---
id: reactive/node-status
name: Implement node status signal management and computed preconditions + blockedByFailure
status: completed
depends_on:
  - reactive/workflow-root
  - schema/enums
scope: moderate
risk: high
impact: component
level: implementation
---

## Description

Implement the reactive node status management layer: `signal<NodeStatus>` per-node lifecycle tracking, `computed<boolean>` precondition resolution, `computed<boolean>` blockedByFailure detection, and the effects that wire them together to drive automatic state transitions.

## Acceptance Criteria

- [ ] `src/reactive/node-status.ts` exports precondition computation, blockedByFailure computation, and status transition effects
- [ ] `computePreconditions(node, ctx): boolean` — Sequential: previous sibling completed/skipped; Parallel: parent preconditions met; Conditional: condition evaluates; root nodes: true (no predecessors)
- [ ] `computeBlockedByFailure(node, ctx): boolean` — any predecessor is failed/aborted
- [ ] Start effect: `if (preconditions.value && (status === "idle" || "waiting")) → transition to "ready"`
- [ ] Abort effect: `if (blockedByFailure.value && (status === "idle" || "waiting")) → transition to "aborted"`
- [ ] `skipped` satisfies preconditions — a skipped predecessor is treated as "completed for precondition purposes"
- [ ] `failed` and `aborted` block preconditions — dependents can never become ready
- [ ] Failure follows dependency edges, not structural scope — sibling branches in Parallel are independent
- [ ] Effects are tracked by `WorkflowReactiveRoot.effectDisposers` and cleaned up by `dispose()`
- [ ] Unit tests: sequential preconditions, parallel preconditions, join (fork-join) preconditions, blockedByFailure cascade, skipped satisfies preconditions, failure isolation in parallel branches

## References

- docs/architecture/reactive-execution.md — computed preconditions, blockedByFailure, status propagation effects, failure isolation
- docs/architecture/host-configs.md — WorkflowNode, prerequisite computation

## Notes

> To be filled by implementation agent

## Summary

> To be filled on completion