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openspec/specs/cutout-geometry-node-efficiency/spec.md

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+# cutout-geometry-node-efficiency Specification
+
+## Purpose
+TBD - created by archiving change optimize-cutout-geometry-nodes. Update Purpose after archive.
+## Requirements
+### Requirement: Depth Cutout reuses the projected outline field
+
+`O Image Depth Cutout` SHALL calculate the POINT/BOOLEAN outline field once on the post-split, pre-projection topology and reuse it for boundary-sensitive consumers on the same topology after projection. It SHALL NOT create separate Edge Neighbors and Vertex Neighbors fields for each consumer in the same topology stage.
+
+#### Scenario: Same topology boundary consumers share the field
+
+- **WHEN** Depth Cutout builds volume fields, original boundary sampling, and boundary smoothing after depth projection
+- **THEN** these consumers read the same projected outline field, and the output geometry matches the prior implementation for zero and positive thickness
+
+#### Scenario: Topology changes still receive a fresh boundary field
+
+- **WHEN** Split Edges or boundary triangle cleanup changes topology before projection
+- **THEN** the shared outline field is evaluated after that topology change, not reused across the destructive operation
+
+### Requirement: Center field derives from shared low-frequency fields
+
+`O Image Depth Cutout` SHALL compute the smoothed depth and profile fields with the existing 256-iteration interior-weighted blur, and SHALL derive the center field as `depth_slow - profile_slow` instead of running an additional equivalent blur on `depth - profile`.
+
+#### Scenario: Center field is equivalent to the direct blur
+
+- **WHEN** Depth Cutout evaluates a Balloon input with nonzero `o_balloon` and positive Thickness
+- **THEN** the derived center values are equal to the prior direct center blur values within floating-point tolerance
+
+#### Scenario: Uniform surface keeps the same center behavior
+
+- **WHEN** Depth Cutout evaluates a zero-profile uniform surface
+- **THEN** the derived center field produces the same front and rear positions as the prior implementation
+
+### Requirement: Depth Cutout uses triangle-only strip cleanup
+
+`O Image Depth Cutout` SHALL build only the triangle strip cleanup path because its input is triangulated. It SHALL NOT construct the quad strip cleanup branch used by other depth surfaces.
+
+#### Scenario: Triangular strips are cleaned without quad nodes
+
+- **WHEN** Depth Cutout receives a triangulated cutout mesh with thin boundary strips
+- **THEN** strip faces are removed and the remaining geometry matches the prior triangle cleanup result
+
+#### Scenario: Other depth surfaces keep their existing cleanup path
+
+- **WHEN** Depth Plane or Depth Panorama evaluates a quad mesh
+- **THEN** their existing quad strip cleanup behavior is unchanged
+
+### Requirement: Zero thickness short-circuits shell construction
+
+Both `O Image Cutout` and `O Image Depth Cutout` SHALL return the original single-surface geometry when the selected thickness input is below the existing zero threshold, without evaluating shell extrusion or thickness field sampling.
+
+#### Scenario: Cutout Balloon and Shell remain single surface at zero
+
+- **WHEN** Mode is Balloon or Shell and the selected Thickness or Shell Thickness is zero
+- **THEN** the output is the original Cutout surface with no shell faces, and no thickness-related node warnings occur
+
+#### Scenario: Depth Cutout keeps the projected front at zero thickness
+
+- **WHEN** Depth Cutout has zero selected thickness
+- **THEN** the output is the projected front surface, and thickness-only fields and shell geometry are not evaluated
+
+### Requirement: Node graph optimization preserves Cutout geometry
+
+The boundary reuse, center derivation, triangle-only cleanup, and zero-thickness short-circuit SHALL NOT change the finite output geometry, face order, UVMap, or public attributes for supported Cutout and Depth Cutout combinations.
+
+#### Scenario: Representative mode and thickness matrix is equivalent
+
+- **WHEN** Cutout and Depth Cutout are evaluated with Balloon/Shell modes, zero and positive thickness, Depth Split zero and positive, and representative input shapes
+- **THEN** vertex positions and face topology are equivalent to the prior implementation within the existing test tolerance
+
+#### Scenario: High-density mesh remains closed with thickness
+
+- **WHEN** Depth Cutout uses a mesh with more than 4096 source vertices and positive thickness
+- **THEN** the thickened shell remains finite and closed with no non-manifold boundary
+