Cost Completeness — No More Silent $0 Windows

Goal

Epic A2 / #752: terminal jobs must leave a cost_entries row, and ops must flag when they do not.

Shipped

1. Ops — jobs_missing_cost, cost_missing_rate, samples; finding when gap is large or entries=0 with many terminal jobs.
2. Reconcile — _ensure_daemon_job_cost_entry so preferred-summary short-circuit still writes costs; retry if update_costs throws.
3. Epic plan marks A2.1/A2.2 shipped.

Next

A3 home/headless dispatch_context (#740). Pricing accuracy (#787) remains Epic C.