---
id: BR-6
family: RT-BR
level: core
profiles: [runtime]
posture: normative-target
added: "1.0"
changed: "1.0"
source: https://flowdrop.io/spec/rules/rt-br/br-6
specification: FlowDrop Workflow Specification 1.0-draft
licence: CC BY 4.0
---

# BR-6 — A stale source does not satisfy an edge

*RT-BR (Part II) · level: core · profiles: runtime · added in 1.0*

Inside a loop, a source can be completed and branch-active and still be speaking for the wrong round. Two independent staleness tests sit on every edge, and a source gated by either does not satisfy.

## The rule

> **Normative.** This is the rule.
>
> 1. A source that has been superseded does not satisfy an edge: where a newer execution of the source node already exists, that source's branch decision must not activate a trigger edge, an error edge, or a data edge leaving a named port of a source that emitted an active-branch list; a source vouches only for its own iteration.
>
> 2. Independently, a completed source from a round behind the consumer's, on a loop both are inside, does not satisfy a trigger, error or ordinary data edge, named port or not; a source that shares no loop with the consumer is never gated on this ground, so no loop deadlocks.
>
> 3. An edge whose source is gated by either test is unsatisfied, and a consumer therefore never runs on a mixture of rounds.

## Related rules

- Names: BR-1, BR-7, DATA-4, SG-19, SG-20
- Referenced by: BR-7

---

Rule identifiers are permanent and are never renumbered. This specification carries
no implementation status: each implementation publishes its own standing against
these rules. Licensed CC BY 4.0.