Merge pull request #24 from vyos/T8595-add-claude-md

general: T8595: add CLAUDE.md

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diff --git a/.github/copilot-instructions.md b/.github/copilot-instructions.md
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+../CLAUDE.md
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diff --git a/AGENTS.md b/AGENTS.md
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+CLAUDE.md
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+# CLAUDE.md
+
+## Project purpose
+
+C utility for IPv4/IPv6 address and prefix validation in shell scripts. Used by VyOS as the canonical "is this string a valid IP / network / host / CIDR?" checker invoked from XML validators and conf-mode scripts. Fast and exit-status-driven (intended for `if ipaddrcheck --is-ipv4 ...; then ...`).
+
+## Tech stack
+
+- C, autotools (`configure.ac`, `Makefile.am`, autoconf 2.x).
+- Dependencies: `libcidr` (parsing), `libpcre2-8` (regex), `check >= 0.9.4` (test framework).
+- Debian packaging under `debian/`. Upstream autotools version `1.1` (`configure.ac`); current Debian package version `1.4` (`debian/changelog`).
+
+## Build / test / run
+
+```
+autoreconf -fi          # generate configure
+./configure
+make
+make check              # uses libcheck unit tests under tests/
+make install            # installs into AC_PREFIX_DEFAULT (/usr)
+# Debian package
+dpkg-buildpackage -uc -us -tc -b
+```
+
+## Repository layout
+
+- `src/` — C sources (`ipaddrcheck.c`, headers, autotools `Makefile.am`).
+- `tests/` — libcheck C unit tests (`check_ipaddrcheck.c`) and shell integration tests (`assert.sh`, `integration_tests.sh`).
+- `man/` — manpages.
+- `debian/` — Debian packaging.
+- `configure.ac`, `Makefile.am`, `INSTALL`, `NEWS`, `ChangeLog`, `AUTHORS`, `COPYING` (GPL-2), `COPYING-LGPL` (LGPL-2.1).
+
+## Cross-repo context
+
+One of the canonical 14 VyOS-image build packages, listed in `VyOS-Networks/vyos-build-packages/repos.toml`. Built into VyOS images by `vyos-build` and invoked at runtime by `vyos-1x` validators and conf-mode scripts. Sits in the §3.5 native-libraries category alongside `hvinfo`, `udp-broadcast-relay`, etc.
+
+## Conventions
+
+- Commit / PR title format: `component: T12345: description` (Phorge task ID at https://vyos.dev mandatory). Enforced by `vyos/.github` reusable workflows where consumed.
+- Branch model: `current` (rolling), `circinus` (1.5 LTS), `sagitta` (1.4 LTS), `equuleus` (1.3 LTS).
+- Maintained by the VyOS team (`maintainers@vyos.net`); license is GPL-2 + LGPL-2.1 dual.
+
+## Mirror relationship
+
+Mirror twin: `VyOS-Networks/ipaddrcheck`. Canonical side is **here** (`vyos/ipaddrcheck`).
+
+## Notes for future contributors
+
+- Used as a CLI-level validator — exit status 0/1 is the contract. Don't break stdout/stderr conventions or add chatty output.
+- `libcidr` is by Matthew Fuller (http://www.over-yonder.net/~fullermd/projects/libcidr) — Debian-packaged.
+- Adding a new flag: extend `src/ipaddrcheck.c`'s argument table and add a libcheck test under `tests/`.