I'd rather not name postgres_fdw explicitly, or at least not solely, as a reason for setting this to zero. Additionally, using postgres_fdw within the server doesn't cause issues, its using postgres_fdw and the remote server having this setting set to zero that causes a problem.
<note>
Consider setting this for specific users instead of as a server default. Client connections managed by connection poolers, or initiated indirectly like those by a remote postgres_fdw using server, should probably be excluded from this timeout.
Text within <para> should be indented one space (you missed both under listitem).
I'd suggest a comment that aside from a bit of resource consumption idle sessions do not interfere with the long-running stability of the server, unlike idle-in-transaction sessions which are controlled by the other configuration setting.
