diff --git a/internal/config/config_test.go b/internal/config/config_test.go
index f5a8d90..e47c954 100644
--- a/internal/config/config_test.go
+++ b/internal/config/config_test.go
@@ -79,6 +79,51 @@ func TestLoadStorePreservesFileBackedTokensForRuntime(t *testing.T) {
 	}
 }
 
+func TestEnvBackedStoreWritebackBootstrapsMissingConfigFile(t *testing.T) {
+	tmp, err := os.CreateTemp(t.TempDir(), "config-*.json")
+	if err != nil {
+		t.Fatalf("create temp config: %v", err)
+	}
+	path := tmp.Name()
+	_ = tmp.Close()
+	_ = os.Remove(path)
+
+	t.Setenv("DS2API_CONFIG_JSON", `{"keys":["k1"],"accounts":[{"email":"seed@example.com","password":"p"}]}`)
+	t.Setenv("CONFIG_JSON", "")
+	t.Setenv("DS2API_CONFIG_PATH", path)
+	t.Setenv("DS2API_ENV_WRITEBACK", "1")
+
+	store := LoadStore()
+	if store.IsEnvBacked() {
+		t.Fatalf("expected writeback bootstrap to become file-backed immediately")
+	}
+	if err := store.Update(func(c *Config) error {
+		c.Accounts = append(c.Accounts, Account{Email: "new@example.com", Password: "p2"})
+		return nil
+	}); err != nil {
+		t.Fatalf("update failed: %v", err)
+	}
+	content, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatalf("read written config: %v", err)
+	}
+	if !strings.Contains(string(content), "seed@example.com") {
+		t.Fatalf("expected bootstrapped config to contain seed account, got: %s", content)
+	}
+	if !strings.Contains(string(content), "new@example.com") {
+		t.Fatalf("expected persisted config to contain added account, got: %s", content)
+	}
+
+	reloaded := LoadStore()
+	if reloaded.IsEnvBacked() {
+		t.Fatalf("expected reloaded store to prefer persisted config file")
+	}
+	accounts := reloaded.Accounts()
+	if len(accounts) != 2 {
+		t.Fatalf("expected 2 accounts after reload, got %d", len(accounts))
+	}
+}
+
 func TestRuntimeTokenRefreshIntervalHoursDefaultsToSix(t *testing.T) {
 	t.Setenv("DS2API_CONFIG_JSON", `{
 		"keys":["k1"],
diff --git a/internal/config/store.go b/internal/config/store.go
index d212594..678390a 100644
--- a/internal/config/store.go
+++ b/internal/config/store.go
@@ -4,12 +4,19 @@ import (
 	"encoding/base64"
 	"encoding/json"
 	"errors"
+	"fmt"
 	"os"
+	"path/filepath"
 	"slices"
 	"strings"
 	"sync"
 )
 
+func envWritebackEnabled() bool {
+	v := strings.ToLower(strings.TrimSpace(os.Getenv("DS2API_ENV_WRITEBACK")))
+	return v == "1" || v == "true" || v == "yes" || v == "on"
+}
+
 type Store struct {
 	mu      sync.RWMutex
 	cfg     Config
@@ -42,6 +49,24 @@ func loadConfig() (Config, bool, error) {
 		cfg, err := parseConfigString(rawCfg)
 		cfg.ClearAccountTokens()
 		cfg.DropInvalidAccounts()
+		if IsVercel() || !envWritebackEnabled() {
+			return cfg, true, err
+		}
+		content, fileErr := os.ReadFile(ConfigPath())
+		if fileErr == nil {
+			var fileCfg Config
+			if unmarshalErr := json.Unmarshal(content, &fileCfg); unmarshalErr == nil {
+				fileCfg.DropInvalidAccounts()
+				return fileCfg, false, err
+			}
+		}
+		if errors.Is(fileErr, os.ErrNotExist) {
+			if writeErr := writeConfigFile(ConfigPath(), cfg.Clone()); writeErr == nil {
+				return cfg, false, err
+			} else {
+				Logger.Warn("[config] env writeback bootstrap failed", "error", writeErr)
+			}
+		}
 		return cfg, true, err
 	}
 
@@ -177,7 +202,7 @@ func (s *Store) Update(mutator func(*Config) error) error {
 func (s *Store) Save() error {
 	s.mu.Lock()
 	defer s.mu.Unlock()
-	if s.fromEnv {
+	if s.fromEnv && (IsVercel() || !envWritebackEnabled()) {
 		Logger.Info("[save_config] source from env, skip write")
 		return nil
 	}
@@ -187,11 +212,15 @@ func (s *Store) Save() error {
 	if err != nil {
 		return err
 	}
-	return os.WriteFile(s.path, b, 0o644)
+	if err := writeConfigBytes(s.path, b); err != nil {
+		return err
+	}
+	s.fromEnv = false
+	return nil
 }
 
 func (s *Store) saveLocked() error {
-	if s.fromEnv {
+	if s.fromEnv && (IsVercel() || !envWritebackEnabled()) {
 		Logger.Info("[save_config] source from env, skip write")
 		return nil
 	}
@@ -201,7 +230,32 @@ func (s *Store) saveLocked() error {
 	if err != nil {
 		return err
 	}
-	return os.WriteFile(s.path, b, 0o644)
+	if err := writeConfigBytes(s.path, b); err != nil {
+		return err
+	}
+	s.fromEnv = false
+	return nil
+}
+
+func writeConfigFile(path string, cfg Config) error {
+	persistCfg := cfg.Clone()
+	persistCfg.ClearAccountTokens()
+	b, err := json.MarshalIndent(persistCfg, "", "  ")
+	if err != nil {
+		return err
+	}
+	return writeConfigBytes(path, b)
+}
+
+func writeConfigBytes(path string, b []byte) error {
+	dir := filepath.Dir(path)
+	if dir == "." || dir == "" {
+		return os.WriteFile(path, b, 0o644)
+	}
+	if err := os.MkdirAll(dir, 0o755); err != nil {
+		return fmt.Errorf("mkdir config dir: %w", err)
+	}
+	return os.WriteFile(path, b, 0o644)
 }
 
 func (s *Store) IsEnvBacked() bool {