---
id: MEM-4
family: GR-MEM
level: extended
profiles: [storage-api, runtime]
posture: normative-target
added: "1.0"
changed: "1.0"
source: https://flowdrop.io/spec/rules/gr-mem/mem-4
specification: FlowDrop Workflow Specification 1.0-draft
licence: CC BY 4.0
---

# MEM-4 — Assembling messages concatenates in declared port order

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

The node that joins several message sources into one list. Port order is the message order, and an unwired source adds nothing at all.

## The rule

> **Normative.** This is the rule.
>
> 1. A message-assembly node takes any number of dynamically declared message-typed inputs and flattens them into one message-typed output.
>
> 2. The declared order of the inputs is the order of the messages.
>
> 3. A connected list contributes each of its items in order; a connected single message contributes one item; an input that is unwired or carries no value contributes nothing; no placeholder is emitted for it.


## What it means

The output order follows how the author declared the ports, not the order a
caller might expect from the port names or from wiring them up. Declare `b`
before `a` and wire both — `b`'s messages come first regardless of what the
names suggest.

The other clause is the one a reader coming from a message-merging node would
get wrong: an input port that is unwired, or carries no value, contributes
nothing at all — no null placeholder takes its place in the output. A
three-port assembly with the middle port unwired produces a two-item list,
not a three-item list with a gap in it.

## Example

Two ports declared in the order `b`, then `a`, each wired to one message:

```json title="Ports declared b before a" verdict="assembled"
{ "b": [{ "role": "user", "content": "second-declared-first" }], "a": [{ "role": "user", "content": "first-declared-second" }] }
```

```json title="What the assembly outputs"
[{ "role": "user", "content": "second-declared-first" }, { "role": "user", "content": "first-declared-second" }]
```

Three ports declared, the middle one left unwired:

```json title="in_1 and in_3 wired, in_2 left unwired" verdict="assembled"
{ "in_1": [{ "role": "user", "content": "a" }], "in_3": [{ "role": "user", "content": "c" }] }
```

```json title="What the assembly outputs"
[{ "role": "user", "content": "a" }, { "role": "user", "content": "c" }]
```

## Related rules

- Names: MEM-16
- Referenced by: MEM-16

---

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.