Addresses search a line at a time as sam does, say why they fail, and a failed addr leaves no address

addr's regexps ran mvzr over text[from..hi]: ^ and $ anchored only at the
slice's ends, . matched newlines, the search never wrapped, and every
failure read as bad address syntax. The regexps stay mvzr's, called the
way sam searches (editors/acme/regx.c): one line per haystack, so ^ and $
fall at line boundaries and . never crosses a newline; a pattern naming
\\n runs over the whole text with its . made [^\\n]; /re/ wraps unless
limit is set, and ?re? takes the last match before the range. The ceiling
(mvzr's first alternative, not sam's longest) is documented. A failed
address says why (no match for regexp, address out of range, bad regular
expression), and a failed write to addr leaves no address, so data and
xdata refuse until the next good one instead of writing at the old range.

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

1 files changed, 2 insertions, 0 deletions

diff --git a/src/ninep/tree.zig b/src/ninep/tree.zig
index e9c6b8ea..3ce7e758 100644
--- a/src/ninep/tree.zig
+++ b/src/ninep/tree.zig
@@ -681,6 +681,8 @@ fn setattr(p: *Pardes, req: Req, target: Target) Reply {
     if (req.truncate) switch (target) {
         .pane => |t| {
             const id = p.paneBySerial(t.serial) orelse return Reply.fail(req.tag, E.NOENT);
+            if ((t.file == .data or t.file == .xdata) and p.panes[id].?.fs.addr_failed)
+                return failText(req.tag, E.INVAL, pane.e_addr_failed);
             if (pane.truncate(p, p.panes[id].?, t.file) != .ok) return Reply.fail(req.tag, E.NOMEM);
         },
         .top => {},