Scenario Engine: Event-Driven Behavior Without Autonomy
Designing Deterministic Actions on the Edge
Introduction
The Scenario Engine is where perception and identity become action. Its role is not to “think” or decide freely, but to execute predefined responses to well-defined events. By design, it prevents autonomy while enabling rich, predictable behavior. This engine ensures the assistant remains useful without becoming unsafe or opaque.
Why Event-Driven Design
Continuous decision loops are unnecessary and risky for a home assistant. An event-driven model reacts only to explicit triggers: identity resolution, speech intent, time schedules, or system states. This minimizes resource usage, reduces complexity, and guarantees traceability of actions.
Core Concepts
The Scenario Engine is built around three primitives:
– Events: signals emitted by other engines
– Conditions: checks against context and state
– Actions: deterministic outputs
No scenario may create new rules at runtime. All logic is declared ahead of time.
Event Sources
Typical events include:
– IdentityResolved(owner | guest | unknown)
– SpeechIntent(command, confidence)
– TimeEvent(schedule or interval)
– SystemEvent(startup, error, idle)
Events are immutable facts, not suggestions.
Scenario Definition
A scenario is a static rule set bound to one or more events. It defines:
– priority
– required identity type
– optional conditions
– ordered actions
Scenarios never call each other recursively. This avoids emergent behavior.
Priority and Conflict Resolution
Only one scenario may execute at a time. Priority rules are strict:
1) Owner-related scenarios override all others
2) Identity-based scenarios override time-based ones
3) Safety and system scenarios override informational ones
If no scenario matches, the system does nothing.
Actions
Actions are simple, auditable operations:
– speak text via TTS
– play a sound
– send a notification
– query information
– trigger an automation endpoint
Actions cannot modify identity, permissions, or scenario definitions.
State Management
The Scenario Engine maintains minimal state:
– current active scenario
– last executed scenario
– cooldown timers
State is transient and resettable. There is no long-term behavioral memory in this layer.
Cooldowns and Rate Limiting
To prevent repetitive behavior, scenarios may define cooldown periods. For example, a greeting scenario should not trigger repeatedly while a person remains in view. Cooldowns are enforced strictly and do not adapt dynamically.
Safety Constraints
The Scenario Engine enforces hard limits:
– no chained execution beyond a fixed depth
– no external actions without explicit allowance
– no self-modifying rules
– no learning from outcomes
This guarantees deterministic behavior.
Testing and Simulation
Scenarios must be testable without live sensors. Events can be injected manually to validate priority, conditions, and actions. This enables safe iteration and regression testing before deployment.
Failure Handling
If an action fails, the scenario terminates cleanly. Errors are logged, not retried automatically unless explicitly defined. Failure never escalates privileges or triggers fallback intelligence.
Integration with Dialogue and Automation
The Scenario Engine passes bounded context to Dialogue and Automation Engines. Those engines execute tasks but cannot alter scenario flow. Control always returns to the Scenario Engine after execution.
What Comes Next
With deterministic behavior established, the next article focuses on the Dialogue Engine: speech, intent extraction, and controlled conversational interaction without turning the assistant into an open-ended agent.
