python: build a PyPI-publishable Pyodide (PEP 783) wheel (#9891)

## Summary

z3 already builds under Pyodide (there is a `pyodide.yml` workflow and
an
`IS_PYODIDE` path in `setup.py`), but that path uses `pyodide build` and
produces
a wheel tagged `emscripten_<pyodide-version>_wasm32`, which is pinned to
a single
Pyodide release and rejected by PyPI — so today it's only usable as a CI
artifact.

[PEP 783](https://peps.python.org/pep-0783/) introduced the portable
`pyemscripten_<date>_wasm32` platform tag that **PyPI accepts** and
`micropip` can
install at runtime. This makes `z3-solver` build that wheel via
`cibuildwheel --platform pyodide`.

## Changes

- **`setup.py`** — for the emscripten target, use the wheel platform tag
that
  pyodide-build provides verbatim via `_PYTHON_HOST_PLATFORM` (e.g.
`pyemscripten_2026_0_wasm32`) instead of reconstructing an
`emscripten_*` tag.
  Falls back to the previous behaviour when that env var is absent.
- **`setup.py` / `CMakeLists.txt` / `pyproject.toml`** — switch the
Pyodide build
from JS-based exceptions (`-fexceptions`,
`-sDISABLE_EXCEPTION_CATCHING=0`) to
**native wasm exception handling** (`-fwasm-exceptions
-sSUPPORT_LONGJMP=wasm`),
matching the ABI of the Pyodide 314 / emscripten 5 main module. With the
old
flags `libz3.so` imports `invoke_*` trampolines the runtime no longer
provides,
so the wheel builds but the first `Z3_mk_config` call fails at runtime
with
  `Dynamic linking error: cannot resolve symbol invoke_vi`.
- **`pyproject.toml`** — add `[tool.cibuildwheel]` /
`[tool.pyodide.build]` so
`cibuildwheel --platform pyodide` builds and tests the wheel (`cp314`).
- **`.github/workflows/pyodide-pypi.yml`** (new) — build with
cibuildwheel and
publish to PyPI (trusted publishing) on tags. Existing `pyodide.yml`
unchanged.

## Verification

Built with `cibuildwheel 4.1.0` / `pyodide-build 0.35.0` / `emscripten
5.0.3`,
CPython 3.14 / Pyodide 314:

- Produces `z3_solver-4.17.0.0-py3-none-pyemscripten_2026_0_wasm32.whl`.
- `z3test.py` passes in the Pyodide runtime (node + wasm32).
- Installed via `micropip` and solves SMT problems both under node and
in a
  browser (`sat` with a model, `unsat` for a contradiction).

🤖 Generated with [Claude Code](https://claude.com/claude-code)
🕵️‍♂️ Reviewed by [Alcides Fonseca](https://wiki.alcidesfonseca.com)

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

.github/workflows/pyodide-pypi.yml

@@ -0,0 +1,57 @@
+name: Pyodide Wheel (PyPI)
+
+# Builds a PEP 783 `pyemscripten_*_wasm32` wheel for z3-solver using cibuildwheel
+# and publishes it to PyPI on tag pushes. Unlike the legacy pyodide.yml (which
+# uses `pyodide build` and produces a Pyodide-version-locked emscripten_* wheel
+# uploaded only as a CI artifact), this wheel is installable at runtime with
+# micropip from PyPI. See src/api/python/pyproject.toml [tool.cibuildwheel].
+
+on:
+  release:
+    types: [created]
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  build-pyodide:
+    runs-on: ubuntu-24.04
+    steps:
+      - uses: actions/checkout@v6
+
+      - name: Build Pyodide wheel
+        uses: pypa/cibuildwheel@v4.1.0
+        with:
+          # The Python bindings live in a subdirectory of the repo.
+          package-dir: src/api/python
+        env:
+          CIBW_PLATFORM: pyodide
+          # Exception/longjmp/bigint flags are declared in
+          # src/api/python/pyproject.toml ([tool.pyodide.build]) and combined
+          # with Pyodide's -fwasm-exceptions defaults. Don't set CFLAGS/CXXFLAGS
+          # here — a JS-EH -fexceptions value conflicts with the wasm-EH ABI.
+
+      - name: Store Pyodide wheel
+        uses: actions/upload-artifact@v7
+        with:
+          name: pyodide-wheel
+          path: wheelhouse/*.whl
+
+  publish:
+    name: Publish to PyPI
+    runs-on: ubuntu-24.04
+    if: startsWith(github.ref, 'refs/tags/')
+    needs: [build-pyodide]
+    environment: release
+    permissions:
+      id-token: write  # trusted publishing (OIDC), no API token needed
+    steps:
+      - name: Download Pyodide wheel
+        uses: actions/download-artifact@v8
+        with:
+          name: pyodide-wheel
+          path: dist/
+
+      - name: Publish to PyPI
+        uses: pypa/gh-action-pypi-publish@release/v1