-- 030_plan_step_replaced_reason.up.sql
-- Add replaced_reason to session_plan_steps so the agent must explain why
-- a step was replaced (wrong_diagnosis, scope_change, blocked, superseded,
-- operator_override) rather than silently replacing entire plans. The column
-- is also set by bulk-replace operations (proposePlan, setGoal, reopenSession)
-- for auditability.

ALTER TABLE session_plan_steps ADD COLUMN IF NOT EXISTS replaced_reason TEXT;