ENH: Preserve module pyproject.toml when rewriting ITK deps

Back up pyproject.toml to pyproject.toml.orig before rewriting ITK
dependency pins, then restore the original after the wheel is built.
The modified version is saved as pyproject.toml.whl for reference.
Uses try/finally to guarantee restore even if the build fails.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: hjmjohnson

scripts/build_python_instance_base.py

@@ -772,12 +772,20 @@ def build_external_module_python_wheel(self):
         out_dir = self.module_source_dir / "dist"
         out_dir.mkdir(parents=True, exist_ok=True)
 
-        # Dynamically update ITK dependency pins to match the version being built
+        # Dynamically update ITK dependency pins to match the version being built.
+        # Back up the original pyproject.toml so the working tree is restored
+        # after the wheel is produced.
         module_pyproject = self.module_source_dir / "pyproject.toml"
+        pyproject_orig = module_pyproject.with_suffix(".toml.orig")
+        pyproject_whl = module_pyproject.with_suffix(".toml.whl")
+        deps_rewritten = False
         if module_pyproject.is_file():
             itk_ver = self.package_env_config.get("ITK_PACKAGE_VERSION", "")
             if itk_ver:
-                self._update_module_itk_deps(module_pyproject, itk_ver)
+                shutil.copy2(module_pyproject, pyproject_orig)
+                deps_rewritten = self._update_module_itk_deps(
+                    module_pyproject, itk_ver
+                )
 
         # Ensure venv tools are first in PATH
         py_exe = str(self.package_env_config["PYTHON_EXECUTABLE"])  # Python3_EXECUTABLE
@@ -875,11 +883,21 @@ def build_external_module_python_wheel(self):
         # Module source directory to build
         cmd += [self.module_source_dir]
 
-        self.echo_check_call(cmd)
+        try:
+            self.echo_check_call(cmd)
 
-        # Post-process produced wheels (e.g., delocate on macOS x86_64)
-        for wheel in out_dir.glob("*.whl"):
-            self.fixup_wheel(str(wheel), remote_module_wheel=True)
+            # Post-process produced wheels (e.g., delocate on macOS x86_64)
+            for wheel in out_dir.glob("*.whl"):
+                self.fixup_wheel(str(wheel), remote_module_wheel=True)
+        finally:
+            # Restore original pyproject.toml so the working tree stays clean
+            if deps_rewritten and pyproject_orig.is_file():
+                shutil.copy2(module_pyproject, pyproject_whl)
+                shutil.move(str(pyproject_orig), str(module_pyproject))
+                print(
+                    f"Restored {module_pyproject} "
+                    f"(modified version saved as {pyproject_whl.name})"
+                )
 
     def build_itk_python_wheels(self):
         """Build all ITK Python wheels listed in ``WHEEL_NAMES.txt``."""