fix(#3109): catch httpx.HTTPStatusError in Watsonx model discovery

WatsonxIAMAuth.raise_for_status() raises httpx.HTTPStatusError on
IAM token exchange failures (401/403/5xx), which is not a subclass
of openai.APIError. This escaped the except clause in
_discover_models, propagating unwrapped instead of as
ModelDiscoveryError.

Widen the except tuple to (APIError, httpx.HTTPStatusError) so IAM
failures are wrapped consistently with other discovery errors.

Add a parametrized test case for httpx.HTTPStatusError to the
existing test_discover_models_wraps_api_error test.

Closes #3109

Author: fullsend-ai-coder[bot]

src/providers/inference/watsonx/provider.py

@@ -5,6 +5,7 @@
 import asyncio
 from typing import TYPE_CHECKING, Any, Optional
 
+import httpx
 from openai import APIError
 from pydantic_ai.embeddings import EmbeddingModel
 from pydantic_ai.embeddings.openai import OpenAIEmbeddingModel
@@ -63,7 +64,7 @@ async def _discover_models(self) -> list[DiscoveredModel]:
                 ),
                 self._list_foundation_model_functions(),
             )
-        except APIError as exc:
+        except (APIError, httpx.HTTPStatusError) as exc:
             raise ModelDiscoveryError(self.provider_id) from exc
 
         discovered: list[DiscoveredModel] = []

tests/unit/providers/inference/watsonx/test_provider.py

@@ -128,8 +128,13 @@ async def test_discover_models_keeps_chat_and_embedding_only(
             ),
             body=None,
         ),
+        httpx.HTTPStatusError(
+            "IAM token exchange failed",
+            request=httpx.Request("POST", "https://iam.cloud.ibm.com/identity/token"),
+            response=httpx.Response(401),
+        ),
     ],
-    ids=["connection-error", "authentication-error"],
+    ids=["connection-error", "authentication-error", "iam-http-status-error"],
 )
 async def test_discover_models_wraps_api_error(
     provider: WatsonxInferenceProvider,