| This paper presents a lightweight heuristic solver for dynamic crane scheduling under the DynStack \texttt{CraneScheduling} benchmark. The setting involves two non-passing cranes, finite-capacity stacks, and online vehicle arrivals operating under strict real-time control constraints. Prior role-based coordination methods often struggle with responsiveness, feasibility under frequent replanning, and crane interference. Our approach introduces three constant-time safeguards: (i) request-aware buffer reassignment with virtual height tracking to avoid burying demanded blocks, (ii) a feasibility swap that guarantees end-to-end crane reachability, and (iii) a precedence-preserving alternating merge that balances crane utilization while maintaining non-crossing safety. Experiments on the official CS--T--01 benchmark achieved zero delivery errors, processed all 185 feasible I/O blocks, and substantially reduced parking and service times compared to earlier role-based strategies. The solver ranked first in the GECCO 2025 DynStack competition. The results show that carefully designed deterministic heuristics can remain highly effective for real-time crane scheduling under strict online control constraints. |
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