With no frontend attached, a detached session's messages go after MessageLinger

A message lingers until input dismisses it, and a detached session with nobody
attached has no input: its messages, and /screen, kept what was said long ago.
The session now marks the core unattended while no client is attached, and
the core drops a pane's messages once the newest has been up MessageLinger on
the clock, checked as it is stepped or served. A pane's older lines go with
its newest rather than each on its own clock; the render pipeline's clock is
the place for that.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

1 files changed, 2 insertions, 0 deletions

diff --git a/src/detached/server.zig b/src/detached/server.zig
index b088d833..6a4b5001 100644
--- a/src/detached/server.zig
+++ b/src/detached/server.zig
@@ -770,6 +770,8 @@ pub const Session = struct {
         const completed = s.ninep_wake.swap(false, .acq_rel) or drained;
         for (&s.clients) |*c| if (c.fd >= 0) s.flush(c);
         const regridded = s.reconcile();
+        // Nobody attached, nobody to dismiss a message (expireUnattended).
+        s.core.unattended = s.primary() == null;
 
         const now = monotonicMs();
         var fds: [poll_slots]libc.pollfd = undefined;