Is it possible to simplify the SQL query?

Question

SQL

Good afternoon.
There is such a table of user visits to pages:

happened_at 
page 
user_id

You need to extract sessions from it in the form: user_id, session_start, session_end. Session - a sequence of user visits, less than an hour between two consecutive visits. It starts with the first one and ends an hour after the last one.
I wrote a query, but it seems to me too complicated - with two subqueries. Can it be simplified somehow?

with t as(select user_id,page,happened_at,
happened_at - lag (happened_at) over (partition by user_id order by happened_at) is null or
happened_at - lag (happened_at) over (partition by user_id order by happened_at) > interval '1 hour' as is_session_start,
lead (happened_at) over (partition by user_id order by happened_at) - happened_at is null or 
lead (happened_at) over (partition by user_id order by happened_at) - happened_at > interval '1 hour' as is_session_end 
from test.vimbox_pages ),

tt as (select user_id,page,happened_at,is_session_start,is_session_end,
coalesce(lag (happened_at) over (partition by user_id order by happened_at), happened_at) as session_start
from t 
where is_session_start=true or is_session_end=true)

select 
user_id,
session_start,
happened_at as session_end
from tt
where is_session_end=true 
order by user_id, session_start

Answer 1

it is possible if you add the session_id entry to the table initially

Answer 2

Can you explain the solution in more detail?
And if it's not difficult, then write to me in telegram @ilya8960