Material insertion and filtered inspection

material(insert_expression_between) inserts a node into a wire without discarding its previous source output or channel masks:

{
  "action": "insert_expression_between",
  "materialPath": "/Game/Materials/M_Master",
  "targetExpression": "MakeMaterialAttributes_0",
  "targetInput": "BaseColor",
  "expressionType": "Multiply",
  "inputForUpstream": "A",
  "properties": {"ConstB": 0.5}
}

Pass exactly one of targetExpression or property. Expression inputs accept names or indices, including MakeMaterialAttributes and SetMaterialAttributes attribute names with compact or spaced spelling (BaseColor or Base Color). A material property can be BaseColor, Roughness, MaterialAttributes, or another supported property. targetInput and inputForUpstream default to the first input. The new node uses output zero. An unconnected target produces a new node with an unconnected upstream input. Properties must be editable reflected fields and are validated before mutation.

The result includes expressionName, previousSource and a rollback record. Replaying the same target, type and upstream input returns existed while the inserted node still feeds that target. Use a separate explicit graph edit if another node of the same type is needed in that location. The insertion and its inverse dirty the material; save it explicitly when ready.

material(restore_expression_insertion) accepts the rollback record's parameters, restores the original output and channel masks, and removes the inserted node. It refuses if another edit replaced the target wire, if the source was removed, or if another wire now uses the inserted node. Repeating a completed removal reports alreadyDeleted.

material(read_summary, materialPath=...) always returns expressionCount and countsByClass. Without filters, nodes is empty. classes selects full class names or short names such as Multiply; parameterNames selects parameter names. When both are supplied, both must match. Selected rows carry expressionName, class, parameterName and group.

Use propertyChain: ("property":"MaterialAttributes","depthLimit":8) to trace one material property, or propertyChain: ("targetExpression":"MakeMaterialAttributes_0","targetInput":"BaseColor","depthLimit":4) to trace a specific attributes input. The source starts at depth zero. Each node lists its input names, source outputs and masks. The read reports truncated when the depth limit (0-64, default 8) or the 2000 node cap cuts the chain short. Shared nodes and cycles are visited once. Reads do not create an editor graph, dirty the material, or save a package.