diff --git a/.CLAUDE.md b/.CLAUDE.md
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+# tinyplot - AI Assistant Context
+
+## Package Overview
+
+**tinyplot** is a lightweight extension of base R graphics providing automatic legends, facets, themes, and other enhancements. Zero recursive dependencies — only base R.
+
+- Main function: `tinyplot()` (alias: `plt()`)
+- Add layers: `tinyplot_add()` / `plt_add()`
+- Themes: `tinytheme()`
+- Parameters: `tpar()`
+
+## Quick Reference
+
+When working on tinyplot interactively, always use `pkgload::load_all()` to load the development version — never `library(tinyplot)`. This ensures you're testing your local changes, not an installed copy.
+
+```r
+pkgload::load_all()
+
+# Then test interactively, e.g.
+plt(Sepal.Length ~ Petal.Length | Species, data = iris)
+```
+
+## Repository Structure
+
+- `R/` — Package source. The main entry point is `tinyplot.R` (~57KB). Plot types live in `type_*.R` files. Other key files include `legend.R`, `facet.R`, `by_aesthetics.R`, `tinytheme.R`, `tpar.R`, and `environment.R`. Input validation helpers follow the `sanitize_*.R` naming convention. Utility functions are in `utils.R`.
+- `inst/tinytest/` — Test suite (`tinytest` + `tinysnapshot`). Snapshot SVGs are in `_tinysnapshot/`.
+- `man/` — roxygen2-generated `.Rd` files.
+- `vignettes/` — Package vignettes (qmd format).
+- `SCRATCH/` — Developer scratch files and experiments (not part of the package).
+
+## Code Style & Conventions
+
+### Zero Dependency Requirement
+tinyplot has zero recursive dependencies — it imports only base R packages (`graphics`, `grDevices`, `stats`, `tools`, `utils`). All contributions must preserve this. Do not add new package dependencies under `Imports` or `Depends`.
+
+### Assignment & Syntax
+```r
+# Use = not <-
+x = 5
+
+# Use function() not \() — package requires R >= 4.0.0 compatibility
+fn = function(x) x^2
+
+# Prefer [[ over $ for element access (no partial matching, works with variables)
+legend_args[["title"]]
+settings[["datapoints"]]
+# NOT: legend_args$title, settings$datapoints
+```
+
+### No Pipes in Package Code
+The package targets R >= 4.0.0, so the base pipe `|>` (introduced in 4.1) is not available. Use intermediate variables or nested calls instead.
+
+### Line Length
+Wrap at ~80 characters. Break long function calls across lines.
+
+## Architecture & Key Patterns
+
+### Execution Flow
+The main pipeline in `tinyplot.default()` follows this sequence:
+1. Save par state and the call (for `tinyplot_add()` replay)
+2. Build a `settings` environment with all inputs
+3. Sanitize inputs: type → axes → labels → facets → datapoints
+4. Run the type's `data` function (`type_data(settings)`) to transform data
+5. Handle flipping, bubble sizing, axis limits
+6. Compute group aesthetics (colours, pch, lty, etc.)
+7. Prepare legends
+8. Draw the facet grid (if any)
+9. **Nested drawing loop**: outer loop over facets, inner loop over `by` groups — each iteration calls the type's `draw` function with per-group data
+10. Save end par state for layer recall
+
+### Type System
+Each plot type is a `tinyplot_type` S3 object created by a `type_*()` constructor:
+```r
+type_boxplot = function(range = 1.5, ...) {
+  out = list(
+    draw = draw_boxplot(range = range, ...),  # closure: does actual plotting per group
+    data = data_boxplot(...),                  # closure: preprocesses data, injects into settings
+    name = "boxplot"                           # string identifier
+  )
+  class(out) = "tinyplot_type"
+  return(out)
+}
+```
+
+- `draw` function signature: `function(iby, ix, iy, ipch, ilty, icol, ibg, ...)`
+  - Called once per group (`iby` = group index)
+  - Receives per-group subsetted data
+- `data` function signature: `function(settings, ...)`
+  - Receives the `settings` environment
+  - Reads from settings via `env2env(settings, environment(), keys)`
+  - Writes back via `env2env(environment(), settings, keys)`
+  - Can modify `datapoints`, `xlabs`, `col`, `bg`, `by`, `facet`, `group_offsets`, legend args, etc.
