A column ctl write reads back what it touched alone

writeCtl never cleared what the last write touched before its lines ran,
so `New` through col/<n>/ctl read back the earlier write's serial too.

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

1 files changed, 13 insertions, 0 deletions

diff --git a/src/ninep/cols.zig b/src/ninep/cols.zig
index b00ecdba..efb62cfe 100644
--- a/src/ninep/cols.zig
+++ b/src/ninep/cols.zig
@@ -126,6 +126,8 @@ pub fn released(p: *Pardes, serial: ?u32) void {
 /// Delcol, Joincol, New, Tty -- one a line, each run as from that tag. What
 /// they say is the session's in the log (`msg -`), not the focused pane's.
 pub fn writeCtl(p: *Pardes, req: Req, serial: u32) Reply {
+    // What this write touched, alone, reads back (runBuiltin notes it).
+    p.fs.results_len = 0;
     p.fs.session_write = true;
     defer p.fs.session_write = false;
     var lines = std.mem.splitScalar(u8, req.data, '\n');
@@ -189,6 +191,17 @@ test "New written to a column's exec makes its scratch in the session's director
     try testing.expectEqualStrings("/project/src/+New", p.panes[p.active].?.file.?.path);
 }
 
+test "New written to a column's ctl reads back the new pane alone, as its exec does" {
+    const p = try th.withFile(testing.allocator, "x\n");
+    defer p.deinit();
+    const root_exec = @intFromEnum(tree.TopFile.exec);
+    _ = th.wr(p, root_exec, "Msg before\n");
+    const ctl_node = tree.Node.ofCol(layout.columnSerial(p, 0), .ctl);
+    try testing.expectEqual(tree.Status.ok, th.wr(p, ctl_node, "New\n").reply.status);
+    var want: [16]u8 = undefined;
+    try testing.expectEqualStrings(try std.fmt.bufPrint(&want, "{d}\n", .{p.panes[p.active].?.serial}), th.rd(p, root_exec, 0, 64).bytes);
+}
+
 /// rmdir of a column closes it when it is empty; one with panes is
 /// refused, saying so (close them, or Delcol on its ctl, which asks first).
 pub fn remove(p: *Pardes, req: Req, serial: u32, file: tree.ColFile) Reply {