatch: got %+v", got)
+	}
+	if string(got.State) != string(cp.State) {
+		t.Fatalf("state mismatch: got %q want %q", got.State, cp.State)
+	}
+	if got.CreatedAt.IsZero() || got.UpdatedAt.IsZero() {
+		t.Fatalf("timestamps not set: created=%v updated=%v", got.CreatedAt, got.UpdatedAt)
+	}
+}
+
+func TestStore_Load_Missing_异常(t *testing.T) {
+	t.Parallel()
+	ctx := context.Background()
+	s := newTestStore(t)
+
+	if _, err := s.Load(ctx, "does-not-exist"); !errors.Is(err, ErrNotFound) {
+		t.Fatalf("Load(missing) err = %v, want wrap of ErrNotFound", err)
+	}
+}
+
+func TestStore_LoadLatest_正常(t *testing.T) {
+	t.Parallel()
+	ctx := context.Background()
+	s := newTestStore(t)
+
+	// Save steps in ascending order; the latest save must be the newest step.
+	for step := 1; step <= 3; step++ {
+		cp := &Checkpoint{
+			ID:      fmt.Sprintf("cp-%d", step),
+			AgentID: "agent-a",
+			Step:    step,
+			State:   []byte(fmt.Sprintf(`{"step":%d}`, step)),
+		}
+		if err := s.Save(ctx, cp); err != nil {
+			t.Fatalf("Save(step %d) error: %v", step, err)
+		}
+	}
+
+	got, err := s.LoadLatest(ctx, "agent-a")
+	if err != nil {
+		t.Fatalf("LoadLatest error: %v", err)
+	}
+	if got.Step != 3 {
+		t.Fatalf("LoadLatest step = %d, want 3", got.Step)
+	}
+	if got.ID != "cp-3" {
+		t.Fatalf("LoadLatest id = %q, want cp-3", got.ID)
+	}
+}
+
+func TestStore_LoadLatest_Missing_异常(t *testing.T) {
+	t.Parallel()
+	ctx := context.Background()
+	s := newTestStore(t)
+
+	if _, err := s.LoadLatest(ctx, "no-such-agent"); !errors.Is(err, ErrNotFound) {
+		t.Fatalf("LoadLatest(missing) err = %v, want wrap of ErrNotFound", err)
+	}
+}
+
+func TestStore_List_正常(t *testing.T) {
+	t.Parallel()
+	ctx := context.Background()
+	s := newTestStore(t)
+
+	// agent-a gets steps 1 and 2; agent-b gets a single step.
+	for _, cp := range []*Checkpoint{
+		{ID: "a-1", AgentID: "agent-a", Step: 1, State: []byte(`{"step":1}`)},
+		{ID: "a-2", AgentID: "agent-a", Step: 2, State: []byte(`{"step":2}`)},
+		{ID: "b-1", AgentID: "agent-b", Step: 1, State: []byte(`{"step":1}`)},
+	} {
+		if err := s.Save(ctx, cp); err != nil {
+			t.Fatalf("Save(%s) error: %v", cp.ID, err)
+		}
+	}
+
+	listA, err := s.List(ctx, "agent-a")
+	if err != nil {
+		t.Fatalf("List(agent-a) error: %v", err)
+	}
+	if len(listA) != 2 {
+		t.Fatalf("List(agent-a) length = %d, want 2", len(listA))
+	}
+	if listA[0].Step != 1 || listA[1].Step != 2 {
+		t.Fatalf("List(agent-a) not ascending by step: %+v", listA)
+	}
+
+	listB, err := s.List(ctx, "agent-b")
+	if err != nil {
+		t.Fatalf("List(agent-b) error: %v", err)
+	}
+	if len(listB) != 1 {
+		t.Fatalf("List(agent-b) length = %d, want 1", len(listB))
+	}
+
+	// An agent with no checkpoints returns an empty, non-nil slice.
