ENH: Branch between Strategy 3 and Strategy 1 for ITK dep resolution

When a remote module declares dynamic = ["dependencies"] in its
[project] table, skip the pyproject.toml rewrite (Strategy 1) and
instead set ITK_PACKAGE_VERSION in the environment for the
scikit-build-core metadata provider to pick up (Strategy 3).

Modules that have not yet opted into dynamic dependencies continue
to use the build-time rewrite fallback, so both approaches coexist
during the transition.

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

Author: hjmjohnson

scripts/build_python_instance_base.py

@@ -778,6 +778,32 @@ def _update_module_itk_deps(pyproject_path: Path, itk_version: str) -> bool:
         """
         import re
 
+        try:
+            import tomllib
+        except ModuleNotFoundError:
+            import tomli as tomllib  # Python < 3.11
+
+        with open(pyproject_path, "rb") as f:
+            pyproject_data = tomllib.load(f)
+
+        # --- Strategy 3: module declares dynamic dependencies -----------------
+        dynamic_fields = (
+            pyproject_data.get("project", {}).get("dynamic", [])
+        )
+        if "dependencies" in dynamic_fields:
+            # The module has opted into dynamic dependency resolution.
+            # Set ITK_PACKAGE_VERSION in the environment so the
+            # scikit-build-core metadata provider (itk-build-metadata)
+            # can emit the correct Requires-Dist at build time.
+            os.environ["ITK_PACKAGE_VERSION"] = itk_version
+            print(
+                f"Strategy 3: {pyproject_path.name} declares "
+                f"dynamic=[\"dependencies\"]; set ITK_PACKAGE_VERSION="
+                f"{itk_version} for metadata provider"
+            )
+            return False  # no file modification needed
+
+        # --- Strategy 1: build-time rewrite (fallback) ------------------------
         text = pyproject_path.read_text(encoding="utf-8")
         # Match lines like:  "itk-core == 5.4.*"  or  "itk-filtering==5.4.*"
         pattern = re.compile(
@@ -804,7 +830,7 @@ def _replace(m: re.Match) -> str:
         if changed:
             pyproject_path.write_text(new_text, encoding="utf-8")
             print(
-                f"Updated ITK dependency pins in {pyproject_path} "
+                f"Strategy 1: Updated ITK dependency pins in {pyproject_path} "
                 f"(>= {min_floor} for ITK {itk_version})"
             )
         return changed