A regular expression search comes back: costly patterns refused, long lines windowed, 300 ms deadline

mvzr backtracks with no bound on its work (a*a*a*a*x over a hundred a's takes a
second, each repeat multiplying by the haystack length), and a search runs holding
the editor's turn, so one pasted pattern froze the editor. pardes does not write or
vendor a regex engine, so regexp.zig bounds what it hands mvzr: more than four
repeats is refused, a line longer than a window sized from measured worst cases is
searched in half-overlapping windows, and a deadline stops the search. addr names
each failure; normal s/S keeps what it found. The prescan also stops reading an
escaped backslash before n as a newline, and ends a class where mvzr does.

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

1 files changed, 2 insertions, 1 deletions

diff --git a/.agents/skills/pardes-9p/SKILL.md b/.agents/skills/pardes-9p/SKILL.md
index a9cecaf8..330f029d 100644
--- a/.agents/skills/pardes-9p/SKILL.md
+++ b/.agents/skills/pardes-9p/SKILL.md
@@ -140,7 +140,8 @@ is why copying one onto another is all that acme's `addr=dot`, `dot=addr` and
 `/pattern/`, `2+1`), whose regexps are mvzr's searched as sam searches:
 `^`/`$` match at any line's start and end, `.` and `[^...]` never match a
 newline, the leftmost match wins (the first alternative there, not the
-longest), and `/re/` wraps unless `limit` is set. A failed address says
+longest), `/re/` wraps unless `limit` is set, and since mvzr backtracks a
+pattern with more than four `*`/`+`/`{}` is refused. A failed address says
 why (`no match for regexp`, `address out of range`) and leaves no address:
 `data` refuses until the next good one, so a missed target is never
 written at the old one. Moving `dot` scrolls the pane to it. `limit` bounds a