Every EINVAL a write gets says why; DEL in an exec or look line is a control character

An empty name, a word written to log other than follow, a data, sel, dot
or dirty write to a pane with no text, a truncate other than to zero,
and a control character in a look line written through a held open were
refused with no words, logged as `Invalid argument`. Each says its reason
now; and DEL is refused in exec and look lines as in names.

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

1 files changed, 1 insertions, 1 deletions

diff --git a/src/ninep/cols.zig b/src/ninep/cols.zig
index 7f78522a..6fdcda07 100644
--- a/src/ninep/cols.zig
+++ b/src/ninep/cols.zig
@@ -166,7 +166,7 @@ pub fn writeExec(p: *Pardes, req: Req, serial: ?u32) Reply {
     while (lines.next()) |raw| {
         const line = std.mem.trim(u8, raw, " \t\r");
         if (line.len == 0) continue;
-        for (line) |c| if (c < ' ' and c != '\t') return tree.failText(req.tag, E.INVAL, pardes.ctlfs.ctl.e_control);
+        for (line) |c| if ((c < ' ' and c != '\t') or c == 0x7f) return tree.failText(req.tag, E.INVAL, pardes.ctlfs.ctl.e_control);
         if (pardes.ctlfs.ctl.tooLong(req, line)) |refusal| return refusal;
         // A pane's word (Undo, Msg, Save) is no word of a tag no pane owns:
         // refused as the root's ctl refuses it, never done at whichever