What
When Claude fetches a web page, a subagent can do the work. A subagent is a helper copy of Claude given one job. Its instructions now say that when a fetch fails for good, the report must say that sending the URL again would fail the same way. Before, the instructions ended by telling it to report so the caller could fetch a denied URL itself.
The check that decides whether to fetch a page ahead of time now sees the full set of permission settings and has one more case where it skips the fetch.
Why
Claude is less likely to keep retrying a URL that cannot work.