Compatibility with numpy 2 (#764)

* binder link fixes

* Update pixi.toml for np 1 and 2

Quick overview of numpy 2 and 1 changes

- Numpy C-API dispatch table use changed.
- SWIG files rejigged for change C-API.
- data "lock" flag implemented as flags.writeable is no longer in np2
- Changes to float() and int().
- pixi.toml changes to run np2. Badlands is only np1 now so full testing
  with it can only happen once badlands np2 is release.

* Sending _rebuild_solver = True for init_temp in UWGeodynamics

If the temperature fields, BCs, solver are initialised after the
`Model.solver` then stale temperature fields can be used.
This change prevents this occurring.

* Disable ucx comms in conda-build-test.yml

UCX isn't offered as a communication style for github runners. So it's disabled at test runtime..

* update conda dir

- update the environment.yml to reference a new definitions taken from
pixi. ie `pixi project export conda-environment > environment.yml`

- remove obsolete bits for the conda build definitions.

* Update README

* add dockerignore to minimise the binder build size

* Adding AGENTS.md

* Update Changelog

* Update CHANGELOG for release 2.18.0

Updated changelog for release 2.18.0 with new features, changes, and fixes.

Author: julesghub

AGENTS.md

@@ -0,0 +1,39 @@
+# AGENTS.md — Underworld2
+
+## Setup & build
+
+- **Python**: >=3.9,<3.13 (conda build pins to <3.12). **numpy <2** required.
+- **Env manager**: pixi (`pixi.toml` at root). Commands: `pixi install` → `pixi run build` → `pixi run test`.
+- **C/C++ build** requires: PETSc (found via `pkg-config`; set `PETSC_DIR`), MPI compilers (`MPICC`, `MPICXX`, `MPIF90`), SWIG >=4.0, CMake >=4.0, Ninja, libxml2, MPI-enabled h5py (`h5py=*=mpi*`).
+- **Install**: `pip install .` or `pip install . --no-build-isolation` (CI style). Pass CMake options via `python setup.py build_ext -D"FOO=BAR"`.
+- **Clean**: `bash clean.sh` (removes build artifacts, compiled `.so`, `_uwid.py`, caches).
+
+## Tests
+
+- **Run all**: `pytest ./docs/pytests/tests.py ./docs/pytests/test_examples.py ./docs/pytests/test_user_guide.py ./docs/pytests/test_UWGeo_examples.py ./docs/pytests/test_UWGeo_tutorial11.py`
+- **CI subset** (fastest check): `pytest ./docs/pytests/tests.py ./docs/pytests/test_examples.py ./docs/pytests/test_UWGeo_examples.py`
+- All test runners use `subprocess` to execute `.py` or `.ipynb` files. Notebooks are run via `pytest --nbmake`.
+- Test notebooks live in `docs/test/`, `docs/examples/`, `docs/user_guide/`, `docs/UWGeodynamics/examples/`, `docs/UWGeodynamics/tutorials/`.
+
+## Package structure
+
+| Path | Role |
+|---|---|
+| `src/underworld/` | Main Python package (set `package_dir={"":"src"}` in setup.py) |
+| `src/underworld/libUnderworld/` | C/C++ core + SWIG wrappers, built via CMake |
+| `src/underworld/UWGeodynamics/` | High-level geodynamics API |
+| `src/underworld/visualisation/` | LavaVu-based viz |
+
+## Critical quirks
+
+1. **dlopen flags**: `__init__.py` sets `RTLD_GLOBAL` before importing `.so` modules. This must happen early — do not reorder imports.
+2. **h5py first**: h5py is imported before anything else to avoid HDF5 library conflicts with PETSc.
+3. **`_uwid.py`**: Auto-generated on first install if missing (random UUID for usage metrics). Safe to delete/recreate.
+4. **Usage metrics**: Opt out via `UW_NO_USAGE_METRICS` env var. In MPI, only rank 0 sends data.
+5. **MPI exception handling**: In multi-process runs, exceptions are caught and broadcast via barrier. Set `UW_ALL_MESSAGES` to see all ranks' tracebacks.
+6. **PRs**: Target `development` branch. Must update `CHANGELOG.md` and docstrings. See `CONTRIBUTING.rst`.
+
+## Docs
+
+- ReadTheDocs: https://underworld2.readthedocs.io (Sphinx config at `docs/development/docs_generator/conf.py`).
+- Build docs via `docs/development/docs_generator/requirements.txt` deps.

CHANGELOG.md

@@ -1,6 +1,19 @@
 CHANGELOG: Underworld2
 =======================
 
+Release 2.18.0 [2026-06-29]
+-------------------------
+New:
+* `numpy 2` and `numpy 1` compatibility, default is `numpy 1`. Badlands yet to support `numpy 2` #764
+* Enabling `pixi` package management #0fe4355 
+
+Changes:
+* github action workflow package updates, `dependabot.yml` included for future.
+* `conda/environment.yml` updated, no longer source of truth in CI testing, move to pixi instead.
+
+Fixes:
+* Fix for UWGeo losing BCs and unknown field. #762
+
 Release 2.17.3 [2026-05-14]
 ---------------------------
 New: