A detached session with no frontend takes its size from the root ctl

A --detach session nobody is attached to stayed 80x24, too small for an
agent's panes, and nothing could change it. The root ctl takes size <cols>
<rows> while no frontend is attached (refused while one owns the size), and
a client that attaches later still sets its own (the server compares with
the core's size). Documented with the 80x24 default.

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

1 files changed, 3 insertions, 1 deletions

diff --git a/src/detached/server.zig b/src/detached/server.zig
index 8f45135a..af299051 100644
--- a/src/detached/server.zig
+++ b/src/detached/server.zig
@@ -1076,7 +1076,9 @@ pub const Session = struct {
             rows = if (rows == 0) c.rows else @min(rows, c.rows);
         }
         var regridded = false;
-        if (cols != 0 and (cols != s.cols or rows != s.rows)) {
+        // Against the core's size too: a root ctl `size` may have set it
+        // while nobody was attached.
+        if (cols != 0 and (cols != s.cols or rows != s.rows or cols != s.core.screen_w or rows != s.core.screen_h)) {
             s.cols = cols;
             s.rows = rows;
             for (&s.clients) |*c| c.need_full = true;