feat(lumerical): add LayerStack sidewall angles

[joamatab]

Summary

• use Lumerical Layer Builder for LayerStack layers with a nonzero sidewall angle
• map gdsfactory’s normal-relative sidewall angle to Lumerical’s vertical-relative convention
• retain GDS import for layers with vertical sidewalls

Validation

• uv run pytest gplugins/lumerical/tests/test_write_sparameters_lumerical.py gplugins/lumerical/tests/test_background_layers.py gplugins/lumerical/tests/test_netlist.py gplugins/lumerical/tests/test_netlist_get_routes.py -q
• uv run ruff check gplugins/lumerical/write_sparameters_lumerical.py gplugins/lumerical/tests/test_write_sparameters_lumerical.py

Summary by Sourcery

Support sidewall angles in Lumerical exports by using Layer Builder for non-vertical LayerStack layers while retaining GDS import for vertical layers.

New Features:

• Handle LayerStack layers with nonzero sidewall angles in Lumerical via Layer Builder and map sidewall angle conventions between gdsfactory and Lumerical.

Enhancements:

• Require material database names when using Layer Builder sidewall angles to prevent invalid configurations.

Tests:

• Extend Lumerical S-parameters tests to cover use of Layer Builder for layers with sidewall angles and verify correct sidewall angle mapping.

[sourcery-ai]

Reviewer's Guide

This PR updates the Lumerical s-parameters writer to use the Layer Builder for layers with nonzero sidewall angles while keeping the existing GDS import path for vertical sidewalls, and adds tests to validate the sidewall angle mapping and Layer Builder behavior.

Sequence diagram for Layer Builder vs GDS import in write_sparameters_lumerical

sequenceDiagram
    participant write_sparameters_lumerical
    participant LayerStack
    participant LumericalSession_s

    write_sparameters_lumerical->>LayerStack: iterate layers
    loop for each level in layer_stack.layers.values
        write_sparameters_lumerical->>LayerStack: get level.sidewall_angle
        alt level.sidewall_angle is nonzero
            write_sparameters_lumerical->>LumericalSession_s: addlayerbuilder()
            write_sparameters_lumerical->>LumericalSession_s: set(name = gplugins_layer_builder)
            write_sparameters_lumerical->>LumericalSession_s: loadgdsfile(gdspath)
            write_sparameters_lumerical->>LumericalSession_s: addlayer(layer_layer_tuple)
            write_sparameters_lumerical->>LumericalSession_s: setlayer(layer_layer_tuple, "layer number", layer_tuple)
            write_sparameters_lumerical->>LumericalSession_s: setlayer(layer_layer_tuple, "start position", zmin)
            write_sparameters_lumerical->>LumericalSession_s: setlayer(layer_layer_tuple, "thickness", thickness)
            write_sparameters_lumerical->>LumericalSession_s: setlayer(layer_layer_tuple, "sidewall angle", 90 - level.sidewall_angle)
            write_sparameters_lumerical->>LumericalSession_s: setlayer(layer_layer_tuple, "pattern material", material)
        else level.sidewall_angle is zero
            write_sparameters_lumerical->>LumericalSession_s: gdsimport(gdspath, "top", layer_tuple)
            write_sparameters_lumerical->>LumericalSession_s: setnamed(GDS_LAYER_layer_tuple, "z", z)
            write_sparameters_lumerical->>LumericalSession_s: setnamed(GDS_LAYER_layer_tuple, "z span", thickness)
            write_sparameters_lumerical->>LumericalSession_s: set_material(session = s, structure = GDS_LAYER_layer_tuple, material = material)
        end
    end

