Edges define legal movement

State transitions

An edge connects one state to another. A node result may propose a target state; only a listed edge (or allow_unlisted_transitions=True) permits the move.

Edges carry labels with a fixed priority order that drives the deterministic preferred-path router, and optional guards — callables over state that gate the edge at runtime. Guards fail closed.

from neosyntropy import Edge, FSM, node

@node(id="VerifyIdentity")
def verify_identity(ctx):
    return ctx.result()

@node(id="OutOfScope", is_fallback=True)
def out_of_scope(ctx):
    return ctx.result()

graph = FSM(
    nodes=[verify_identity, out_of_scope],
    edges=[
        Edge(source="Start", target="VerifyIdentity", label="first"),
        Edge(source="VerifyIdentity", target="End", label="complete"),
    ],
)

print(graph.allows("Start", "VerifyIdentity"))  # True

When edges are not listed

Missing edges do not skip selection. Search still finds relevant nodes; validation fail-closes unless the hop is listed or the graph explicitly allows unlisted transitions.