A malformed flag write reads as EINVAL through a mount again

The refusal `takes 1 or 0` matched none of 9ns's words, so a mount turned it into EIO. It now starts `bad flag:`, which 9ns maps to EINVAL, as it did the bare errno before.

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

1 files changed, 2 insertions, 2 deletions

diff --git a/src/ninep/pane.zig b/src/ninep/pane.zig
index d2b2a791..f87e43a6 100644
--- a/src/ninep/pane.zig
+++ b/src/ninep/pane.zig
@@ -507,7 +507,7 @@ fn writeRange(req: Req, pane: *Pane, file: PaneFile) Reply {
 
 fn writeFlag(p: *Pardes, req: Req, pane: *Pane, file: PaneFile) Reply {
     const word = std.mem.trim(u8, req.data, " \t\r\n");
-    if (!std.mem.eql(u8, word, "1") and !std.mem.eql(u8, word, "0")) return tree.failText(req.tag, E.INVAL, "takes 1 or 0");
+    if (!std.mem.eql(u8, word, "1") and !std.mem.eql(u8, word, "0")) return tree.failText(req.tag, E.INVAL, "bad flag: takes 1 or 0");
     const on = word[0] == '1';
     const pf = &pane.fs;
     switch (file) {
@@ -875,7 +875,7 @@ test "the flag files read and write the state acme kept behind ctl verbs" {
         try testing.expectEqual(@as(u64, 2), call(p, .{ .tag = 1, .op = .getattr, .node = node }).reply.attr.size);
         for ([_][]const u8{ "", "yes", "2", "0 1", "true" }) |bad| {
             try testing.expectEqual(E.INVAL, wr(p, node, bad).errno());
-            try testing.expectEqualStrings("takes 1 or 0", wr(p, node, bad).reply.ename);
+            try testing.expectEqualStrings("bad flag: takes 1 or 0", wr(p, node, bad).reply.ename);
         }
     }