TopoContour: Persistent-Homology-Gated Counterfactual Path Deletion for Fixed-Budget Filled SVG Repair

Repairing a filled SVG requires mapping a raster-space defect to the vector path that caused it. We introduce TopoContour, a topology-aware framework that converts unmatched PH events into path proposals and tests them through counterfactual B´ezier path deletion under a fixed geometry budget. Across synthetic data and two real filled-SVG domains, TopoContour consistently improves topology repair and path responsibility relative to residual-driven alternatives. On Tabler Filled and Bootstrap Filled, the topology-repair rate improves over residual-centered gating by 24.7 and 27.5 percentage points, respectively. Compared with exhaustive ungated search, TopoContour evaluates 47.3% and 48.0% fewer candidates while retaining 95.8% and 96.5% of its topology-repair performance. Boundary F1 remains comparable. The same pattern holds for asymmetric blobs and rounded-square B´ezier contours, with topology-repair rates between 0.894 and 0.952. Increasing the path budget from 4 to 16 raises the reduction in candidate evaluations to 86.2% on Bootstrap and 93.1% on Tabler, with counterfactual repair-decision speedups of 12.5× and 13.7×. The results show that PH events can serve as effective, transferable action proposals for efficient path-level vector repair