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.unit

@@ -0,0 +1,51 @@
+# Tier 1: Unit tests — pure Python, no services, no DB, no Redis
+# Covers: shared/, artdag/core/, artdag/l1/tests/, artdag/l1/sexp_effects/
+FROM python:3.11-slim
+
+ENV PYTHONDONTWRITEBYTECODE=1 \
+    PYTHONUNBUFFERED=1 \
+    PYTHONPATH=/app
+
+WORKDIR /app
+
+# Install shared deps (includes pytest, pytest-asyncio)
+COPY shared/requirements.txt ./requirements-shared.txt
+RUN pip install --no-cache-dir -r requirements-shared.txt pytest-watch
+
+# Install artdag core as editable package
+COPY artdag/core/ ./artdag/core/
+RUN pip install --no-cache-dir -e artdag/core/[dev]
+
+# Install artdag common
+COPY artdag/common/ ./artdag/common/
+RUN pip install --no-cache-dir -e artdag/common/
+
+# Install L1 deps that unit tests need (not the heavy ones)
+COPY artdag/l1/requirements.txt ./requirements-l1.txt
+RUN pip install --no-cache-dir -r requirements-l1.txt 2>/dev/null || true
+
+# Copy test subjects
+COPY shared/ ./shared/
+COPY artdag/l1/tests/ ./artdag/l1/tests/
+COPY artdag/l1/sexp_effects/ ./artdag/l1/sexp_effects/
+COPY artdag/l1/app/ ./artdag/l1/app/
+COPY artdag/l1/database.py ./artdag/l1/database.py
+COPY artdag/l1/ipfs_client.py ./artdag/l1/ipfs_client.py
+COPY artdag/l1/storage_providers.py ./artdag/l1/storage_providers.py
+COPY artdag/l1/cache_manager.py ./artdag/l1/cache_manager.py
+COPY artdag/l1/claiming.py ./artdag/l1/claiming.py
+COPY artdag/l1/path_registry.py ./artdag/l1/path_registry.py
+COPY artdag/l1/celery_app.py ./artdag/l1/celery_app.py
+COPY artdag/l1/pyproject.toml ./artdag/l1/pyproject.toml
+
+# Default: run all unit tests
+CMD ["python", "-m", "pytest", \
+     "shared/", \
+     "artdag/core/tests/", \
+     "artdag/core/artdag/sexp/", \
+     "artdag/l1/tests/", \
+     "artdag/l1/sexp_effects/", \
+     "-v", "--tb=short", \
+     "--ignore=artdag/l1/tests/test_jax_primitives.py", \
+     "--ignore=artdag/l1/tests/test_jax_pipeline_integration.py", \
+     "-k", "not gpu and not cuda"]