Workflow Engine

The Workflow Engine executes the step graph produced by the Orchestrator. It resolves dependencies, runs independent steps in parallel, threads data between steps through a shared context, and supports pausing for human review.

What a step carries

Field	Meaning
`id`	Unique step identifier
`agent`	The capability group that owns the tool
`action`	The tool to invoke
`args`	Inputs; may contain `$key` variables
`depends_on`	Steps that must complete first
`outputs`	Values this step produces
`retry`	How many times to retry on failure
`timeout`	Maximum time the step may run
`needs_human`	If true, pause for review before executing
`persona`	Optional specialized role

Execution model

Scheduling

Steps whose dependencies are all satisfied become ready and are dispatched together.

Parallel dispatch

Ready steps run concurrently, up to a sensible bound (a handful at a time).

Variable substitution

Before a step runs, $key references in its inputs are replaced with values produced by earlier steps.

Execute & record

The tool runs; its result, outputs, and status are recorded.

Shared context & variable passing

Steps communicate through a shared key/value context. A step declares what it produces in outputs, and downstream steps consume those values with $key in their inputs:

[
 { "id": "s1", "agent": "web_search", "action": "SEARCH_WEB",
 "args": { "query": "AI news" }, "outputs": ["results"] },

 { "id": "s2", "agent": "email", "action": "SEND_EMAIL",
 "args": { "to": "$user_email", "body": "$results" },
 "depends_on": ["s1"] }
]

Common ambient variables like $user_name and $user_email are resolved from the shared context too.

Human-in-the-loop

A step marked needs_human pauses before executing, surfacing the workflow for review. Workflows can be interrupted and resumed via the Workflows API:

Endpoint	Action
`POST /api/workflows/{id}/interrupt`	Pause a running workflow
`POST /api/workflows/{id}/resume`	Resume a paused workflow
`POST /api/workflows/{id}/intervene`	Inject human input / edits

Resilience

Retries — each step retries on failure up to its configured limit.
Timeouts — each step is bounded by a maximum run time.
Runtime capability creation — if a step's tool is still missing at execution time, the engine can create it as a safety net.

History

Completed workflows are saved locally and exposed via GET /api/workflows and GET /api/workflows/{id}. Recurring/scheduled workflows are managed automatically — see the Workflows API and Automation.