Unified Resource-Grounded Coordination Protocol for Orchestrator-Free Heterogeneous Multi-Agent Systems

Multi-agent language-model systems typically rely on a human designer or external orchestrator to fix the agent population, roles, and workflow—a single point of failure that places coordination decisions outside the team executing them. Existing approaches address fragments of this problem: communication standards lack coordination logic, automated workflow-search systems concentrate authority in a single planner, and decentralized peers lack explicit governance, handoff validation, and bounded repair. To close this gap, we introduce the Unified Resource-Grounded Coordination Protocol (URCP), an orchestrator-free protocol in which a fixed pool of black-box models and executable resources collectively decides task framing, role formation, workflow topology, assignment, checkpoint validation, and final completion through supermajority voting under a single decision rule Φq. A five-level repair hierarchy reopens only the affected part of the workflow on failure; under standard timing and communication assumptions, every run terminates with an explicit verdict. Empirically, with twelve heterogeneous models against eight baselines on MultiAgentBench, τ-bench, MemoryAgentBench, GAIA, and REALM-Bench, URCP exceeds the strongest baseline by +9.7 / +7.9 / +10.6 points on the three primary benchmarks, terminates deadlock-free in 100% of runs, and remains stable up to 20% agent failure. Trace analyses show that the gains come from voted role concentration on frontier models (73.9% of critical-path roles), frequent critic/verifier insertion (63.5% of accepted schemas with at least three roles), and bounded repair rather than from model strength alone.