Current Foundation Models operate fundamentally as linear sequence generators. While effective for generalist tasks, this paradigm suffers from stochastic degradation in high-assurance engineering domains. We introduce Horizon Mode, a distributed reasoning protocol that orchestrates thousands of isolated agents via a Recursive Swarm Architecture. By decoupling reasoning time from fixed context windows, we shift the optimization target from latency to solution space coverage. The probability of maintaining a valid terminal state decays exponentially with the length of the reasoning chain. If the probability of a logic error at any node is ε, the cumulative success rate is P(success) ≈ (1-ε)^L. For a task requiring 500 steps, even with 99% accuracy per step, the success rate drops to less than 1%. Dropstone bypasses this by transitioning from Next-Token Prediction to Trajectory Search Optimization. Dropstone redefines the IDE as an intelligent runtime environment. Instead of querying a single endpoint, it instantiates a search tree across thousands of agents. We deploy up to 10,000 isolated agents within ephemeral sandboxes. Divergent Initialization generates thousands of strategic variations, exploring low-probability solution paths (P < 0.05) often pruned by standard models. Agents write, compile, fail, debug, and iterate in real-time using actual compilers. To make scaling economically viable, we treat compute as a liquid asset that flows to the most promising solution branches. Layer 1 (Scout Swarm) uses highly optimized 8B parameter models for 98% of exploration at near-zero marginal cost. Scouts tag branches with probability vectors - dead ends are marked in the shared workspace, preventing other agents from wasting compute. Layer 2 (Context Promotion) triggers when a Scout identifies a candidate solution with high confidence (P > 0.85), promoting the state to Frontier Models (Opus/GPT-4 class). On the Deep-Sec benchmark, Horizon Mode achieved: 24+ hour reasoning horizons (vs. <1 hour for zero-shot), 1.4% hallucination rate (vs. 14.2% baseline), and 0.2% safety violations (vs. 3.8% baseline). The Flash-Gated Consensus Protocol reduced safety violations by 89% compared to zero-shot baselines while enabling continuous operation over multi-day engineering tasks. Horizon Mode represents a paradigm shift in automated reasoning. The synergy between the Budget-Aware Swarm and the Flash-Gated Consensus Protocol creates a system that is economically viable and probabilistically superior to linear reasoning methods. This architecture enables Dropstone to tackle complex engineering projects that require sustained reasoning over days, not hours.