Import direction
Arrows point in a permitted direction: entrypoints/ → app/ → domains/* →
domains/common/, plus app/bootstrap → adapters/. A slice may import a sibling slice’s
public API directly. Only the composition root imports concrete adapters, and nothing imports
entrypoints/.
Crust integrity
External consumers use a slice’s public seam in the language’s native form — exported
identifiers, a package __init__, an index module. Internals can be renamed, split, or
reorganized freely.
Model purity
Domain code imports stdlib, common/, and sibling public APIs. Infrastructure hides behind
ports the domain defines and adapters implement.
Growth justification
Add directories and abstractions only after demonstrated pressure. Two concrete consumers are normal evidence, not a hard requirement; cycle-breaking dispatch and positional privacy are canonical examples of pressure with one consumer.
Event usage
Events resolve reverse dependencies — B reacts to A without A knowing B. They are not general-purpose messaging.
Demonstrated pressure, not a numeric count, justifies new directories and abstractions. Two concrete consumers are the normal evidence threshold, not a hard requirement. A cycle-breaking event dispatcher and a one-file positional crust are canonical examples of pressure that can justify structure with one consumer.