Record /log whether or not anyone reads it, with the editor's messages in it

/log is now one ring (64 KiB, 4 KiB on the board) that records new, del,
rename and save, and a msg line for everything the editor says. An open
freezes it, so cat log shows what happened lately and ends; writing
follow to that same open makes reads past it wait for newer records, and
a follower the ring outran reads lost N first.

The message log keeps the pane's serial, not its reusable slot.

A test now fails when the tree serves a file /README never mentions; it
caught pty/status, now documented along with typing through pty/data.

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

1 files changed, 7 insertions, 1 deletions

diff --git a/src/ninep/screen.zig b/src/ninep/screen.zig
index 60fb5951..245a31ef 100644
--- a/src/ninep/screen.zig
+++ b/src/ninep/screen.zig
@@ -11,7 +11,13 @@ const Req = tree.Req;
 const Reply = tree.Reply;
 const E = tree.E;
 
-pub const Snapshot = struct { node: u64 = 0, bytes: ?[]const u8 = null };
+pub const Snapshot = struct {
+    node: u64 = 0,
+    bytes: ?[]const u8 = null,
+    /// /log only: this open waits for records after `bytes`, from `next`.
+    follow: bool = false,
+    next: u64 = 0,
+};
 pub const snapshot_slots = 32;
 
 pub fn render(p: *Pardes) ![]u8 {