Phase 1: s-expression core library + test infrastructure

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>

test/Dockerfile.integration

@@ -0,0 +1,38 @@
+# Tier 2: Integration tests — needs ffmpeg, full artdag pipeline
+# Covers: artdag/test/, artdag/l1/ loose test files (non-GPU)
+FROM python:3.11-slim
+
+ENV PYTHONDONTWRITEBYTECODE=1 \
+    PYTHONUNBUFFERED=1 \
+    PYTHONPATH=/app
+
+WORKDIR /app
+
+# System deps for media processing tests
+RUN apt-get update && apt-get install -y --no-install-recommends \
+      ffmpeg \
+      ca-certificates \
+    && rm -rf /var/lib/apt/lists/*
+
+# Python deps
+COPY shared/requirements.txt ./requirements-shared.txt
+RUN pip install --no-cache-dir -r requirements-shared.txt
+
+COPY artdag/core/ ./artdag/core/
+RUN pip install --no-cache-dir -e artdag/core/[all,dev]
+
+COPY artdag/common/ ./artdag/common/
+RUN pip install --no-cache-dir -e artdag/common/
+
+COPY artdag/l1/requirements.txt ./requirements-l1.txt
+RUN pip install --no-cache-dir -r requirements-l1.txt
+
+# Copy full L1 + test suite
+COPY artdag/l1/ ./artdag/l1/
+COPY artdag/test/ ./artdag/test/
+COPY shared/ ./shared/
+
+CMD ["python", "-m", "pytest", \
+     "artdag/test/", \
+     "-v", "--tb=short", \
+     "-k", "not gpu and not cuda"]