Add Claude init, ignored by Rbuildignore.

Author: njhenry

.Rbuildignore

@@ -1,6 +1,6 @@
 ^LICENSE\.md$
-^CLAUDE\.md$
 Makefile
 ^_pkgdown\.yml$
 ^\.github$
+^\.claude$
 ^docs$

.claude/CLAUDE.md

@@ -0,0 +1,50 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Overview
+
+`versioning` is an **R package** that parses YAML config files to simplify versioned data pipeline management. It provides a `Config` R6 class for accessing config values and dispatching file reads/writes based on extension.
+
+## Common Commands
+
+```bash
+make build        # Build the package tarball
+make install      # Build and install locally
+make build-docs   # Regenerate man pages from roxygen2 comments (devtools::document())
+make check        # Run CRAN check (devtools::check(cran = TRUE))
+```
+
+Run tests (in an R session):
+```r
+devtools::test()                              # All tests
+testthat::test_file("tests/testthat/test-example_config.R")  # Single file
+```
+
+## Documentation
+
+Docs are built with **pkgdown** and auto-deployed to GitHub Pages on push to `main` via `.github/workflows/pkgdown.yml`.
+
+- When adding a new exported function or class, add a `@export` roxygen tag and run `make build-docs` to regenerate `NAMESPACE` and `man/` files.
+- The pkgdown reference page layout is configured in `_pkgdown.yml` — update it when adding new public symbols.
+- Package version is in `DESCRIPTION`; update it when releasing.
+
+## Architecture
+
+### Core Components
+
+**[R/Config.R](R/Config.R)** — The main `Config` R6 class. Loaded from a YAML file with two special top-level keys:
+- `directories`: named list of directory definitions, each with `path`, optional `versioned: true`, and a `files` map of logical names to filenames.
+- `versions`: current version strings for each versioned directory.
+
+Key methods: `$get(...)` for arbitrary config values, `$get_dir_path(dir)` for resolving directory paths (inserting version if versioned), `$get_file_path(dir, file)` for full file paths, `$read(dir, file)` and `$write(x, dir, file)` for dispatched I/O.
+
+**[R/autoread.R](R/autoread.R) / [R/autowrite.R](R/autowrite.R)** — Dispatcher functions that route file I/O to the appropriate reader/writer based on file extension. `get_file_reading_functions()` and `get_file_writing_functions()` return the extension→function maps. Supported formats: csv, rds, rda, yaml, txt, shp, tif, xls/xlsx, dta, dbf, and additional sf/terra spatial drivers.
+
+**[R/utilities.R](R/utilities.R)** — `pull_from_list(x, ..., fail_if_null)` for safe nested list indexing with informative errors.
+
+**[R/misc.R](R/misc.R)** — Internal helpers: `qstop()` (stop without call context), `require_namespace_or_stop(pkg)` (lazy-load optional packages).
+
+### Dependency Strategy
+
+Core imports: `R6`, `assertthat`, `glue`, `yaml`. Heavy optional packages (`data.table`, `sf`, `terra`, `readxl`, `haven`, `foreign`) are listed under `Suggests:` and loaded lazily via `require_namespace_or_stop()` only when the relevant file format is used.