Add async coverage for env-header precedence behavior

Co-authored-by: Shri Sukhani <shrisukhani@users.noreply.github.com>

Author: cursoragent

tests/test_custom_headers.py

@@ -212,6 +212,39 @@ def test_client_constructor_with_config_ignores_invalid_env_headers(monkeypatch)
         client.close()
 
 
+def test_async_client_constructor_with_explicit_headers_ignores_invalid_env_headers(
+    monkeypatch,
+):
+    monkeypatch.setenv("HYPERBROWSER_HEADERS", "{invalid")
+
+    async def run() -> None:
+        client = AsyncHyperbrowser(
+            api_key="test-key",
+            headers={"X-Team-Trace": "constructor-value"},
+        )
+        try:
+            assert (
+                client.transport.client.headers["X-Team-Trace"] == "constructor-value"
+            )
+        finally:
+            await client.close()
+
+    asyncio.run(run())
+
+
+def test_async_client_constructor_with_config_ignores_invalid_env_headers(monkeypatch):
+    monkeypatch.setenv("HYPERBROWSER_HEADERS", "{invalid")
+
+    async def run() -> None:
+        client = AsyncHyperbrowser(config=ClientConfig(api_key="test-key"))
+        try:
+            assert client.transport.client.headers["x-api-key"] == "test-key"
+        finally:
+            await client.close()
+
+    asyncio.run(run())
+
+
 def test_client_constructor_headers_override_environment_headers(monkeypatch):
     monkeypatch.setenv("HYPERBROWSER_HEADERS", '{"X-Team-Trace":"env-value"}')
     client = Hyperbrowser(