refactor(e2e): unify RouterInstance into Gateway class, split conftest.py into modular fixtures (#16671)

sgl-model-gateway/e2e_test/fixtures/__init__.py

@@ -1 +1,47 @@
-"""Shared fixtures for router integration tests."""
+"""Fixtures for E2E tests.
+
+This package contains modular pytest fixtures split by responsibility:
+- hooks.py: Pytest collection hooks and marker registration
+- pool.py: Model pool fixtures (session-scoped worker management)
+- setup_backend.py: Backend setup fixtures (class/function-scoped)
+- markers.py: Helper utilities for marker extraction
+
+Legacy modules (to be removed during e2e_response_api migration):
+- ports.py: Use infra.get_open_port() instead
+- router_manager.py: Use infra.Gateway instead
+"""
+
+# Pytest hooks (imported by conftest.py via pytest_plugins)
+from .hooks import (
+    get_pool_requirements,
+    pytest_collection_finish,
+    pytest_collection_modifyitems,
+    pytest_configure,
+    validate_gpu_requirements,
+)
+
+# Marker helpers
+from .markers import get_marker_kwargs, get_marker_value
+
+# Fixtures (imported by conftest.py)
+from .pool import model_base_url, model_client, model_pool
+from .setup_backend import backend_router, setup_backend
+
+__all__ = [
+    # Hooks
+    "pytest_collection_modifyitems",
+    "pytest_collection_finish",
+    "pytest_configure",
+    "get_pool_requirements",
+    "validate_gpu_requirements",
+    # Pool fixtures
+    "model_pool",
+    "model_client",
+    "model_base_url",
+    # Backend fixtures
+    "setup_backend",
+    "backend_router",
+    # Marker helpers
+    "get_marker_value",
+    "get_marker_kwargs",
+]