Validate and copy cost adjustment result matrices

[FlorianPfaff]

Summary

• validate CostMatrixAdjustmentResult.adjusted_cost_matrix during direct construction
• copy the validated matrix into result-owned storage
• add focused regressions for caller-side mutation and invalid direct inputs

Root cause

CostMatrixAdjustmentResult is a frozen dataclass, but its __post_init__() only normalized diagnostics. The matrix field was stored exactly as supplied. A caller-owned NumPy array could therefore be mutated after construction and silently change an existing result. Direct construction also bypassed the cost-matrix validation used by the adjustment application helpers, allowing one-dimensional, NaN, negative-infinity, boolean, or complex matrices into the public result container.

Fix

Normalize the matrix through the existing _as_cost_matrix() validation path and store an owned copy in __post_init__(). This aligns direct construction with matrices returned through apply_cost_matrix_adjustment() while preserving valid positive-infinity entries.

Validation

• reproduced caller-side mutation of the stored matrix before the fix
• verified the result remains unchanged after mutating the original array
• verified invalid direct constructions now raise ValueError
• isolated focused validation passed locally
• branch is two commits ahead of main, zero behind, and changes only the result container plus one regression file

The full repository test matrix is delegated to GitHub Actions.

[github-actions]

✅MegaLinter analysis: Success

Descriptor	Linter	Files	Fixed	Errors	Warnings	Elapsed time
✅ COPYPASTE	jscpd	yes		no	no	24.22s
✅ JSON	prettier	7	0	0	0	1.13s
✅ JSON	v8r	7		0	0	4.38s
✅ MARKDOWN	markdownlint	68	0	0	0	1.74s
✅ MARKDOWN	markdown-table-formatter	68	0	0	0	0.41s
✅ PYTHON	black	1490	182	0	0	96.74s
✅ PYTHON	isort	1490	328	0	0	2.68s
✅ REPOSITORY	betterleaks	yes		no	no	2.53s
✅ REPOSITORY	checkov	yes		no	no	56.58s
✅ REPOSITORY	gitleaks	yes		no	no	14.04s
✅ REPOSITORY	git_diff	yes		no	no	0.32s
✅ REPOSITORY	secretlint	yes		no	no	62.79s
✅ REPOSITORY	syft	yes		no	no	6.58s
✅ REPOSITORY	trivy-sbom	yes		no	no	6.69s
✅ REPOSITORY	trufflehog	yes		no	no	31.76s
✅ YAML	prettier	11	0	0	0	0.78s
✅ YAML	v8r	11		0	0	12.49s
✅ YAML	yamllint	11		0	0	0.63s

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