Behavior Engine

The sixth of ArcFlow's seven layers. Owns declarative behaviors — programs and triggers that fire in response to graph events, execute inside the engine, and write their results back through the same Cypher surface.

A behavior is a piece of work the engine performs on the graph's behalf whenever the graph changes in a way the behavior cares about. Behaviors are how an agent encodes "when X happens, do Y" without writing an external poll loop, a webhook listener, or a sidecar worker.

What the Behavior Engine provides#

Why behaviors live in the engine#

A behavior could be an external service that subscribes to the Event Bus and posts mutations through the client SDK. That works, but it loses three properties:

• Transactional grounding. A behavior running inside the engine sees the same mutation that triggered it, in the same transaction. The result it writes commits atomically with the input that caused it.
• No round-trip. No network hop, no serialisation, no reconnect logic.
• One identity story. The program is registered against the workspace; it carries the same provenance as any other authored fact.

Behaviors are the engine's answer to "stored procedure" — typed, declarative, graph-aware.

Why this is its own layer#

The Behavior Engine is downstream of every other layer:

• It consumes deltas from the Live Surface — that is how triggers fire.
• It emits results through the Query Engine — the same Cypher surface a user writes against.
• It publishes intents through the Event Bus — other behaviors and external consumers can subscribe.
• It can invoke the Algorithm Library — CALL algo.* and CALL arcflow.* procedures.

Keeping behaviors separate from the layers they consume keeps each layer's responsibilities clean. A behavior is a composition of the lower layers' guarantees.

Why this matters for agents#

For agents, the Behavior Engine is what turns the database from a record-keeper into a participant. Examples:

• A perception arrives; a program normalises it, runs entity resolution, and writes a typed entity reference.
• A new edge appears in the call graph; a trigger fires a code-intelligence skill that updates the symbol table.
• A live view's delta indicates a fraud-ring threshold crossing; a behavior emits an intent the responder consumes.

The agent does not poll. The agent does not glue services together. The agent declares the behavior once; the engine fires it whenever the graph changes in a matching way.

See also#

• Behavior Graphs — the canonical surface reference + worked examples.
• Skills — the reusable building blocks.
• Programs — the program manifest format.
• Triggers — the extension reference.
• Relationship Skills — edge-aware skill patterns.