fix: align auth-disabled mode and mock history loading (#3471)

* fix: align auth-disabled mode and mock history loading

* fix: address auth-disabled review feedback

* test: cover auth-disabled backend contract

* style: format frontend tests

* fix: address follow-up review comments

backend/app/gateway/auth_disabled.py

@@ -0,0 +1,54 @@
+"""Shared helpers for local/E2E auth-disabled mode."""
+
+from __future__ import annotations
+
+import logging
+import os
+from types import SimpleNamespace
+
+AUTH_DISABLED_ENV_VAR = "DEER_FLOW_AUTH_DISABLED"
+AUTH_DISABLED_USER_ID = "e2e-user"
+AUTH_DISABLED_USER_EMAIL = "e2e@test.local"
+
+AUTH_SOURCE_SESSION = "session"
+AUTH_SOURCE_INTERNAL = "internal"
+AUTH_SOURCE_AUTH_DISABLED = "auth_disabled"
+
+_PRODUCTION_ENV_VARS: tuple[str, ...] = ("DEER_FLOW_ENV", "ENVIRONMENT")
+_PRODUCTION_ENV_VALUES: frozenset[str] = frozenset({"prod", "production"})
+
+logger = logging.getLogger(__name__)
+
+
+def is_explicit_production_environment() -> bool:
+    return any(os.environ.get(name, "").strip().lower() in _PRODUCTION_ENV_VALUES for name in _PRODUCTION_ENV_VARS)
+
+
+def is_auth_disabled_requested() -> bool:
+    return os.environ.get(AUTH_DISABLED_ENV_VAR) == "1"
+
+
+def is_auth_disabled() -> bool:
+    return is_auth_disabled_requested() and not is_explicit_production_environment()
+
+
+def warn_if_auth_disabled_enabled() -> None:
+    if not is_auth_disabled():
+        return
+
+    logger.warning(
+        "%s=1 is active: authentication is bypassed and anonymous requests run as synthetic admin user %r. Do not enable this in shared or production deployments.",
+        AUTH_DISABLED_ENV_VAR,
+        AUTH_DISABLED_USER_ID,
+    )
+
+
+def get_auth_disabled_user():
+    return SimpleNamespace(
+        id=AUTH_DISABLED_USER_ID,
+        email=AUTH_DISABLED_USER_EMAIL,
+        password_hash=None,
+        system_role="admin",
+        needs_setup=False,
+        token_version=0,
+    )