v0.1.4

.flake8

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+[flake8]
+max-line-length = 88
+extend-ignore = E203

.gitattributes

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+# Enforce Linux-style line endings for all text files
+* text=auto eol=lf

.github/workflows/ci.yml

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+name: CI
+
+on:
+  push:
+  pull_request:
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+      - name: Install lint dependencies
+        run: |
+          python -m pip install --upgrade pip
+          python -m pip install .[dev]
+      - name: Lint
+        run: flake8 src tests tools
+      - name: Validate packaged registry
+        run: python tools/check_registry.py
+      - name: Validate notebooks
+        run: python tools/check_notebooks.py
+      - name: Check notebook exports
+        run: python tools/export_notebooks.py --check
+      - name: Check README sync
+        run: python tools/gen_readme.py --check
+
+  docs-check:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+      - name: Install docs extras
+        run: |
+          python -m pip install --upgrade pip
+          python -m pip install .[docs]
+      - name: Export notebooks and README
+        run: |
+          python tools/export_notebooks.py --check
+          python tools/gen_readme.py --check
+      - name: Build docs
+        run: mkdocs build --strict
+
+  test:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python-version: ["3.10", "3.11", "3.12", "3.13"]
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-python@v5
+        with:
+          python-version: ${{ matrix.python-version }}
+      - name: Install
+        run: |
+          python -m pip install --upgrade pip
+          python -m pip install .[test]
+      - name: Test
+        run: pytest
+
+  build-dist:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+      - name: Install build dependencies
+        run: |
+          python -m pip install --upgrade pip
+          python -m pip install build twine
+      - name: Build distributions
+        run: python -m build
+      - name: Validate metadata
+        run: python -m twine check dist/*
+      - name: Check packaged files
+        run: python tools/check_dist.py dist
+      - name: Install built wheel and smoke-test it
+        run: |
+          python -m pip install --force-reinstall --no-deps dist/*.whl
+          python - <<'PY'
+          import atomref as ar
+
+          assert ar.get_covalent_radius('C') == 0.76
+          assert ar.get_vdw_radius('C') == 1.77
+          assert 'atomic_radius' in ar.list_quantities()
+          assert 'rahm2016' in ar.list_dataset_ids('atomic_radius', usage_role='support')
+          PY

.github/workflows/docs.yml

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+name: Docs
+
+on:
+  push:
+    branches: [main, master]
+  workflow_dispatch:
+
+jobs:
+  build-docs:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+      - name: Install docs extras
+        run: |
+          python -m pip install --upgrade pip
+          python -m pip install .[docs]
+      - name: Check generated files
+        run: |
+          python tools/export_notebooks.py --check
+          python tools/gen_readme.py --check
+      - name: Build docs
+        run: mkdocs build --strict

CHANGELOG.md

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+# Changelog
+
+## 0.1.4 - 2026-03-15
+
+### Added
+
+- `LookupResult.transfer_depth`, which records how many transfer steps were
+  involved in the returned numeric value.
+- Explicit nested-policy safeguards for `LinearTransfer` via:
+  - `fit_sources`
+  - `fit_max_depth`
+  - `prediction_sources`
+  - `prediction_max_depth`
+- Regression tests covering generic-policy cycles, wrapper-policy cycles,
+  conservative nested-fit defaults, and explicit opt-in for deeper nested
+  linear workflows.
+
+### Changed
+
+- Nested policy-backed linear transfers are now guarded in two phases:
+  conservative defaults are used for fit training, while one additional nested
+  completion step remains allowed at prediction time.
+- Linear-transfer fitting now distinguishes direct predictor values from nested
+  policy-derived predictor values.
+- Cycle detection now tracks both generic policies and wrapper policies using a
+  context-local activation stack, so recursion through freshly materialized
+  wrapper policies is detected reliably and safely.
+- Radii and X–H convenience helpers now resolve through wrapper-aware cycle
+  tracking rather than materializing a fresh generic policy for each public
+  lookup call.
+
+### Documentation
+
+- Expanded the transfer and policy docs to explain nested-policy safeguards,
+  `transfer_depth`, and cycle detection.
+- Added guidance on when chained correlations are scientifically reasonable and
+  how to opt in deliberately when broader fit training is desired.
+
+## 0.1.3 - 2026-03-15
+
+### Added
+
+- Support for using generic policies and wrapper policies as transfer sources in
+  `SubstitutionTransfer` and `LinearTransfer`.
+- Public `atomref.xh` module docs and examples for policy-backed predictor
+  workflows.
+
+### Changed
+
+- `LinearTransfer` now treats predictors as **sources** rather than only raw
+  datasets, while still keeping the current runtime to one predictor at a time.
+- Generic policy resolution now supports blocked element keys, which is used by
+  the X–H helper to prevent invalid `H` parent-element lookups.
+- Transfer results now preserve nested-policy provenance through
+  `resolved_from` and explanatory notes when a policy source is involved.
+
+## 0.1.2 - 2026-03-15
+
+### Added
+
+- New `xh_bond_length` quantity family.
+- Packaged provisional X–H dataset `csd_legacy_xh_cno` with ConQuest/CSD
+  hydrogen-normalisation targets for `C`, `N`, and `O`.
+- New `atomref.xh` convenience layer with `XHPolicy`, `DEFAULT_XH_POLICY`, set
+  listing helpers, and X–H lookup helpers.
+
+### Documentation
+
+- Added X–H dataset and API pages.
+- Documented the provisional scope of X–H support in `0.1.x` and the planned
+  broader follow-up in `0.2.x`.
+
+## 0.1.1 - 2026-03-15
+
+### Added
+
+- Public generic lookup helpers `lookup_value(...)` and `get_value(...)`.
+- Tests for alias normalization, immutable metadata, non-finite-value rejection,
+  collision detection, and explicit placeholder notes.
+
+### Changed
+
+- Registry metadata returned by `get_dataset_info(...)` is now frozen so callers
+  cannot mutate the cached registry state.
+- Dataset-alias resolution now normalizes Unicode and dash variants more
+  robustly.
+- Custom-set construction and policy configuration now reject normalized-key
+  collisions and non-finite numeric values.
+- Radii-specific wrappers now reject negative override and fallback values.
+- Base and substitution lookups now emit explicit placeholder notes when the
+  returned numeric value is a dataset placeholder.
+- `LinearTransfer` now validates empty-predictor and invalid-`min_points`
+  configurations eagerly.
+- The docs now explain the distinction between quantity, domain, dataset, and
+  policy, and clarify that the current runtime supports only the `element`
+  domain.
+
+## 0.1.0 - 2026-03-15
+
+First public release.
+
+### Added
+
+- Packaged element metadata and curated radii tables.
+- Quantity-aware registry metadata that separates operational lookup quantity
+  from scientific classification and dataset usage role.
+- Provenance-aware radii policies with deterministic resolution order.
+- Substitution and linear-transfer support for restoring missing values from
+  curated support datasets.
+- Public helpers for inspecting quantities, dataset metadata, and packaged
+  built-in sets.
+- Runnable notebooks together with generated Markdown notebook pages in the
+  documentation.
+- Validation and maintenance tools for registry checks, notebook export, README
+  generation, and distribution-artifact inspection.
+
+### Documentation
+
+- Expanded dataset guides with citations and selection-oriented descriptions.
+- Added module-level API pages and notebook walkthroughs.
+- Added developer-facing curation and tooling notes.
+
+### Packaging
+
+- Built and validated wheel and source-distribution artifacts.
+- Added CI coverage for linting, tests, docs builds, notebook sync, and
+  distribution checks.