chore: improve support for agents

Signed-off-by: Henry Schreiner <henryfs@princeton.edu>
Assisted-by: OpenCode:Kimi-K2.5
Assisted-by: Copilot:Claude-Haiku-4.5

Author: henryiii

.github/workflows/copilot-setup-steps.yml

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+name: "Copilot Setup Steps"
+
+# Automatically run the setup steps when they are changed to allow for easy validation, and
+# allow manual testing through the repository's "Actions" tab
+on:
+  workflow_dispatch:
+  push:
+    paths:
+      - .github/workflows/copilot-setup-steps.yml
+  pull_request:
+    paths:
+      - .github/workflows/copilot-setup-steps.yml
+
+permissions: {}
+
+jobs:
+  # The job MUST be called `copilot-setup-steps` or it will not be picked up by Copilot.
+  copilot-setup-steps:
+    runs-on: ubuntu-latest
+
+    # Set the permissions to the lowest permissions possible needed for your steps.
+    # Copilot will be given its own token for its operations.
+    permissions:
+      contents: read
+
+    steps:
+      - uses: actions/checkout@v5
+
+      - name: Install system dependencies
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y \
+            doxygen \
+            clang-tidy
+
+      - name: Install pre-commit hooks
+        run: |
+          pipx install prek
+          prek install-hooks
+

AGENTS.md

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+# CLI11 Agent Guide
+
+Header-only C++11 command line parser library. CMake is the primary build
+system; Meson and Bazel are also supported.
+
+## Quick Build & Test
+
+```bash
+# Default workflow (configure + build + test)
+cmake --workflow default
+
+# Or manually
+cmake -S . -B build -DCMAKE_BUILD_TYPE=Debug
+cmake --build build -j4
+cmake --build build --target test   # or: cd build && ctest --output-on-failure
+```
+
+## Running a Single Test
+
+Tests are individual Catch2 executables in `build/tests/`.
+
+```bash
+# Run one test executable directly
+./build/tests/AppTest
+
+# Or via CTest with a regex
+ctest -R AppTest --output-on-failure
+```
+
+## Key CMake Options
+
+| Option                     | Default                 | Purpose                                 |
+| -------------------------- | ----------------------- | --------------------------------------- |
+| `CLI11_BUILD_TESTS`        | `ON` (if top-level)     | Build Catch2 test suite                 |
+| `CLI11_BUILD_EXAMPLES`     | `ON` (if top-level)     | Build `examples/`                       |
+| `CLI11_BUILD_DOCS`         | `ON` (if Doxygen found) | Build Doxygen docs                      |
+| `CLI11_SINGLE_FILE`        | `OFF`                   | Generate single `CLI11.hpp` header      |
+| `CLI11_PRECOMPILED`        | `OFF`                   | Build static lib instead of header-only |
+| `CLI11_WARNINGS_AS_ERRORS` | `OFF`                   | Turn warnings into errors               |
+| `CLI11_SANITIZERS`         | `OFF`                   | Enable ASan/TSan/UBSan                  |
+| `CLI11_BOOST`              | `OFF`                   | Enable Boost.Optional tests             |
+| `CLI11_CUDA_TESTS`         | `OFF`                   | Compile tests with NVCC                 |
+
+`CLI11_SINGLE_FILE` and `CLI11_PRECOMPILED` are mutually exclusive.
+
+## Presets
+
+- `default` — Debug, Ninja, `CLI11_WARNINGS_AS_ERRORS=ON`, export compile
+  commands.
+- `tidy` — Inherits `default`, adds `clang-tidy` with warnings-as-errors.
+
+```bash
+cmake --preset tidy
+cmake --build --preset tidy
+```
+
+## Single Header Generation
+
+Requires Python. Enable with `CLI11_SINGLE_FILE=ON`:
+
+```bash
+cmake -S . -B build -DCLI11_SINGLE_FILE=ON
+cmake --build build --target CLI11-generate-single-file
+# Output: build/single-include/CLI11.hpp
+```
+
+Script: `scripts/MakeSingleHeader.py`.
+
+## Library Structure
+
+- `include/CLI/` — Public headers. The umbrella header is `CLI.hpp`.
+- `include/CLI/impl/` — `_inl.hpp` implementation headers included by the main
+  headers.
+- `src/` — `.cpp` files used **only** when `CLI11_PRECOMPILED=ON`.
+- `single-include/` — CMake rules for the single-header build.
+- `tests/` — Catch2 tests. `main.cpp` + `catch.hpp` provide the test runner.
+- `tests/data/` — Test data files copied to the build dir automatically.
+- `examples/` — Standalone example programs.
+- `book/` — Extra documentation/examples built only when top-level.
+
+## Testing Notes
+
+- Catch2 is auto-downloaded (v2.13.10 header) if not found on the system. Both
+  Catch2 v2 and v3 are supported.
+- Some tests launch helper applications (`ensure_utf8`, `ensure_utf8_twice`)
+  built from `tests/applications/`.
+- `FuzzFailTest` requires C++17.
+- `WindowsTest` is only built on Windows.
+- `DeprecatedTest` compiles with `-Wno-deprecated-declarations`.
+- `TimerTest` is in `CLI11_MULTIONLY_TESTS` (exercises multi-threading).
+
+## Code Style & Linting
+
+Pre-commit hooks are configured in `.pre-commit-config.yaml`:
+
+- `clang-format` for C++/C/CUDA
+- `cmake-format` for CMake
+- `black` for Python
+- `prettier` for YAML/Markdown/JSON/etc.
+- `codespell` for typos
+- `markdownlint-cli2`
+- Custom checks: disallow a few common mistakes Run locally:
+
+```bash
+prek -a
+```
+
+## Version Source of Truth
+
+The version string is read from `include/CLI/Version.hpp` at configure time. Do
+not edit project version in `CMakeLists.txt`.