Rare State Isolation

Use this when every repeated unit carries state for comments, menus, hover chrome, debug panels, selection tools, or context actions.

Rule

The primary repeated unit should render primary content only. Rare UI state mounts only when active.

Check

• comments are indexed by location and rendered only where present
• menus/context panels mount on demand
• hover/focus tools do not add heavy props to every unit
• debug panels are outside hot unit props
• "has something here" booleans are split from heavy payload reads

Reject

• one generic unit component carrying all product state
• repeated unit props containing comment payloads, menu state, hover state, and debug state for every row/block

Use Vercel rerender-defer-reads, rerender-memo, and js-index-maps for the micro-rules. This rule owns the product-scale isolation requirement.