feat: add multi-engine regex flavour support

engines/perl/NOTICE.txt

@@ -0,0 +1,68 @@
+Legacy WebPerl runtime notices
+==============================
+
+This directory contains the unmodified WebPerl v0.09-beta prebuilt runtime,
+released in 2019 and explicitly treated by regex-tools as legacy beta software.
+
+WebPerl
+-------
+
+Project: https://github.com/haukex/webperl
+Release: v0.09-beta
+Commit: 6f2173d29a2c2e3536e1de75ff5d291ae96ab348
+Copyright (c) 2018 Hauke Daempfling, Leibniz Institute of Freshwater Ecology
+and Inland Fisheries (IGB), Berlin, Germany.
+
+WebPerl is distributed under the same terms as Perl 5: either the GNU General
+Public License version 1 or later, or the Artistic License supplied with Perl 5.
+The complete upstream texts are included as LICENSE-WebPerl-GPL.txt and
+LICENSE-WebPerl-Artistic.txt.
+
+Perl
+----
+
+The binary and data pack contain Perl v5.28.1 and its core library. Perl 5 is
+distributed under the same GNU GPL / Artistic dual-license terms described
+above. Exact upstream source is available from:
+
+https://github.com/Perl/perl5/tree/v5.28.1
+
+Emscripten
+----------
+
+The generated loader and WebAssembly runtime were built by upstream WebPerl
+with Emscripten 1.38.28. Emscripten is dual-licensed under the MIT and
+University of Illinois/NCSA licenses. The upstream 1.38.28 license text,
+including its bundled-code notices, is included as LICENSE-Emscripten.txt.
+
+Bundled CPAN additions
+----------------------
+
+The upstream prebuilt data pack also contains the modules selected by
+WebPerl's pinned build:
+
+- Cpanel::JSON::XS 4.09 — same terms as Perl 5;
+- Devel::StackTrace 2.03 — Artistic License 2.0; its upstream distribution
+  license is included as LICENSE-Devel-StackTrace-Artistic-2.0.txt; and
+- Future 0.39 — same terms as Perl 5.
+
+The Devel::StackTrace license was reproduced byte-for-byte from
+https://www.cpan.org/authors/id/D/DR/DROLSKY/Devel-StackTrace-2.03.tar.gz
+(SHA-256 7618cd4ebe24e254c17085f4b418784ab503cb4cb3baf8f48a7be894e59ba848).
+
+regex-tools uses Cpanel::JSON::XS only as the fixed bridge's bounded JSON
+codec. It does not load Devel::StackTrace, Future, or WebPerl's JavaScript
+interop module on the normal engine path. Those files remain present because
+emperl.data is the unmodified, checksummed upstream prebuilt pack.
+
+Security boundary
+-----------------
+
+The upstream generated emperl.js has one JavaScript eval(code) call in the
+optional WebPerl JavaScript-interoperability import. regex-tools neither loads
+nor calls that Perl module. User values cross the fixed bridge only as
+exact-key, byte-bounded JSON in MEMFS; the sole Perl evaluator invocation is
+the constant RegexTools::run_request(). The bounded metadata response is JSON,
+while successful replacement UTF-8 bytes use a separate fixed MEMFS binary
+file with exact worker-side length and encoding verification. Perl's
+runtime-regex eval mode and regex code assertions are disabled.