agenthub · transform.compose_message
Compose Message
Assemble the canonical messages array — system, then history, then the current user turn — from three independent sources.
Why the node earns its place
It exists so Prompt Template, Memory Fetch and Chat Input can each stay focused on one job. The system prompt comes from one, the prior turns from another, the current text from a third, and this node is the only place that knows what order a model expects them in.
How it works at run time
- 1Take
systemas the system message when present. - 2Append
history— prior turns, as Memory Fetch emits them. - 3Append the current
usertext last.
What you wire
Inputs
- systemstring
- historyarray
- userstring
Outputs
- messagesarray
Configuration
Nothing to configure — this node has no settings of its own.
What usually goes wrong
Watch for this
If the model complains about an empty messages array, the missing piece is usually user — Chat Input resolved nothing and emitted an empty string. Check there before rewiring this node.
Behaviour & provenance