Fix double URL-encoding of context param in remote feature flags

The `_prepare_query_params` method was manually URL-encoding the JSON
context string via `urllib.parse.quote()` before passing it as an httpx
query parameter. Since httpx also URL-encodes all query parameter values,
the context was double-encoded — e.g. `{` became `%257B` instead of
`%7B` — causing the Mixpanel `/flags` API to return 400 Bad Request.

The fix passes the raw JSON string directly and lets httpx handle the
single layer of URL encoding as intended.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: corleymj

mixpanel/flags/remote_feature_flags.py

@@ -3,7 +3,6 @@
 import asyncio
 import json
 import logging
-import urllib.parse
 from datetime import datetime
 from typing import Any, Callable
 
@@ -277,9 +276,7 @@ def _prepare_query_params(
         self, context: dict[str, Any], flag_key: str | None = None
     ) -> dict[str, str]:
         params = self._request_params_base.copy()
-        context_json = json.dumps(context).encode("utf-8")
-        url_encoded_context = urllib.parse.quote(context_json)
-        params["context"] = url_encoded_context
+        params["context"] = json.dumps(context)
         if flag_key is not None:
             params["flag_key"] = flag_key
         return params

mixpanel/flags/test_remote_feature_flags.py

@@ -201,6 +201,48 @@ async def test_atrack_exposure_event_successfully_tracks(self):
         self.mock_tracker.assert_called_once()
 
 
+class TestPrepareQueryParams:
+    def setup_method(self):
+        config = RemoteFlagsConfig()
+        self.mock_tracker = Mock()
+        self._flags = RemoteFeatureFlagsProvider(
+            "test-token", config, "1.0.0", self.mock_tracker
+        )
+
+    def teardown_method(self):
+        self._flags.__exit__(None, None, None)
+
+    def test_context_is_json_string_not_url_encoded(self):
+        context = {"distinct_id": "user123", "plan": "premium"}
+        params = self._flags._prepare_query_params(context)
+        assert params["context"] == '{"distinct_id": "user123", "plan": "premium"}'
+
+    def test_context_is_not_bytes(self):
+        context = {"distinct_id": "user123"}
+        params = self._flags._prepare_query_params(context)
+        assert isinstance(params["context"], str)
+
+    def test_flag_key_included_when_provided(self):
+        context = {"distinct_id": "user123"}
+        params = self._flags._prepare_query_params(context, flag_key="my_flag")
+        assert params["flag_key"] == "my_flag"
+
+    def test_flag_key_absent_when_not_provided(self):
+        context = {"distinct_id": "user123"}
+        params = self._flags._prepare_query_params(context)
+        assert "flag_key" not in params
+
+    @respx.mock
+    def test_request_url_has_properly_encoded_context(self):
+        respx.get(ENDPOINT).mock(return_value=create_success_response({}))
+        self._flags.get_all_variants({"distinct_id": "user123"})
+
+        request = respx.calls.last.request
+        url_str = str(request.url)
+        assert "%257B" not in url_str, "context param is double-encoded"
+        assert "b%27" not in url_str, "context param contains bytes literal"
+
+
 class TestRemoteFeatureFlagsProviderSync:
     def setup_method(self):
         config = RemoteFlagsConfig()