Method RunSkillFork

pkg/app/app.go:347–385

RunSkillFork dispatches a fork-mode skill in an isolated sub-session of the current parent. The parent gains a SubSession item once the runtime opens the child; the sub-session's first user message is the expanded SKILL.md body. Companion of SkillCommandFork.

(ctx context.Context, cancel context.CancelFunc, skillName, task string, _ []messages.Attachment)

// opens the child; the sub-session's first user message is the expanded
// SKILL.md body. Companion of SkillCommandFork.
func (a *App) RunSkillFork(ctx context.Context, cancel context.CancelFunc, skillName, task string, _ []messages.Attachment) {
	a.cancel = cancel

	// Mirrors App.Run's drain loop: forward events to the App bus and
	// always let StreamStoppedEvent through, even after ctx cancellation,
	// so the supervisor marks the session idle.
	go func() {
		events := make(chan runtime.Event, defaultRuntimeEventBuffer)
		go func() {
			defer close(events)
			result, err := a.runtime.RunSkillFork(ctx, a.session, skillstool.RunSkillArgs{
				Name: skillName,
				Task: task,
			}, runtime.NewChannelSink(events))
			switch {
			case errors.Is(err, runtime.ErrUnsupported):
				slog.WarnContext(ctx, "Runtime does not support fork-mode skills; skill not executed", "skill", skillName)
				a.sendEvent(ctx, runtime.Error(fmt.Sprintf("Skill %q cannot run: this runtime does not support fork-mode skills.", skillName)))
			case err != nil:
				slog.ErrorContext(ctx, "Failed to run fork-mode skill", "skill", skillName, "error", err)
				a.sendEvent(ctx, runtime.Error(fmt.Sprintf("Skill %q failed: %v", skillName, err)))
			case result != nil && result.IsError:
				a.sendEvent(ctx, runtime.Error(result.Output))
			}
		}()

		for event := range events {
			if ctx.Err() != nil {
				if _, ok := event.(*runtime.StreamStoppedEvent); ok {
					// ctx is cancelled; detach cancellation but keep its trace
					// context so the stop event still reaches subscribers.
					a.sendEvent(context.WithoutCancel(ctx), event)
				}
				continue
			}
			a.sendEvent(ctx, event)
		}
	}()
}

// defaultRuntimeEventBuffer matches Summarize and Runtime.RunStream;
// wide enough that a fork-skill sub-session won't block the producer.