fix(lumerical): extend ports beyond PML

[joamatab]

Summary

• include per-side FDTD margins in the physical port extension length
• ensure exported waveguides extend beyond the PML for every port orientation
• add a regression test comparing exported GDS and FDTD bounds

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
• uv run ruff format --check gplugins/lumerical/write_sparameters_lumerical.py gplugins/lumerical/tests/test_write_sparameters_lumerical.py

Summary by Sourcery

Extend exported waveguides so that all ports reach beyond the FDTD PML margins and add coverage via regression testing.

Bug Fixes:

• Ensure physical port extensions include per-side FDTD margins so exported waveguides reach beyond the PML for all port orientations.

Tests:

• Add a regression test verifying that the exported GDS geometry extends beyond the simulated FDTD bounds for configured margins.

[sourcery-ai]

Reviewer's Guide

Extends physical port waveguides so they reach beyond the FDTD PML margins and adds a regression test to verify exported GDS bounds against FDTD simulation bounds, using a more stateful test session stub to capture FDTD and GDS settings.

Sequence diagram for updated port extension beyond PML in write_sparameters_lumerical

sequenceDiagram
    participant write_sparameters_lumerical
    participant extension_extend_ports

    write_sparameters_lumerical->write_sparameters_lumerical: [compute port_extension_beyond_pml from ss.port_extension and xmargin_left/xmargin_right/ymargin_top/ymargin_bot]
    write_sparameters_lumerical->extension_extend_ports: extend_ports(component_extended, port_extension_beyond_pml)
    extension_extend_ports-->write_sparameters_lumerical: component_extended_beyond_pml

Loading

File-Level Changes

Change	Details	Files
Extend physical port waveguides beyond the FDTD PML margins when writing Lumerical S-parameters.	Compute an effective port extension that includes both the configured port_extension and the maximum of per-side FDTD margins. Use the combined extension length when generating the component with extended ports so waveguides always extend beyond the PML regardless of port orientation. Preserve existing behavior of flattening the extended component after adjusting the extension length.	gplugins/lumerical/write_sparameters_lumerical.py
Enhance the Lumerical write_sparameters tests with a stateful session stub and a regression test ensuring exported GDS extends beyond FDTD bounds.	Update the _Session test double to record FDTD solver settings passed to addfdtd and the path used for GDS import. Add a regression test that writes S-parameters for a simple straight waveguide and then re-imports the exported GDS to compare its x-bounds against recorded FDTD x_min/x_max. Validate that the exported component’s x-range exceeds the FDTD bounds in both directions, confirming ports extend beyond PML with margins applied.	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 left some high level feedback:

• In port_extension_beyond_pml, using max(xmargin_left, xmargin_right, ymargin_top, ymargin_bot) assumes symmetric behavior across all orientations; if margins are intentionally asymmetric per side, consider computing the required extension per port direction instead of a global max to avoid over-extension on some ports.
• In test_port_extension_reaches_beyond_pml, relying on re-importing the written GDS path adds I/O and an extra dependency on the GDS import behavior; consider asserting against the bounds of component_extended_beyond_pml (or the object passed to gdsimport) directly via a hook or helper to keep the test focused on the FDTD/port extension logic.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- In `port_extension_beyond_pml`, using `max(xmargin_left, xmargin_right, ymargin_top, ymargin_bot)` assumes symmetric behavior across all orientations; if margins are intentionally asymmetric per side, consider computing the required extension per port direction instead of a global max to avoid over-extension on some ports.
- In `test_port_extension_reaches_beyond_pml`, relying on re-importing the written GDS path adds I/O and an extra dependency on the GDS import behavior; consider asserting against the bounds of `component_extended_beyond_pml` (or the object passed to `gdsimport`) directly via a hook or helper to keep the test focused on the FDTD/port extension logic.

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