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/ninep/events.zig b/src/ninep/events.zig
index d7079c5e..f58d970e 100644
--- a/src/ninep/events.zig
+++ b/src/ninep/events.zig
@@ -101,7 +101,7 @@ pub const Queue = struct {
 /// One record per read; `.again` holds the read until a record arrives.
 pub fn readQueue(p: *Pardes, req: Req, q: *Queue) Reply {
     const record = q.peek() orelse return .{ .tag = req.tag, .status = .again };
-    if (req.size < record.len) return Reply.fail(req.tag, E.INVAL);
+    if (req.size < record.len) return tree.failText(req.tag, E.INVAL, "invalid read: shorter than the record waiting");
     const out = p.fs.stage(p.gpa);
     out.appendSlice(p.gpa, record) catch return Reply.fail(req.tag, E.NOMEM);
     q.pop();
@@ -477,7 +477,7 @@ pub fn writeLog(p: *Pardes, req: Req) Reply {
     // what was there and waits for what comes after, as tail -n0 -f does.
     if (std.mem.eql(u8, word, "follow new")) {
         slot.pos = slot.bytes.len;
-    } else if (!std.mem.eql(u8, word, "follow")) return Reply.fail(req.tag, E.INVAL);
+    } else if (!std.mem.eql(u8, word, "follow")) return tree.failText(req.tag, E.INVAL, "invalid write to log: it takes `follow` or `follow new`");
     slot.follow = true;
     return .{ .tag = req.tag, .written = @intCast(req.data.len) };
 }