QR tests MUST use native language libraries, not qrencode CLI.
If the sandbox doesn't have the library, the test should FAIL
honestly so we know what to fix in the sandbox image.
Also adds CLAUDE.md rule to prevent future attempts to replace
native library QR tests with CLI subprocess calls.
- Fortran: use dlopen/dlsym at runtime instead of direct linking
(sandbox doesn't pass -lqrencode to gfortran)
- Both: try libqrencode.so.4, .so.3, .so in order
- Perl: use Text::QRCode (pure Perl, pre-installed) instead of Imager::QRCode
- Elixir: try Erlang :qrcode module, fallback to CLI
- OCaml: use Unix.open_process_in (no ctypes in compiled mode)
- Fortran: direct C FFI binding (requires -lqrencode at link)
Native QR generation for each language's ecosystem:
- 27 languages use package manager QR libraries (qrcode, rqrcode, ZXing, etc.)
- 10 languages use C FFI to libqrencode (dlopen, ISO_C_BINDING, @cImport, critcl)
- 2 shell languages use qrencode CLI (native shell paradigm)
- 1 language (Prolog) uses C FFI with CLI fallback
Section 9 added to test-sdk.sh with get_qr_file() mapping and
QR:unsandbox-qr-ok:ROWS pattern validation across the hydra matrix.
