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, 5 insertions, 0 deletions

diff --git a/src/pardes.zig b/src/pardes.zig
index 29a9ab3a..a38eb837 100644
--- a/src/pardes.zig
+++ b/src/pardes.zig
@@ -72,6 +72,8 @@ pub const Turn = struct {
     /// A request that changes a pane was parked for want of quiet.
     parked: bool = false,
     wake_parked: ?*const fn (?*anyopaque) void = null,
+    /// Answers the reads the core holds, with the turn, as it is given up.
+    answer_held: ?*const fn (?*anyopaque) void = null,
     wake_ctx: ?*anyopaque = null,
     /// Bumped each time the editor has performed what the core asked of it,
     /// so a request that asked for something -- a save, a shell -- can be
@@ -174,6 +176,9 @@ pub const Turn = struct {
     }
 
     fn release(t: *Turn) void {
+        // Whatever the holder just did may be what a held read waits for,
+        // and answering it takes the core, so before letting go.
+        if (t.answer_held) |f| f(t.wake_ctx);
         const woken = t.out == 0 and t.parked;
         if (woken) t.parked = false;
         t.mutex.unlock(t.io.?);