When the work stage completes with a derived task list, create Fusion tasks via
ctx.taskStore.createTask tagged CE-originated (sourceType workflow_step +
sourceMetadata marker) and record an authoritative ce_pipeline_links row per
task (back-reference lives in the link table, not task-row JSON, per FN-5719).
Tasks then run the normal lifecycle untouched. Zero derived tasks is a clean
no-op. The link store is intentionally minimal for U8 to extend with the
bidirectional pipeline-state machine.
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