Add detailed error info to auth failure messages.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

core/anthropic/errors.py

@@ -29,9 +29,11 @@ def get_user_facing_error_message(
     if isinstance(e, openai.RateLimitError):
         return "Provider rate limit reached. Please retry shortly."
     if isinstance(e, openai.AuthenticationError):
-        return "Provider authentication failed. Check API key."
+        raw = str(e)
+        return f"Provider authentication failed. Check API key. Details: {raw[:100]}"
     if isinstance(e, openai.BadRequestError):
-        return "Invalid request sent to provider."
+        raw = str(e)
+        return f"Invalid request sent to provider. Details: {raw[:100]}"
 
     name = type(e).__name__
     status_code = getattr(e, "status_code", None)