Design Drift
Definition
The gradual accumulation of visual and structural inconsistencies across a product's UI when multiple agents, sessions, or developers make locally reasonable design decisions that collectively diverge from the intended design system. In the agentic coding era, design drift is the visual equivalent of technical debt — each AI coding session produces working code fast, but without shared contracts the result is 5 different filter patterns, 10+ heading sizes, 8 max-widths, 3 breadcrumb formats, inconsistent sidebars, and pages that feel like different sites. Design drift is the primary failure mode when building UIs across multiple agent sessions without a machine-readable design system.
Builder Context
Design drift is inevitable in multi-session agentic builds unless you actively prevent it. The fix is structural, not procedural: ban raw values (hardcoded hex, px sizes) and enforce design tokens at the CI level. CLAUDE.md alone won't prevent drift — it's one layer (agent context) in a five-layer stack. You need: (1) tokens as source of truth, (2) machine-readable component manifests, (3) agent context files, (4) lint enforcement in CI, (5) visual regression verification. The most common symptom: pages that individually look fine but feel like different sites when you navigate between them.