test(backend): add E2E harness foundation (entrypoints, middleware, LLM/embedding fakes)

surfsense_backend/tests/e2e/middleware/scenario.py

@@ -0,0 +1,54 @@
+"""X-E2E-Scenario middleware.
+
+Reads the X-E2E-Scenario request header and pipes the value into a
+ContextVar that the strict fakes consult to switch between happy-path
+and error scenarios on a per-request basis.
+
+Mounted by tests/e2e/run_backend.py only. Production never adds this
+middleware, so production never reads the header.
+
+Supported scenarios:
+- "happy" (default): everything succeeds with deterministic fixtures.
+- "denied": Composio.connected_accounts.initiate returns a redirect URL
+  pointing at our callback with ?error=access_denied.
+- "auth_expired": GOOGLEDRIVE_LIST_FILES returns an authentication
+  failure that the route translates to connector.config.auth_expired.
+- "duplicate": no special fake behavior; the duplicate path is exercised
+  by running the OAuth flow twice with the same toolkit.
+"""
+
+from __future__ import annotations
+
+from contextvars import ContextVar
+
+from starlette.middleware.base import BaseHTTPMiddleware
+from starlette.requests import Request
+from starlette.responses import Response
+from starlette.types import ASGIApp
+
+_scenario: ContextVar[str] = ContextVar("e2e_scenario", default="happy")
+
+
+def current_scenario() -> str:
+    """Return the active E2E scenario for the current request context."""
+    return _scenario.get()
+
+
+class ScenarioMiddleware(BaseHTTPMiddleware):
+    """Reads X-E2E-Scenario and exposes it via a ContextVar.
+
+    The header is also forwarded as state on the request so route
+    handlers can branch if they ever need to (Composio routes do not).
+    """
+
+    def __init__(self, app: ASGIApp) -> None:
+        super().__init__(app)
+
+    async def dispatch(self, request: Request, call_next) -> Response:
+        value = request.headers.get("X-E2E-Scenario", "happy")
+        token = _scenario.set(value)
+        try:
+            request.state.e2e_scenario = value
+            return await call_next(request)
+        finally:
+            _scenario.reset(token)