Status line context usage does not update immediately after /compact

Current behavior

After running /compact, the status line still shows the old context
percentage (e.g., 85%) until the next assistant response is received.
Only then does it update to the new lower value (e.g., 19%).

Expected behavior

The status line should update immediately when /compact finishes,
before the next message is sent. This way the user can see the result
of the compact operation right away.

Optional improvement

As a secondary request: show an estimated post-compact context size
before running /compact (e.g., "~ 15-20% estimated"). This is harder
to implement because the summary length is not known in advance, but
even a rough estimate would be useful.

Why this matters

After a long session, the user runs /compact specifically to free up
context. Not seeing the result immediately makes it harder to know
whether there is enough room to continue or whether another compact
is needed.