A desktop session holds 64 panes, and every route that finds none free says so

Sixteen panes was far too few for a real session. MAX_PANES is now 64 on a
desktop and stays 16 on the board; the 48 more slots cost about 3.7 KB each
in fixed tables (the core 1.33 to 1.45 MB, its surface 19 to 72 KB), and a
pane itself (84 KB and its terminal) is allocated only when it opens. At the
cap, pane/new fails with `pane/new: no pane slots: 64 max` and an err
record rather than a bare ENFILE, a 9P look or exec that would open a pane
fails its write with the same words and reads back empty, and New, Tty,
Tutor and Alt-n say it on the message row (their ctl writes fail with it).

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

1 files changed, 4 insertions, 0 deletions

diff --git a/src/fs.zig b/src/fs.zig
index 21ccc94e..88ffb4a3 100644
--- a/src/fs.zig
+++ b/src/fs.zig
@@ -1274,6 +1274,10 @@ pub const Namespace = struct {
     /// 0 the workspace's, a column's its index + 1; and whether the newline
     /// that ended its last write is held back.
     header_rewrite: ?u32 = null,
+    /// A look or exec a 9P write made found every pane slot taken; the
+    /// write fails with what was said, kept at the head of `ename`.
+    no_pane_slot: bool = false,
+    no_pane_slot_len: u16 = 0,
     header_held: bool = false,
     late_failure: [256]u8 = undefined,
     late_failure_len: u16 = 0,