ArXiv: 'Dive into Claude Code' — 98.4% of a Production Agent Is Deterministic Harness, Not AI; Five Compaction Shapers Run Before Every Model Call

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VILA-Lab's systematic analysis of Claude Code's TypeScript source (arXiv 2604.14228) reveals that 98.4% of a production agent's codebase is operational infrastructure, not AI decision logic. Before every model call, five compaction shapers run sequentially (cheapest first): Budget Reduction → Snip → Microcompact → Context Collapse → Auto-Compact. The paper traces 13 design principles from 5 human values to implementation choices. Key insight: as models converge in reasoning, the harness — not the model — is the differentiator.