+	none, err := s.List(ctx, "no-such-agent")
+	if err != nil {
+		t.Fatalf("List(none) error: %v", err)
+	}
+	if none == nil {
+		t.Fatalf("List(none) returned nil slice, want empty non-nil")
+	}
+	if len(none) != 0 {
+		t.Fatalf("List(none) length = %d, want 0", len(none))
+	}
+}
+
+func TestStore_Save_Upsert_正常(t *testing.T) {
+	t.Parallel()
+	ctx := context.Background()
+	s := newTestStore(t)
+
+	// A clearly past timestamp: the store must preserve it across the upsert
+	// while refreshing UpdatedAt to the current time.
+	originalCreated := time.Date(2024, time.January, 1, 0, 0, 0, 0, time.UTC)
+	first := &Checkpoint{
+		ID:        "cp-1",
+		AgentID:   "agent-a",
+		Step:      1,
+		State:     []byte(`{"step":1}`),
+		CreatedAt: originalCreated,
+	}
+	if err := s.Save(ctx, first); err != nil {
+		t.Fatalf("Save(first) error: %v", err)
+	}
+
+	// A second save with the same ID must keep the original CreatedAt while
+	// refreshing step, state and UpdatedAt.
+	second := &Checkpoint{
+		ID:      "cp-1",
+		AgentID: "agent-a",
+		Step:    2,
+		State:   []byte(`{"step":2}`),
+	}
+	if err := s.Save(ctx, second); err != nil {
+		t.Fatalf("Save(second) error: %v", err)
+	}
+
+	got, err := s.Load(ctx, "cp-1")
+	if err != nil {
+		t.Fatalf("Load error: %v", err)
+	}
+	if got.Step != 2 {
+		t.Fatalf("upsert step = %d, want 2", got.Step)
+	}
+	if string(got.State) != `{"step":2}` {
+		t.Fatalf("upsert state = %q, want step 2", got.State)
+	}
+	if !got.CreatedAt.Equal(originalCreated) {
+		t.Fatalf("upsert created_at = %v, want preserved %v", got.CreatedAt, originalCreated)
+	}
+	if got.UpdatedAt.Before(got.CreatedAt) {
+		t.Fatalf("upsert updated_at %v is before created_at %v", got.UpdatedAt, got.CreatedAt)
+	}
+
+	// Only one row must remain for the ID after the upsert.
+	all, err := s.List(ctx, "agent-a")
+	if err != nil {
+		t.Fatalf("List(after upsert) error: %v", err)
+	}
+	if len(all) != 1 {
+		t.Fatalf("upsert left %d rows, want 1", len(all))
+	}
+}
+
+func TestStore_Delete_正常(t *testing.T) {
+	t.Parallel()
+	ctx := context.Background()
+	s := newTestStore(t)
+
+	cp := &Checkpoint{ID: "cp-1", AgentID: "agent-a", Step: 1, State: []byte(`{}`)}
+	if err := s.Save(ctx, cp); err != nil {
+		t.Fatalf("Save error: %v", err)
+	}
+	if err := s.Delete(ctx, "cp-1"); err != nil {
+		t.Fatalf("Delete error: %v", err)
+	}
+	if _, err := s.Load(ctx, "cp-1"); !errors.Is(err, ErrNotFound) {
+		t.Fatalf("Load after delete err = %v, want ErrNotFound", err)
+	}
+}
+
+func TestStore_Delete_Missing_异常(t *testing.T) {
+	t.Parallel()
+	ctx := context.Background()
+	s := newTestStore(t)
+
+	if err := s.Delete(ctx, "never-existed"); !errors.Is(err, ErrNotFound) {
+		t.Fatalf("Delete(missing) err = %v, want wrap of ErrNotFound", err)
+	}
+}
+
+func TestStore_Save_SQLInjection_安全(t *testing.T) {
+	t.Parallel()
+	ctx := context.Background()
+	s := newTestStore(t)
+
+	// Malicious strings must be treated as opaque data, never executed as SQL.
