Add buildWorkflowObservationFromTask (legacy authoritative side, from a task's
terminal column/status/review/mergeDetails + recorded column history) and
buildWorkflowObservation (interpreter/shadow side, from explicit parts), plus
deriveStageTransitions (maps the task-move column history to execute/review/
merge stages) and DEFAULT_WORKFLOW_INVARIANTS. These let both sides of the
dual-observe seam produce a comparable WorkflowRunObservation without
hand-rolling the shape. Covered by workflow-parity.test.ts.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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