GenServer managing a single workflow's execution lifecycle.

The Worker implements the dispatch loop: plan → prepare → dispatch → apply, using an Executor behaviour for fault-isolated task execution and PolicyDriver for policy-aware invocation.

Workers are started under the Runner's DynamicSupervisor and registered in the Runner's Registry for lookup by workflow ID.

Executor

The executor controls how runnables are dispatched to compute. By default, Runic.Runner.Executor.Task is used (wrapping Task.Supervisor.async_nolink). Pass executor: MyExecutor and executor_opts: [...] to use a custom executor.

The special value executor: :inline executes runnables synchronously in the Worker process — useful for sub-millisecond computations where task spawn overhead dominates.

Per-Component Executor Overrides

When a SchedulerPolicy for a runnable includes an :executor field, the Worker dispatches that runnable through the override executor instead of the default. This allows mixing execution strategies within a single workflow.

Scheduler

The scheduler controls what gets dispatched together and when. Pass scheduler: MyScheduler and scheduler_opts: [...] to use a custom strategy. Built-in schedulers:

• Runic.Runner.Scheduler.Default — dispatches each runnable individually (default)
• Runic.Runner.Scheduler.ChainBatching — batches linear chains into Promises

The promise_opts: [min_chain_length: N] shorthand is equivalent to scheduler: Runic.Runner.Scheduler.ChainBatching, scheduler_opts: [min_chain_length: N]. An explicit :scheduler takes precedence over :promise_opts.

Hooks

Lifecycle hooks allow observability and light customization without replacing the Worker. Pass hooks: [...] in Worker opts:

• on_dispatch: fn runnable, worker_state -> :ok end
• on_complete: fn runnable, duration_ms, worker_state -> :ok end
• on_failed: fn runnable, reason, worker_state -> :ok end
• on_idle: fn worker_state -> :ok end
• transform_runnables: fn runnables, workflow -> runnables end

Hook exceptions are logged but do not crash the Worker.