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, 2 insertions, 2 deletions

diff --git a/src/fs.zig b/src/fs.zig
index 4414c150..352aa0c4 100644
--- a/src/fs.zig
+++ b/src/fs.zig
@@ -224,12 +224,12 @@ pub fn osHandle(p: *pardes.Pardes, req: Req) Reply {
                 if (fd < 0) return Reply.fail(req.tag, E.PERM);
                 defer _ = libc.close(fd);
                 if (req.op == .setattr) {
-                    if (!req.truncate or req.off != 0 or libc.ftruncate(fd, 0) != 0) return Reply.fail(req.tag, E.INVAL);
+                    if (!req.truncate or req.off != 0 or libc.ftruncate(fd, 0) != 0) return tree.failText(req.tag, E.INVAL, "invalid truncate: only to zero");
                     var truncated = attr;
                     truncated.size = 0;
                     return .{ .tag = req.tag, .attr = truncated };
                 }
-                if (req.off > std.math.maxInt(i64)) return Reply.fail(req.tag, E.INVAL);
+                if (req.off > std.math.maxInt(i64)) return tree.failText(req.tag, E.INVAL, "invalid offset: past what a file may hold");
                 if (libc.lseek(fd, @intCast(req.off), libc.SEEK.SET) < 0) return Reply.fail(req.tag, E.IO);
                 if (req.op == .write) {
                     const written = libc.write(fd, req.data.ptr, req.data.len);