feat(engine,core): U5+U6+U12core — step-review verdict handler, graph-source projection discipline, pluggable step-parser registry
- step-review node: reviewStep seam, verdict→outcome edges, UNAVAILABLE limiter, rethink reset-on-rework, split-branch advisory-only
- updateStep source:'graph': dependency-order done guard, audit-loud suppression, auto-reinit bypass; projection-first ordering
- runGraphTaskStep: per-step step-session physics pinned for graph-owned runs (closes U3 interim)
- step-parsers.ts registry (step-headings byte-identical move + json-steps), store delegates via registry
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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