+
+### Settings Environment
+Individual `tinyplot()` calls store plot state in a temporary `settings` environment. Type-specific `data` functions read/write to this environment using `env2env()`. This avoids copying large objects and allows types to customize behaviour.
+
+### Package-Level State (.tinyplot_env)
+Managed via `get_environment_variable()` / `set_environment_variable()` in `environment.R`:
+- `.last_call` — last tinyplot call (used by `tinyplot_add()`)
+- `.saved_par_before` / `.saved_par_after` / `.saved_par_first` — par state for layer restoration
+- `.tpar_hooks` — theme hooks
+- `.group_offsets` — dodge offsets for layering (used by jitter-on-boxplot etc.)
+
+### recordGraphics() for Resize Handling
+Coordinate-dependent calculations (especially legends) must be wrapped in `recordGraphics()` so they replay correctly on device resize:
+```r
+recordGraphics(
+  tinylegend(legend_env),
+  list = list(legend_env = legend_env),
+  env = getNamespace("tinyplot")
+)
+```
+
+### Theme System
+Themes use `before.plot.new` hooks. Legend code must preserve/restore hooks:
+```r
+oldhook = getHook("before.plot.new")
+setHook("before.plot.new", function() par(new = TRUE), action = "append")
+plot.new()
+setHook("before.plot.new", oldhook, action = "replace")
+```
+
+### Legend Positioning
+- Inner positions: `"right"`, `"topleft"`, etc.
+- Outer positions (with `!`): `"right!"`, `"bottom!"`, etc.
+- Outer legends adjust plot margins via `par(oma=...)` and `par(mar=...)`
+
+### Group Offsets / Dodge
+When multiple groups share the same x-position (boxplot, violin, etc.), offsets are computed in the type's `data` function and stored as `group_offsets` + `offsets_axis`. These are saved to `.tinyplot_env` so that `tinyplot_add()` layers (e.g., jitter) can align correctly.
+
+## Testing & CI
+
+Tests use `tinytest` + `tinysnapshot`. Snapshot tests produce SVG output with Liberation fonts and must be run on Linux (`options("tinysnapshot_os" = "Linux")`). For non-Linux users, we provide a dedicated `.devcontainer` for running tests via VS Code or GitHub Codespaces:
+1. Open repo in VS Code
+2. Command Palette → "Dev Containers: Reopen in Container"
+3. Dependencies install automatically
+
+Non-snapshot tests (logical assertions, error checks, etc.) run fine on any platform. Even with the devcontainer, a small number of snapshot tests (~2-3) may produce false positive failures on macOS hosts due to imperceptible rendering differences. These show up in `inst/tinytest/_tinysnapshot_review/` but the visual differences are too small to detect by eye. This is a known quirk — don't worry about these specific persistent failures. However, if you see more than ~3 snapshot failures, something real is likely broken and needs investigation.
+
+### Running Tests
+```bash
+# Via Makefile
+make testall                                          # Run all tests
+make testone testfile="inst/tinytest/test-legend.R"   # Run single test file
+
+# Via R
+tinytest::run_test_dir("inst/tinytest")
+tinytest::run_test_file("inst/tinytest/test-legend.R")
+```
+
+### Continuous Integration
+All contributions should go through a pull request. PRs against `main` automatically trigger GitHub Actions CI, which runs `R CMD check` (including the full test suite) on Ubuntu with both R-release and R-devel. Snapshot tests are included in this CI run, so even if you can't run them locally, CI will catch any regressions.
