fix: replace assert with RuntimeError and fix return type annotation

- a2a_protocol/main.py: replace bare assert with descriptive RuntimeError
  in _execute_a2a_send_with_retry so retry exhaustion gives a clear message
- fine_tuning/main.py: fix _resolve_fine_tuning_timeout return type from
  float to Union[float, httpx.Timeout] to accurately reflect the passthrough path

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

litellm/a2a_protocol/main.py

@@ -198,7 +198,10 @@ async def _execute_a2a_send_with_retry(
                 continue
             except Exception:
                 raise
-    assert a2a_response is not None
+    if a2a_response is None:
+        raise RuntimeError(
+            "A2A send_message failed: no response received after retry attempts."
+        )
     return a2a_response
 
 

litellm/fine_tuning/main.py

@@ -129,13 +129,13 @@ async def acreate_fine_tuning_job(
 def _resolve_fine_tuning_timeout(
     timeout: Any,
     custom_llm_provider: str,
-) -> float:
+) -> Union[float, httpx.Timeout]:
     """Normalise a raw timeout value to a float (seconds) for fine-tuning calls."""
     timeout = timeout or 600.0
     if isinstance(timeout, httpx.Timeout):
         if not supports_httpx_timeout(custom_llm_provider):
             return float(timeout.read or 600)
-        return timeout  # type: ignore[return-value]
+        return timeout
     return float(timeout)