Task start and completion Changes

Changes attach predetermined effects to task activation or successful completion.

Start Changes

onStart effects run only after the task passes its start checks. Those checks include dependencies, guards, performer selection, and reservations.

WorkSpec.task("wash_vessel").onStart(() => {
  set("vessel", "state", "washing", { temporary: true });
});

If a start Change fails, the task becomes failed. The task does not become active.

Completion Changes

onComplete effects run at the task's resolved end. The runtime restores temporary values before it applies completion effects.

WorkSpec.task("wash_vessel").onComplete(() => {
  set("vessel", "state", "clean");
});

If a completion Change fails, the task becomes failed. The runtime does not report an unqualified successful completion.

Temporary effects

Pass { temporary: true } to set, change, or move in a start handler. The runtime captures the previous value and restores it when the task ends or becomes interrupted.

Temporary create and remove operations are not supported. Temporary completion operations are also invalid.

Overlapping temporary writes to the same property fail with interaction.temporary.overlap.

Same-time order

At one logical time, the runtime follows this relevant order:

1. Restore temporary values for finishing tasks.
2. Apply completion Changes.
3. Run Generator callbacks.
4. Evaluate task-start conditions.
5. Apply accepted start Changes.

Generator writes win same-target conflicts at that time. The runtime emits generator.changes.conflict as a warning.

For the full order, see the runtime execution model.