---
id: SCH-40
family: GR-SCHEMA
level: extended
profiles: [storage-api, runtime, editor-client]
posture: normative-target
added: "1.0"
changed: "1.0"
source: https://flowdrop.io/spec/rules/gr-schema/sch-40
specification: FlowDrop Workflow Specification 1.0-draft
licence: CC BY 4.0
---

# SCH-40 — A port's lane is consumed at a public boundary

*GR-SCHEMA (Part I) · level: extended · profiles: storage-api, runtime, editor-client · added in 1.0*

The lane a port declares is not only a colour on a canvas. It is the shared answer to "what may a caller supply?" at the endpoints that start a workflow and take a turn in a session.

## The rule

> **Normative.** This is the rule.
>
> 1. A port's declared lane decides what a caller may supply at a workflow's public entry points: launching a workflow and taking a turn in a session answer from the same check.
>
> 2. A port on the sink or on a control lane places no constraint: any JSON value is accepted, including an array or null.
>
> 3. Narrowing that, for instance by keying the check off JSON Schema's seven type words alone, is strictly stronger and is a breaking change to a public endpoint: it is announced, never carried in on a refactor.
>
> 4. The name a projection gives the field that carries the lane is likewise a client-facing contract.

## Related rules

- Names: SCH-35, SCH-37
- Referenced by: SCH-35

---

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.