refactor: address review feedback — public limits property, clean tests

- Drop three tests from test_retry.py that reached into private
  attributes of third-party RetryTransport (_sync_transport,
  _async_transport); the end-to-end contract is covered by the
  pool-size regression test
- Expose a public `limits` property on HttpModelClient so tests and
  diagnostic code can assert the pool configuration without walking
  private attribute chains across three libraries
- Replace two private-chain pool assertions with a single
  `client.limits.max_connections == 600` check against the new property
- Trim "inner" from the transport docstring entry (nabinchha suggestion)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Signed-off-by: Przemysław <przemekboruta@interia.pl>

Author: przemekboruta

packages/data-designer-engine/src/data_designer/engine/models/clients/adapters/http_model_client.py

@@ -83,6 +83,11 @@ def __init__(
     def concurrency_mode(self) -> ClientConcurrencyMode:
         return self._mode
 
+    @property
+    def limits(self) -> httpx.Limits:
+        """Connection pool limits derived from ``max_parallel_requests`` at construction time."""
+        return self._limits
+
     @abstractmethod
     def _build_headers(self, extra_headers: dict[str, str]) -> dict[str, str]:
         """Build provider-specific request headers."""

packages/data-designer-engine/src/data_designer/engine/models/clients/retry.py

@@ -56,7 +56,7 @@ def create_retry_transport(
             AIMD feedback loop.  When ``False`` (used by the sync engine, which has
             no salvage queue), 429 is kept in the retry list so the transport layer
             retries it transparently.
-        transport: Optional pre-configured inner transport to pass directly to
+        transport: Optional pre-configured transport to pass directly to
             ``RetryTransport``.  Pass ``httpx.HTTPTransport`` for sync clients or
             ``httpx.AsyncHTTPTransport`` for async clients — typically with a custom
             ``limits=`` — so that the connection pool is sized correctly.  When

packages/data-designer-engine/tests/engine/models/clients/test_native_http_clients.py

@@ -296,42 +296,16 @@ async def test_acompletion_lazy_initializes_async_client(
 # ---------------------------------------------------------------------------
 
 
-def test_sync_client_pool_size_respects_max_parallel_requests() -> None:
-    """Connection pool max_connections must be 2*max_parallel_requests, not the httpx default of 100."""
-    client = OpenAICompatibleClient(
-        provider_name=_OPENAI_PROVIDER,
-        endpoint=_OPENAI_ENDPOINT,
-        api_key="sk-test",
-        max_parallel_requests=300,
-        concurrency_mode=ClientConcurrencyMode.SYNC,
-    )
-    with patch(_SYNC_CLIENT_PATCH):
-        client._get_sync_client()
-
-    # Attribute chain explained:
-    #   RetryTransport._sync_transport  → the httpx.HTTPTransport we injected
-    #   HTTPTransport._pool             → the underlying httpcore.ConnectionPool
-    #   ConnectionPool._max_connections → the hard cap configured via Limits
-    # pool_max = max(32, 2 * 300) = 600
-    assert client._transport._sync_transport._pool._max_connections == 600
+def test_client_limits_respect_max_parallel_requests() -> None:
+    """Connection pool limits must reflect max_parallel_requests (regression for issue #459).
 
-
-@pytest.mark.asyncio
-async def test_async_client_pool_size_respects_max_parallel_requests() -> None:
-    """Async connection pool max_connections must be 2*max_parallel_requests, not the httpx default of 100."""
+    pool_max = max(32, 2 * max_parallel_requests) = max(32, 600) = 600
+    """
     client = OpenAICompatibleClient(
         provider_name=_OPENAI_PROVIDER,
         endpoint=_OPENAI_ENDPOINT,
         api_key="sk-test",
         max_parallel_requests=300,
-        concurrency_mode=ClientConcurrencyMode.ASYNC,
+        concurrency_mode=ClientConcurrencyMode.SYNC,
     )
-    with patch(_ASYNC_CLIENT_PATCH):
-        client._get_async_client()
-
-    # Attribute chain explained:
-    #   RetryTransport._async_transport → the httpx.AsyncHTTPTransport we injected
-    #   AsyncHTTPTransport._pool        → the underlying httpcore.AsyncConnectionPool
-    #   AsyncConnectionPool._max_connections → the hard cap configured via Limits
-    # pool_max = max(32, 2 * 300) = 600
-    assert client._transport._async_transport._pool._max_connections == 600
+    assert client.limits.max_connections == 600

packages/data-designer-engine/tests/engine/models/clients/test_retry.py

@@ -82,28 +82,3 @@ def test_create_retry_transport_default_codes_exclude_429() -> None:
     """Default retryable_status_codes do not include 429 regardless of strip flag."""
     transport = create_retry_transport(strip_rate_limit_codes=False)
     assert 429 not in transport.retry.status_forcelist
-
-
-def test_create_retry_transport_forwards_sync_transport() -> None:
-    """Provided sync transport is used directly rather than replaced with a default pool."""
-    import httpx
-
-    inner = httpx.HTTPTransport(limits=httpx.Limits(max_connections=600))
-    transport = create_retry_transport(transport=inner)
-    assert transport._sync_transport is inner
-
-
-def test_create_retry_transport_forwards_async_transport() -> None:
-    """Provided async transport is used directly rather than replaced with a default pool."""
-    import httpx
-
-    inner = httpx.AsyncHTTPTransport(limits=httpx.Limits(max_connections=600))
-    transport = create_retry_transport(transport=inner)
-    assert transport._async_transport is inner
-
-
-def test_create_retry_transport_no_transport_creates_defaults() -> None:
-    """Without a transport argument both sync and async default pools are created."""
-    transport = create_retry_transport()
-    assert transport._sync_transport is not None
-    assert transport._async_transport is not None