+	cp := &Checkpoint{
+		ID:      "1'; DROP TABLE checkpoints;--",
+		AgentID: "agent'; DELETE FROM checkpoints;--",
+		Step:    1,
+		State:   []byte(`{"x":"'); DROP TABLE checkpoints;--"}`),
+	}
+	if err := s.Save(ctx, cp); err != nil {
+		t.Fatalf("Save(injection) error: %v", err)
+	}
+
+	got, err := s.Load(ctx, cp.ID)
+	if err != nil {
+		t.Fatalf("Load(injection id) error: %v", err)
+	}
+	if got.ID != cp.ID || got.AgentID != cp.AgentID {
+		t.Fatalf("injection round-trip mismatch: got %+v", got)
+	}
+	if string(got.State) != string(cp.State) {
+		t.Fatalf("injection state mismatch: got %q", got.State)
+	}
+
+	// The table must still exist and hold exactly the injected row.
+	var tableCount int
+	if err := s.db.QueryRowContext(ctx,
+		"SELECT count(*) FROM sqlite_master WHERE type='table' AND name='checkpoints'").Scan(&tableCount); err != nil {
+		t.Fatalf("query sqlite_master: %v", err)
+	}
+	if tableCount != 1 {
+		t.Fatalf("checkpoints table missing after injection, count=%d", tableCount)
+	}
+	var rowCount int
+	if err := s.db.QueryRowContext(ctx, "SELECT count(*) FROM checkpoints").Scan(&rowCount); err != nil {
+		t.Fatalf("count checkpoints: %v", err)
+	}
+	if rowCount != 1 {
+		t.Fatalf("checkpoints row count = %d, want 1", rowCount)
+	}
+}
+
+func TestStore_SaveConcurrent_并发(t *testing.T) {
+	t.Parallel()
+	ctx := context.Background()
+	s := newTestStore(t)
+
+	const agents = 8
+	const perAgent = 5
+
+	var wg sync.WaitGroup
+	errCh := make(chan error, agents*perAgent)
+	for a := 0; a < agents; a++ {
+		agentID := fmt.Sprintf("agent-%d", a)
+		for step := 0; step < perAgent; step++ {
+			wg.Add(1)
+			go func(id string, st int) {
+				defer wg.Done()
+				cp := &Checkpoint{
+					ID:      fmt.Sprintf("cp-%s-%d", id, st),
+					AgentID: id,
+					Step:    st,
+					State:   []byte(fmt.Sprintf(`{"agent":%q,"step":%d}`, id, st)),
+				}
+				if err := s.Save(ctx, cp); err != nil {
+					errCh <- err
+				}
+			}(agentID, step)
+		}
+	}
+	wg.Wait()
+	close(errCh)
+	for err := range errCh {
+		t.Fatalf("concurrent save failed: %v", err)
+	}
+
+	for a := 0; a < agents; a++ {
+		agentID := fmt.Sprintf("agent-%d", a)
+		all, err := s.List(ctx, agentID)
+		if err != nil {
+			t.Fatalf("List(%s) error: %v", agentID, err)
+		}
+		if len(all) != perAgent {
+			t.Fatalf("List(%s) length = %d, want %d", agentID, len(all), perAgent)
+		}
+	}
+}
+
+func TestStore_New_NilDB_异常(t *testing.T) {
+	t.Parallel()
+	ctx := context.Background()
+
+	if _, err := New(ctx, nil, testLogger()); !errors.Is(err, ErrNilDB) {
+		t.Fatalf("New(nil db) err = %v, want wrap of ErrNilDB", err)
+	}
+}
+
+func TestStore_Save_MissingID_异常(t *testing.T) {
+	t.Parallel()
+	ctx := context.Background()
+	s := newTestStore(t)
+
+	if err := s.Save(ctx, &Checkpoint{AgentID: "a", Step: 1, State: []byte(`{}`)}); !errors.Is(err, ErrMissingID) {
+		t.Fatalf("Save(blank id) err = %v, want wrap of ErrMissingID", err)
+	}
+}