ADR A-08: Behaviour four-tier model

Status

Accepted

Context

Behaviour must distinguish what is declared from what occurred, what was executed, and what current state records exist. Collapsing those layers makes causality, replay, and invalidation ambiguous.

Decision

Behaviour uses four mutually distinct semantic tiers:

1. Declaration — state spaces, states, transitions, triggers, guards, effects, allowance definitions, policies.
2. Occurrence — stimuli or facts observed that may satisfy trigger conditions.
3. Execution — evaluated transition executions and effect applications.
4. State record — durable occupancy or allowance-account state after execution.

No class serves more than one tier.

Consequences

• State replay and invalidation can distinguish authored mechanism from observed runtime facts.
• Shapes can check tier separation directly.
• Gate 3 fixtures can test execution without confusing authored transition design with executed history.