+
+### CRAN Submissions
+The test suite (snapshot SVGs in particular) adds significant size to the installed package. Tests are only intended to run locally and on CI — not on CRAN. Before a CRAN submission, uncomment the `inst/tinytest/` line in `.Rbuildignore` to exclude the test directory from the built tarball. Remember to re-comment it after submission so that CI continues to pick up the tests.
+
+### Manual Testing
+Some features require manual testing, particularly:
+- Window resize behaviour (legends, facets, layers should stay aligned)
+- Positron IDE compatibility
+- Interactive device behaviour
+
+## Development Workflow
+
+### Makefile Commands
+```bash
+make help        # Show all available commands
+make document    # Generate documentation (devtools::document)
+make check       # Full R CMD check
+make install     # Install package locally
+make website     # Build documentation website (altdoc)
+```
+
+### Adding a New Plot Type
+Where possible, reuse existing `draw_*()` and `data_*()` functions rather than writing new ones from scratch. Many types are thin wrappers that combine existing building blocks with custom data transformations. For example:
+- `type_lm`, `type_glm`, and `type_loess` all use `draw_ribbon()` — they only differ in their `data_*()` functions
+- `type_barplot` and `type_histogram` both use `draw_rect()`
+- `type_jitter` and `type_pointrange` both use `draw_points()`
+- `type_spline` and `type_summary` both use `draw_lines()`
+- `type_errorbar` reuses `data_pointrange()` entirely
+- `type_area` has no draw function at all — its data function sets `type = "ribbon"` to delegate drawing
+
+Steps:
+1. Create `R/type_<name>.R` with the `type_<name>()` constructor, `draw_<name>()`, and optionally `data_<name>()`
+2. Register the type in `R/sanitize_type.R`: add the string name to the `known_types` vector and a corresponding entry in the `switch` statement that maps it to the constructor
+3. Add `@export` tag to the constructor
+4. Run `make document` to update NAMESPACE
+5. Add tests in `inst/tinytest/test-type_<name>.R`
+6. Add snapshot SVGs by running tests on Linux (devcontainer)
+
+### Modifying Legend Behaviour
+Type-specific legend customizations should go in the type's `data` function by modifying `settings$legend_args`:
+```r
+settings$legend_args[["pch"]] = settings$legend_args[["pch"]] %||% 22
+settings$legend_args[["pt.cex"]] = settings$legend_args[["pt.cex"]] %||% 3.5
+```
+
+## Common Pitfalls
+
+- **Legend misalignment on resize**: Ensure coordinate-dependent calculations are inside `recordGraphics()`. See PRs #438, #540, #541.
+- **Layer alignment with grouped types**: When adding jitter/points on top of boxplot/violin, the layer needs access to `group_offsets` from `.tinyplot_env`. See PR #561.
+- **Theme hook corruption**: Always save and restore `before.plot.new` hooks when calling `plot.new()` in legend code.
+- **R 4.0.0 compat**: No `|>` pipe, no `\()` lambda, no `%||%` (package defines its own for R <= 4.4.0).
+
+## Links
+
+- Docs: https://grantmcdermott.com/tinyplot/
+- Issues: https://github.com/grantmcdermott/tinyplot/issues
+- CRAN: https://CRAN.R-project.org/package=tinyplot
diff --git a/.Rbuildignore b/.Rbuildignore
index 10f345fc..26a6145c 100644
--- a/.Rbuildignore
+++ b/.Rbuildignore
@@ -26,3 +26,4 @@ inst/Psychoco2026
 Makefile
 ^.devcontainer
 Rplots.pdf
+^\.CLAUDE\.md$
diff --git a/NEWS.md b/NEWS.md
index 255fc6ff..42153052 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -36,6 +36,7 @@ where the formatting is also better._
 - We now encourage type-specific legend customizations within the individual
   `type_<type>` constructors. (#531 @grantmcdermott)
 - Change maintainer email address.
+- Add `.CLAUDE.md` context file for AI-assisted development. (#563 @grantmcdermott)
 
 ### Documentation