A bad event record says what is wrong with it

`bad event syntax` said nothing of which: now it says a report record
(I D i d) is not written back, a range ends before it starts, or what a
record looks like when the line is not one.

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

1 files changed, 3 insertions, 3 deletions

diff --git a/src/ninep/events.zig b/src/ninep/events.zig
index 8b8f8637..868364a6 100644
--- a/src/ninep/events.zig
+++ b/src/ninep/events.zig
@@ -726,14 +726,14 @@ pub fn writeEvent(p: *Pardes, req: Req, id: usize) Reply {
         while (check.next()) |r| {
             switch (r.action) {
                 .body_look, .tag_look, .body_exec, .tag_exec => {},
-                else => return tree.failText(req.tag, E.INVAL, tree.e_bad_event),
+                else => return tree.failText(req.tag, E.INVAL, tree.e_bad_event ++ ": only a look or exec (L l X x) is written back"),
             }
             const n = if (r.action.onTag()) tag.len else body.len;
-            if (r.q0 > r.q1) return tree.failText(req.tag, E.INVAL, tree.e_bad_event);
+            if (r.q0 > r.q1) return tree.failText(req.tag, E.INVAL, tree.e_bad_event ++ ": its range ends before it starts");
             // Well formed, but not a range of this text: say which.
             if (r.q1 > n) return tree.failText(req.tag, E.INVAL, if (r.action.onTag()) "range past end of tag" else "range past end of body");
         }
-        if (check.i != req.data.len) return tree.failText(req.tag, E.INVAL, tree.e_bad_event);
+        if (check.i != req.data.len) return tree.failText(req.tag, E.INVAL, tree.e_bad_event ++ ": a record is <origin><action><q0> <q1> <flag> <count> <text>, a line each");
     }
     var run: EventReader = .{ .data = req.data };
     while (run.next()) |r| {