feat(FXC-5154) Warn gmsh min cylinder radii

[marc-flex]

Note

Low Risk
Adds logging-only validation warnings and a small geometry traversal tweak; no simulation behavior changes beyond additional warnings.

Overview
Adds validation-time warnings in HeatChargeSimulation when any Cylinder in structures has an effective radius below the OpenCASCADE/gmsh meshing tolerance, including checks for tapered cylinders (radius_bottom/radius_top) and nested/translated cylinders via traverse_geometries.

Extends traverse_geometries to recurse into base.Transformed geometries, and adds tests asserting the new warnings for tiny-radius cylinders and steeply-tapered cylinders that produce too-small/negative top radii.

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Greptile Overview

Greptile Summary

This PR adds validation-time warnings for HeatChargeSimulation when Cylinder geometries have radii below the minimum threshold required for gmsh/OpenCASCADE meshing. The implementation correctly traverses nested geometries and checks both tapered and non-tapered cylinders.

Key Changes:

• Added MIN_GMSH_RADIUS constant (1e-6) to define OpenCASCADE tolerance
• Implemented _warn_small_cylinder_radius validator that checks radius_bottom and radius_top against computed minimum
• Added comprehensive test coverage for both tiny-radius and steeply-tapered cylinder cases

Issues Found:

• Line 379 uses direct float equality (!=) which can be unreliable; should use tolerance-based comparison with np.isclose
• Missing CHANGELOG.md entry (required per custom rules for user-facing changes)

Confidence Score: 3/5

• Safe to merge after fixing the floating-point comparison issue and adding CHANGELOG entry
• The feature is well-tested and adds useful warnings without changing behavior. The main concern is the floating-point comparison bug on line 379 which could cause incorrect is_tapered detection in edge cases. Missing CHANGELOG is a process violation but doesn't affect code quality.
• Pay attention to tidy3d/components/tcad/simulation/heat_charge.py line 379 for the float comparison fix

Important Files Changed

Filename	Overview
tidy3d/components/tcad/simulation/heat_charge.py	Adds validator to warn about small cylinder radii; has floating-point comparison issue on line 379 that needs fixing
tests/test_components/test_heat_charge.py	Adds test coverage for small cylinder radius warnings; covers both tiny radius and tapered cylinder cases

Sequence Diagram

sequenceDiagram
    participant User
    participant HeatChargeSimulation
    participant Validator as _warn_small_cylinder_radius
    participant GeomUtils as traverse_geometries
    participant Cylinder
    participant Logger as log.warning

    User->>HeatChargeSimulation: Create simulation with structures
    HeatChargeSimulation->>Validator: Validate structures field
    
    loop For each structure
        Validator->>GeomUtils: traverse_geometries(structure.geometry)
        GeomUtils-->>Validator: Yields nested geometries
        
        loop For each geometry
            alt geometry is Cylinder
                Validator->>Cylinder: Get radius_bottom
                Cylinder-->>Validator: r_bottom
                Validator->>Cylinder: Get radius_top
                Cylinder-->>Validator: r_top
                
                Validator->>Validator: Check if tapered (r_bottom != r_top)
                Validator->>Validator: Compute min_radius = max(MIN_GMSH_RADIUS, 0.01*max(abs(r_bottom), abs(r_top)))
                
                alt is_tapered
                    alt r_bottom < min_radius
                        Validator->>Logger: Warn about radius_bottom
                    end
                    alt r_top < min_radius
                        Validator->>Logger: Warn about radius_top
                    end
                else not tapered
                    alt r_bottom < min_radius
                        Validator->>Logger: Warn about radius
                    end
                end
            end
        end
    end
    
    Validator-->>HeatChargeSimulation: Return validated structures
    HeatChargeSimulation-->>User: Simulation created (with warnings)

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Context used:

• Rule from dashboard - Use a tolerance-based comparison (e.g., np.isclose) for floating-point numbers instead of direct equ... (source)
• Rule from dashboard - Update the CHANGELOG.md file when making changes that affect user-facing functionality or fix bugs. (source)

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_{2 files reviewed, 1 comment}

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[Copilot]

Pull request overview

This pull request adds validation to warn users when cylinder radii are too small for gmsh meshing in heat-charge simulations. The feature helps prevent meshing issues by alerting users to geometries that may cause problems during the meshing process.

Changes:

• Added MIN_GMSH_RADIUS constant (1e-6) representing OpenCASCADE tolerance
• Implemented _warn_small_cylinder_radius validator that checks cylinder radii and warns when they fall below meshing thresholds
• Added comprehensive tests covering both non-tapered and tapered cylinder scenarios

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
tidy3d/components/tcad/simulation/heat_charge.py	Added imports for Cylinder and traverse_geometries, defined MIN_GMSH_RADIUS constant, and implemented validator to warn about small cylinder radii
tests/test_components/test_heat_charge.py	Added test function to verify warnings are issued for small cylinder radii in both non-tapered and tapered cases

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Diff Coverage

Diff: origin/develop...HEAD, staged and unstaged changes

• tidy3d/components/geometry/utils.py (100%)
• tidy3d/components/tcad/simulation/heat_charge.py (95.2%): Missing lines 392

Summary

• Total: 23 lines
• Missing: 1 line
• Coverage: 95%

tidy3d/components/tcad/simulation/heat_charge.py

Lines 388-396

  388 
  389                     # Warn if radii are below minimum
  390                     if is_tapered:
  391                         if r_bottom < min_radius:
! 392                             log.warning(
  393                                 f"Cylinder 'radius_bottom' ({r_bottom:.3e}) is below the minimum "
  394                                 f"radius for meshing ({min_radius:.3e}). The sidewall angle may be "
  395                                 f"too steep. Will be clamped to minimum radius or mesh size, whichever is larger."
  396                             )

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