chore: import upstream snapshot with attribution

tests/tracing/test_set_api_key_fix.py

@@ -0,0 +1,23 @@
+import pytest
+
+from agents.tracing.processors import BackendSpanExporter
+
+
+def test_set_api_key_preserves_env_fallback(monkeypatch: pytest.MonkeyPatch):
+    """Test that set_api_key doesn't break environment variable fallback."""
+    monkeypatch.setenv("OPENAI_API_KEY", "env-key")
+
+    exporter = BackendSpanExporter()
+
+    # Initially should use env var
+    assert exporter.api_key == "env-key"
+
+    # Set explicit key
+    exporter.set_api_key("explicit-key")
+    assert exporter.api_key == "explicit-key"
+
+    # Clear explicit key and verify env fallback works
+    exporter._api_key = None
+    if "api_key" in exporter.__dict__:
+        del exporter.__dict__["api_key"]
+    assert exporter.api_key == "env-key"