ci: added GitHub Actions (tests, import-independence, install) + ruff lint

Author: abhiprd2000

.github/workflows/ci.yml

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+name: CI
+
+# Runs on every push to main and every pull request targeting main.
+# Scope is deliberate: dependency-light unit tests and import checks only.
+# The full experiments (CNN training, DoWhy counterfactuals, cross-domain runs)
+# require TensorFlow, DoWhy, a GPU, and licensed datasets that are not available
+# in CI. Those are run on a workstation and recorded in EXPERIMENTS.md.
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  test:
+    name: tests (py${{ matrix.python-version }})
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        python-version: ["3.11", "3.12", "3.13"]
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Python ${{ matrix.python-version }}
+        uses: actions/setup-python@v5
+        with:
+          python-version: ${{ matrix.python-version }}
+          cache: pip
+
+      - name: Install core dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install -r requirements.txt
+          pip install pytest
+
+      - name: Run unit tests
+        run: pytest test/ -v
+
+  import-independence:
+    name: import-independence (no TensorFlow)
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+          cache: pip
+
+      - name: Install core dependencies only
+        run: |
+          python -m pip install --upgrade pip
+          pip install -r requirements.txt
+
+      - name: Assert TensorFlow is absent
+        run: |
+          python - <<'PY'
+          import importlib.util, sys
+          if importlib.util.find_spec("tensorflow") is not None:
+              sys.exit("TensorFlow is installed; this job must run without it.")
+          print("confirmed: TensorFlow not installed")
+          PY
+
+      - name: Import dependency-light subpackages
+        run: |
+          python - <<'PY'
+          import importlib
+          for mod in ("cnsd.causal", "cnsd.physics", "cnsd.config", "cnsd.scm"):
+              importlib.import_module(mod)
+              print(f"imported {mod} without TensorFlow")
+          PY
+
+  install:
+    name: editable install
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+          cache: pip
+
+      - name: Install package (editable, core extras)
+        run: |
+          python -m pip install --upgrade pip
+          pip install -e .
+
+      - name: Import installed package
+        run: python -c "import cnsd; print('cnsd installed and importable')"

.github/workflows/lint.yml

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+name: Lint
+
+# Static checks: Ruff handles both linting and formatting in a single tool.
+# Fast (seconds), no project dependencies needed, runs on every push and PR.
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+concurrency:
+  group: lint-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  ruff:
+    name: ruff (lint + format)
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+
+      - name: Install Ruff
+        run: pip install ruff
+
+      # Linting: flags unused imports, undefined names, common bugs.
+      - name: Ruff lint
+        run: ruff check .
+
+      # Formatting: verifies code matches the formatter (does not modify it).
+      # Run `ruff format .` locally to fix before pushing.
+      - name: Ruff format check
+        run: ruff format --check .

pyproject.toml

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+# Tool configuration only.
+#
+# Packaging is still handled by setup.py, the developer tooling (Ruff, pytest) in their standard modern location.
+
+[tool.ruff]
+line-length = 100
+target-version = "py311"
+# Directories that are generated, vendored, or not part of the package source.
+extend-exclude = ["build", "dist", "*.egg-info", "experiments_archive"]
+
+[tool.ruff.lint]
+# A pragmatic, not maximal, rule set. Catches the real bug classes this project
+# has actually hit (unused/undefined imports, name errors) without drowning a
+# research codebase in stylistic noise.
+select = [
+    "E",   # pycodestyle errors
+    "F",   # pyflakes (unused imports, undefined names, the bugs we kept hitting)
+    "I",   # import sorting
+    "B",   # flake8-bugbear (likely-bug patterns)
+    "UP",  # pyupgrade (modernize syntax)
+    "W",   # pycodestyle warnings
+]
+ignore = [
+    "E501",  # line length is enforced by the formatter, not the linter
+    "B008",  # function calls in argument defaults (common, intentional here)
+]
+
+[tool.ruff.lint.per-file-ignores]
+# Test files and examples may use imports for side effects / fixtures.
+"test/*" = ["F401", "F811"]
+"examples/*" = ["F401"]
+
+[tool.ruff.format]
+quote-style = "single"
+docstring-code-format = true
+
+[tool.pytest.ini_options]
+testpaths = ["test"]
+python_files = ["test_*.py", "*_test.py"]
+addopts = "-v"