Before changing a subsystem, an AI agent (or developer) must read the matching section and the Critical Invariants. Sections:

• System Architecture — components, services, data flow — see Signage Estimator — project README
• Calculation Lifecycle — calculation → revisions → price snapshots → technology snapshot (to be written)
• Technology Engine — Technology Editor — reference, Channel Letters — configurable product engine
• Material Selection — canonical vs supplier materials, selector/family — Supplier price-list import and matching
• Nesting Pipeline — Unified nesting workspace, Geometry import and production interpretation, Nesting performance investigation
• LED Calculation — to be written
• Deployment Runbook — Production deployment: calc.sign-expert.eu (private); production runs from the git working tree — never restart with uncommitted changes
• Critical Invariants — Product rules (permanent constraints)