Preserve HSSSD PDF periodicity across multiple turns

[FlorianPfaff]

Summary

• wrap hypercylindrical subdivision grid deltas modulo 2π before conditional-component selection
• use the same shortest-arc distance convention as HypertoroidalGridDistribution
• add a focused regression for equivalent angles separated by two full turns

Bug

HypercylindricalStateSpaceSubdivisionDistribution.pdf() evaluates a periodic marginal and a grid-conditioned linear density. The periodic marginal already wraps arbitrary angles correctly, but the conditional selector computed

minimum(abs_delta**2, (2 * pi - abs_delta) ** 2)

without first reducing abs_delta modulo 2π.

That expression only represents the shortest toroidal arc while the raw difference is within one revolution. For a grid with points at 0 and π, a query at 0.1 selected the first conditional, while the equivalent query at 0.1 + 4π selected the second. The joint PDF therefore violated periodicity even though its periodic marginal did not.

Fix

Reduce absolute angular differences modulo 2π, then compute the shortest wrapped distance before selecting the nearest conditional distribution. This matches the established implementation in HypertoroidalGridDistribution.get_closest_point() and value_of_closest().

Validation

• isolated numerical reproduction confirms the pre-fix selector maps 0.1 and 0.1 + 4π to different grid indices
• the corrected selector maps both queries to the same index
• regression uses distinct Gaussian conditionals and verifies equal joint densities for those equivalent angles
• modified source and regression modules pass python -m py_compile
• branch is two commits ahead of current main, zero behind
• final diff is limited to 4 additions/5 deletions in the implementation and one 45-line regression file

The full repository test matrix is delegated to GitHub Actions.

[github-actions]

✅MegaLinter analysis: Success

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✅ PYTHON	black	1490	182	0	0	87.5s
✅ PYTHON	isort	1490	327	0	0	2.52s
✅ REPOSITORY	betterleaks	yes		no	no	1.98s
✅ REPOSITORY	checkov	yes		no	no	54.09s
✅ REPOSITORY	gitleaks	yes		no	no	14.37s
✅ REPOSITORY	git_diff	yes		no	no	0.26s
✅ REPOSITORY	secretlint	yes		no	no	63.37s
✅ REPOSITORY	syft	yes		no	no	5.49s
✅ REPOSITORY	trivy-sbom	yes		no	no	5.37s
✅ REPOSITORY	trufflehog	yes		no	no	31.1s
✅ YAML	prettier	11	0	0	0	0.68s
✅ YAML	v8r	11		0	0	10.76s
✅ YAML	yamllint	11		0	0	0.56s

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