Fix test_authorization_with_existing_meta to actually test _meta merging

The previous test only verified authorization injection but did not
pre-populate any _meta fields, making it indistinguishable from
test_authorization_injected_in_meta.

Now the test constructs a RequestParams with a pre-existing progressToken
in _meta, then asserts that both progressToken and authorization are
present after _send_request serialises the params - verifying that
authorization is merged rather than replacing any existing _meta content.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: mchades

tests/test_client_session.py

@@ -20,6 +20,7 @@
 
 from adp_sdk.client import ClientSession
 from adp_sdk.client.session import basic_auth
+from adp_sdk.types.jsonrpc import RequestMeta, RequestParams
 from adp_sdk.shared import (
     ADPError,
     InvalidParamsError,
@@ -509,13 +510,18 @@ async def test_no_authorization_by_default(self) -> None:
             self.assertNotIn("authorization", meta)
 
     async def test_authorization_with_existing_meta(self) -> None:
-        """Authorization is merged with existing _meta fields."""
-        transport = _MockTransport([_make_init_response(), _make_discover_response()])
+        """Authorization is merged with existing _meta fields without overwriting them."""
+        from adp_sdk.types.jsonrpc import EmptyResult
+
+        transport = _MockTransport([_make_init_response(), _make_ping_response()])
         async with ClientSession(transport, authorization="Basic dGVzdDo=") as session:
-            await session.discover()
+            params = RequestParams(meta=RequestMeta(progress_token=42))
+            await session._send_request("adp.ping", params, EmptyResult)
 
             data = json.loads(transport.written[1])
-            self.assertEqual(data["params"]["_meta"]["authorization"], "Basic dGVzdDo=")
+            meta = data["params"]["_meta"]
+            self.assertEqual(meta["authorization"], "Basic dGVzdDo=")
+            self.assertEqual(meta["progressToken"], 42)
 
 
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