Handing a task off mid-flight costs 22-34.6% of what restarting costs.

Commitment-Frontier Residual Completion formulates model-to-model handoff as commitment-constrained residual completion: freeze a residual contract from accepted progress, close the successor's continuation into an evidence-linked graph, admit execution only when the remainder is covered (arXiv 2609.13800). Across five environments and two same-provider model pairs it matches strong full-task agents on macro accuracy at 22.0% to 34.6% of inference cost, and cross-provider transfer holds. Three enforced invariants: target-before-proposal, whole-proposal-before-authority, live-evidence-before-success.