Rename all sexp directories, files, identifiers, and references to sx.
artdag/ excluded (separate media processing DSL).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Node 20 from Debian packages — needed to run test_sexp_js.py which
verifies JS renderer output matches Python renderer output.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
S-expression parser, evaluator, and primitive registry in shared/sexp/.
109 unit tests covering parsing, evaluation, special forms, lambdas,
closures, components (defcomp), and 60+ pure builtins.
Test infrastructure: Dockerfile.unit (tier 1, fast) and
Dockerfile.integration (tier 2, ffmpeg). Dev watch mode auto-reruns
on file changes. Deploy gate blocks push on test failure.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