Loading

File-Level Changes

Change	Details	Files
Use Lumerical Layer Builder for non-vertical sidewall layers and keep GDS import for vertical layers.	Introduce layer_builder_name and has_layer_builder flags to manage a single Layer Builder instance per export. For levels with sidewall_angle set, create and configure a Layer Builder: addlayerbuilder, name it, and load the GDS file once. For sidewall layers, add a Layer Builder layer, set layer number, start position, thickness, and convert gdsfactory’s sidewall_angle (normal-relative) to Lumerical’s vertical-relative convention via 90 - sidewall_angle. Require material to be a string (database name) for Layer Builder usage and raise a ValueError otherwise. Retain the previous gdsimport-based path unchanged for layers with zero sidewall_angle, including z and z span settings and material assignment.	gplugins/lumerical/write_sparameters_lumerical.py
Extend the Lumerical session test double and add a test to validate Layer Builder sidewall angle handling.	Add layer_settings storage on the _Session test double to record setlayer calls. Stub out addlayerbuilder, set, loadgdsfile, addlayer, and implement setlayer to append arguments to layer_settings in the _Session class. Add a test that builds a LayerStack with a nonzero sidewall_angle, runs write_sparameters_lumerical, and asserts the Layer Builder sidewall angle is mapped to 90 - sidewall_angle (i.e., 80 degrees for 10-degree input).	gplugins/lumerical/tests/test_write_sparameters_lumerical.py

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[github-actions]

Label error. Requires at least 1 of: breaking, bug, github_actions, documentation, dependencies, enhancement, feature, maintenance, security. Found:

[sourcery-ai]

Hey - I've found 1 issue, and left some high level feedback:

• The if level.sidewall_angle: check will skip using the layer builder when sidewall_angle is 0 but also if it is None; consider explicitly distinguishing between None and numeric values to avoid surprises if sidewall_angle=0.0 is ever meaningful.
• The material type validation for sidewall-angle layers is done inside the loop; if non-string materials are allowed elsewhere, it might be clearer to validate or convert materials before this branch so the behaviour is consistent across layer types.
• The layer_builder_name constant is set but only used in a single set call; consider inlining it or moving it to a shared constant if it needs to be reused/configured in other places.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- The `if level.sidewall_angle:` check will skip using the layer builder when `sidewall_angle` is 0 but also if it is `None`; consider explicitly distinguishing between `None` and numeric values to avoid surprises if `sidewall_angle=0.0` is ever meaningful.
- The material type validation for sidewall-angle layers is done inside the loop; if non-string materials are allowed elsewhere, it might be clearer to validate or convert materials before this branch so the behaviour is consistent across layer types.
- The `layer_builder_name` constant is set but only used in a single `set` call; consider inlining it or moving it to a shared constant if it needs to be reused/configured in other places.

## Individual Comments

### Comment 1
<location path="gplugins/lumerical/write_sparameters_lumerical.py" line_range="521-526" />
<code_context>
+                s.setlayer(layername, "start position", zmin * 1e-6)
+                s.setlayer(layername, "thickness", thickness * 1e-6)
+                s.setlayer(layername, "sidewall angle", 90 - level.sidewall_angle)
+                if not isinstance(material, str):
+                    raise ValueError(
+                        "Layer Builder sidewall angles require a material database name. "
+                        f"Got {material!r} for layer {layer_tuple}."
+                    )
+                s.setlayer(layername, "pattern material", material)
+            else:
+                s.gdsimport(str(gdspath), "top", f"{layer_tuple[0]}:{layer_tuple[1]}")
</code_context>
<issue_to_address>
**issue (bug_risk):** Material handling diverges between sidewall and non-sidewall paths and may break non-string material usages.

In the previous flow, `set_material` accepted various material representations for all layers. In the sidewall-angle branch you now enforce `material` to be a string and skip `set_material`, which will raise for existing callers that pass non-string materials that were previously valid. It also introduces inconsistent type requirements between sidewall and non-sidewall paths. Please either normalize `material` to a string earlier and continue using `set_material`, or otherwise ensure both paths accept the same material types and follow a single configuration mechanism.
</issue_to_address>

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[sourcery-ai]

issue (bug_risk): Material handling diverges between sidewall and non-sidewall paths and may break non-string material usages.

In the previous flow, set_material accepted various material representations for all layers. In the sidewall-angle branch you now enforce material to be a string and skip set_material, which will raise for existing callers that pass non-string materials that were previously valid. It also introduces inconsistent type requirements between sidewall and non-sidewall paths. Please either normalize material to a string earlier and continue using set_material, or otherwise ensure both paths accept the same material types and follow a single configuration mechanism.