diff --git a/credential_crypto.py b/credential_crypto.py
index 9e31f2e..d1813b6 100644
--- a/credential_crypto.py
+++ b/credential_crypto.py
@@ -132,9 +132,8 @@ def encrypt_secret(value: str | None, db_path: Path) -> str:
     if not value or is_encrypted(value):
         return value or ""
     raw = value.encode("utf-8")
-    if os.name == "nt" and not os.environ.get("CB_GATEWAY_MASTER_KEY"):
-        protected = _dpapi_encrypt(raw)
-        return _DPAPI_PREFIX + base64.urlsafe_b64encode(protected).decode("ascii")
+    # Always Fernet (MASTER_KEY or sidecar key file). Linux Docker cannot open
+    # Windows DPAPI rows; existing enc:v1:dpapi: values still decrypt on Windows.
     token = _get_fernet(db_path).encrypt(raw).decode("ascii")
     return _FERNET_PREFIX + token
 
diff --git a/docker-compose.yml b/docker-compose.yml
index ed5ddc5..448430f 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -20,8 +20,9 @@ services:
       - CB_AUTH_DIR=/auth
       - CB_CONTAINER_AUTH_DIR=/auth
       - CB_DOCKER=1
-      # Topology: Windows host + Linux container cannot decrypt DPAPI blobs.
-      # Set CB_GATEWAY_MASTER_KEY when the SQLite file is shared across OS.
+      # Official QClaw/QwenWork login files are Windows DPAPI; import them on
+      # the host. SQLite tokens use the sidecar key file (or MASTER_KEY) so
+      # Linux can use already-imported accounts. WorkBuddy still mounts /auth.
     healthcheck:
       test: ["CMD", "python", "-c", "import urllib.request; urllib.request.urlopen('http://127.0.0.1:8787/health', timeout=3)"]
       interval: 30s
diff --git a/tests/test_core.py b/tests/test_core.py
index ab4c81e..f3475b6 100644
--- a/tests/test_core.py
+++ b/tests/test_core.py
@@ -300,6 +300,21 @@ def isolated_db(tmp_path, monkeypatch):
     credential_crypto.reset_cache()
 
 
+def test_encrypt_without_master_key_uses_fernet_key_file(tmp_path, monkeypatch):
+    path = tmp_path / "gateway.db"
+    monkeypatch.setattr(db, "DB_PATH", path)
+    monkeypatch.delenv("CB_GATEWAY_MASTER_KEY", raising=False)
+    credential_crypto.reset_cache()
+    db.init_db()
+    account_id = db.add_account({"name": "portable", "access_token": "access-secret"})
+    with sqlite3.connect(path) as conn:
+        raw = conn.execute("SELECT access_token FROM accounts WHERE id=?", (account_id,)).fetchone()[0]
+    assert raw.startswith("enc:v1:fernet:")
+    assert "access-secret" not in raw
+    assert db.get_account(account_id)["access_token"] == "access-secret"
+    credential_crypto.reset_cache()
+
+
 def test_account_credentials_are_encrypted_at_rest(isolated_db):
     account_id = db.add_account(
         {