Another approach to use zig build with setuptools.

build_backend.py

@@ -37,10 +37,30 @@ def _build_libaegis():
 
 
 # Expose all the standard build backend hooks
-get_requires_for_build_wheel = _orig.get_requires_for_build_wheel
-get_requires_for_build_sdist = _orig.get_requires_for_build_sdist
-prepare_metadata_for_build_wheel = _orig.prepare_metadata_for_build_wheel
-build_sdist = _orig.build_sdist
+def get_requires_for_build_wheel(config_settings=None):
+    """Return build requirements and ensure libaegis is built first."""
+    _build_libaegis()
+    return _orig.get_requires_for_build_wheel(config_settings)
+
+
+def get_requires_for_build_sdist(config_settings=None):
+    """Return build requirements for sdist and ensure libaegis is built first."""
+    _build_libaegis()
+    return _orig.get_requires_for_build_sdist(config_settings)
+_orig_prepare_metadata_for_build_wheel = _orig.prepare_metadata_for_build_wheel
+_orig_build_sdist = _orig.build_sdist
+
+
+def prepare_metadata_for_build_wheel(metadata_directory, config_settings=None):
+    """Prepare metadata and ensure libaegis is built (some frontends call this early)."""
+    _build_libaegis()
+    return _orig_prepare_metadata_for_build_wheel(metadata_directory, config_settings)
+
+
+def build_sdist(sdist_directory, config_settings=None):
+    """Build sdist, building libaegis first so the sdist can include built artifacts if needed."""
+    _build_libaegis()
+    return _orig_build_sdist(sdist_directory, config_settings)
 
 
 def build_wheel(wheel_directory, config_settings=None, metadata_directory=None):

pyproject.toml

@@ -12,7 +12,6 @@ classifiers = [
   "Programming Language :: Python :: 3",
   "Programming Language :: Python :: 3 :: Only",
   "Programming Language :: Python :: Implementation :: CPython",
-  "License :: OSI Approved :: ISC License (ISCL)",
   "Operating System :: OS Independent",
   "Topic :: Security :: Cryptography",
 ]

setup.py

@@ -5,6 +5,28 @@ from pathlib import Path
 from cffi import FFI
 from setuptools import setup
 
+
+def find_libaegis():
+    """Locate libaegis.a - check common locations."""
+    libaegis_paths = [
+        Path("libaegis/zig-out/lib/libaegis.a"),  # Zig build output (repo build)
+        Path("libaegis/build/libaegis.a"),  # CMake build output (repo build)
+        Path("../libaegis/zig-out/lib/libaegis.a"),  # When building from extracted sdist
+        Path("../libaegis/build/libaegis.a"),  # When building from extracted sdist
+        Path("/usr/local/lib/libaegis.a"),  # System install
+        Path("/usr/lib/libaegis.a"),  # System install
+    ]
+
+    for path in libaegis_paths:
+        if path.exists():
+            print(f"Found libaegis.a at: {path.resolve()}")
+            return str(path.resolve())
+    
+    # Return None instead of raising - will be caught during build
+    return None
+
+
+# Read the CDEF header
 cdef_path = Path(__file__).parent / "pyaegis" / "aegis_cdef.h"
 cdef_content = cdef_path.read_text(encoding="utf-8")
 
@@ -12,37 +34,16 @@ cdef_content = cdef_path.read_text(encoding="utf-8")
 ffibuilder = FFI()
 ffibuilder.cdef(cdef_content)
 
-# Locate libaegis.a - check common locations
-libaegis_paths = [
-    Path("libaegis/zig-out/lib/libaegis.a"),  # Zig build output (repo build)
-    Path("libaegis/build/libaegis.a"),  # CMake build output (repo build)
-    Path("../libaegis/zig-out/lib/libaegis.a"),  # When building from extracted sdist
-    Path("../libaegis/build/libaegis.a"),  # When building from extracted sdist
-    Path("/usr/local/lib/libaegis.a"),  # System install
-    Path("/usr/lib/libaegis.a"),  # System install
-]
-
-libaegis_static = None
-for path in libaegis_paths:
-    if path.exists():
-        libaegis_static = path.resolve()
-        print(f"Found libaegis.a at: {libaegis_static}")
-        break
-
-if not libaegis_static:
-    raise FileNotFoundError(
-        "libaegis.a not found. Please build libaegis first. "
-        f"Searched: {[str(p) for p in libaegis_paths]}"
-    )
-
 # Include directory for headers
 include_dirs = []
 libaegis_include = Path("libaegis/src/include")
 if libaegis_include.exists():
     include_dirs.append(str(libaegis_include.resolve()))
 
-# Set the source - we don't need any C source files since we're linking to the static library
-# CFFI will generate the wrapper code automatically
+# Try to find libaegis.a, but don't fail if not found (build backend will build it)
+libaegis_static = find_libaegis()
+
+# Set the source
 ffibuilder.set_source(
     "pyaegis._aegis",  # module name
     """
@@ -55,7 +56,7 @@ ffibuilder.set_source(
     #include "aegis256x4.h"
     """,
     include_dirs=include_dirs,
-    extra_objects=[str(libaegis_static)],  # Link against the static library
+    extra_objects=[libaegis_static] if libaegis_static else [],
 )
 
 if __name__ == "__main__":