Listener and Client Nodes

Every routing policy contains two fixed nodes that anchor the graph's entry and exit. They are structural rather than functional: neither transforms the Context, but both are required by validation — a policy without a listener node or without a client node is rejected before it can be compiled.

nodes:
  - id: listener
    type: listener
  # ... plugin nodes ...
  - id: client
    type: client

Listener node — the entry point

The listener represents the matched request from the ingress listener. When a route matches, the gateway builds the initial Context — request populated from the incoming request, response empty, message and errors empty — and execution begins at the node the listener's edge points to.

• The listener's output port is out (compiled identically to success).
• The entry node of the compiled graph is the target of the listener's out/success edge — the first node that actually executes per request:

edges:
  - from: listener.out
    to: rewrite-request.in   # rewrite-request is the entry node

• Compilation fails outright if the policy has no listener node.

Client node — the terminal exit

The client node represents the requesting client. It is recorded as a terminal at compile time: when the Context reaches a client node, graph execution stops and the gateway sends context.response back to the caller (a status_code of 0 becomes 200).

• The client node is a passthrough — it does not modify the Context.
• Unlike regular inputs, a client node's in port may have multiple incoming edges. Validation enforces at most one edge per input port for ordinary nodes, but explicitly exempts client (and error-handler) nodes — so the happy path and any error-handler paths can all deliver the final response through the same client node:

edges:
  - from: rewrite-response.success
    to: client.in            # happy path
  - from: error-handler.success
    to: client.in            # error path, same client node

In the web UI

On the canvas the listener is pre-placed on the left as the starting point and the client on the right as the endpoint. Both are fixed and non-removable; plugin nodes are wired between them.

Summary

	Listener	Client
Role	Graph entry point	Graph exit point (terminal)
Behavior	Emits the initial Context	Passthrough; execution stops here, context.response is sent
Ports	out output	in input
Incoming edges	—	Multiple allowed
Required	Yes (validation and compilation)	Yes (validation)