Hold a read that has nothing yet and answer it when its file has news

A following log, event, pty/data or a pty/run before its answer used to
answer .again and wait for a wakeAll, which only the parked-write path
asked for, so the band-aid had every queue push set turn.parked. Now the
core keeps such a read (ctlfs.hold) and, as the turn is given up after
anything that queued a record, ran a command out or closed a pane,
answers it on its own connection, the way factotum answers the log reads
it keeps and acme an event read. Only a read the engine still holds
parked is answered, because cloud9 tells the backend nothing of a
Tflush, so a flushed read spends no record.

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

1 files changed, 6 insertions, 0 deletions

diff --git a/src/fs.zig b/src/fs.zig
index 8e2c52a1..50a446dc 100644
--- a/src/fs.zig
+++ b/src/fs.zig
@@ -1243,6 +1243,12 @@ pub const Namespace = struct {
     panes: [MAX_PANES]tree.pane.State = @splat(.{}),
     listeners: u16 = 0,
     origin: u8 = 'K',
+    /// Reads that found nothing yet, one per open that can wait: the log's
+    /// and a run's opens, and one event and one pty/data reader a pane.
+    held: [tree.screen.snapshot_slots + tree.pty.run_slots + 2 * MAX_PANES]?tree.Held = @splat(null),
+    /// Something a held read may be waiting on changed since they were last
+    /// answered: a record queued, a run answered, a pane gone.
+    news: bool = false,
     /// The editor-wide event ring: panes made, renamed, saved and closed, and
     /// what the editor said. Recorded whether or not anyone reads /log.
     log: tree.events.Queue = .{ .cap = limits.log_bytes },