Add cutout shell and volume node assets for depth volume processing

- Implemented `cutout_shell.py` to build front normals and shell positions for balloon geometry.
- Created `cutout_volume.py` to establish smooth center fields and manage balloon surface attributes.
- Introduced `pisa_sr_export.py` for exporting PiSA-SR components with dependencies and asset finalization.

tools/node_assets/cutout_volume.py

@@ -0,0 +1,88 @@
+"""Build the smooth center field for depth volume."""
+from node_graph import edge_boundary_field
+
+
+def node(group, kind, location):
+    result = group.nodes.new(kind)
+    result.location = location
+    return result
+
+
+def shift_stage(group, previous, offset):
+    for item in group.nodes:
+        if item not in previous:
+            item.location.x += offset[0]
+            item.location.y += offset[1]
+
+
+def build_volume_fields(group, geometry, offset=(0, 0)):
+    previous = set(group.nodes)
+    boundary = edge_boundary_field(group.nodes, group.links, (0, -400))
+    store = node(group, "GeometryNodeStoreNamedAttribute", (860, 0))
+    store.domain, store.data_type = "POINT", "FLOAT"
+    store.inputs["Name"].default_value = "o_balloon_surface_rim"
+    group.links.new(geometry, store.inputs["Geometry"])
+    group.links.new(boundary, store.inputs["Value"])
+    profile = node(group, "GeometryNodeInputNamedAttribute", (860, 700))
+    profile.data_type = "FLOAT"
+    profile.inputs["Name"].default_value = "o_balloon"
+    links = group.links
+    def math(operation, a, b, location):
+        result = node(group, "ShaderNodeMath", location)
+        result.operation = operation
+        for index, value in enumerate((a, b)):
+            if isinstance(value, (int, float)):
+                result.inputs[index].default_value = value
+            else:
+                links.new(value, result.inputs[index])
+        return result.outputs[0]
+    position = node(group, "GeometryNodeInputPosition", (860, 1100))
+    axes = node(group, "ShaderNodeSeparateXYZ", (1100, 1100))
+    links.new(position.outputs[0], axes.inputs[0])
+    seed = math("SUBTRACT", axes.outputs["Z"], profile.outputs["Attribute"], (1340, 900))
+    center = node(group, "GeometryNodeStoreNamedAttribute", (1340, 0))
+    center.domain, center.data_type = "POINT", "FLOAT"
+    center.inputs["Name"].default_value = "o_balloon_surface_center"
+    links.new(store.outputs["Geometry"], center.inputs["Geometry"])
+    links.new(seed, center.inputs["Value"])
+    current = node(group, "GeometryNodeInputNamedAttribute", (1660, -330))
+    current.data_type = "FLOAT"
+    current.inputs["Name"].default_value = "o_balloon_surface_center"
+    rim = node(group, "GeometryNodeInputNamedAttribute", (1660, -660))
+    rim.data_type = "FLOAT"
+    rim.inputs["Name"].default_value = "o_balloon_surface_rim"
+    interior = math("SUBTRACT", 1, rim.outputs["Attribute"], (1890, -660))
+    blur = node(group, "GeometryNodeBlurAttribute", (2120, -330))
+    blur.data_type = "FLOAT"
+    blur.inputs["Iterations"].default_value = 256
+    links.new(current.outputs["Attribute"], blur.inputs["Value"])
+    links.new(interior, blur.inputs["Weight"])
+    update = node(group, "GeometryNodeStoreNamedAttribute", (2370, 0))
+    update.domain, update.data_type = "POINT", "FLOAT"
+    update.inputs["Name"].default_value = "o_balloon_surface_center"
+    links.new(center.outputs["Geometry"], update.inputs["Geometry"])
+    links.new(blur.outputs[0], update.inputs["Value"])
+    baseline = node(group, "GeometryNodeInputNamedAttribute", (2940, 1000))
+    baseline.data_type = "FLOAT"
+    baseline.inputs["Name"].default_value = "o_balloon_surface_center"
+    profile_end = node(group, "GeometryNodeInputNamedAttribute", (2940, 700))
+    profile_end.data_type = "FLOAT"
+    profile_end.inputs["Name"].default_value = "o_balloon"
+    position_end = node(group, "GeometryNodeInputPosition", (2940, 1360))
+    axes_end = node(group, "ShaderNodeSeparateXYZ", (3180, 1360))
+    links.new(position_end.outputs[0], axes_end.inputs[0])
+    residual = math("SUBTRACT", axes_end.outputs["Z"], baseline.outputs["Attribute"], (3420, 1000))
+    full = math("ADD", residual, profile_end.outputs["Attribute"], (3660, 1000))
+    minimum = math("MULTIPLY", profile_end.outputs["Attribute"], 0.05, (3420, 700))
+    positive = math("MAXIMUM", full, minimum, (3900, 1000))
+    control = node(group, "NodeGroupInput", (3900, 700))
+    scaled = math("MULTIPLY", positive, control.outputs["Thickness"], (4140, 1000))
+    thickness = node(group, "GeometryNodeStoreNamedAttribute", (4140, 0))
+    thickness.domain, thickness.data_type = "POINT", "FLOAT"
+    thickness.inputs["Name"].default_value = "o_balloon_surface_thickness"
+    group.links.new(update.outputs["Geometry"], thickness.inputs["Geometry"])
+    group.links.new(scaled, thickness.inputs["Value"])
+    shift_stage(group, previous, offset)
+    return thickness.outputs["Geometry"]
+
+