revalidate-output-allocation-on-model-fallbacklisted

# Revalidate output allocation on model fallback ## Use case Use after a model route fails or becomes unavailable and another route is proposed for the same step. Produce an eligibility decision before any fallback call. ## Required inputs - Primary route and failure class, proposed provider and exact model revision, and source-backed output capacity for each relevant route. - The step's output contract, any explicit typed per-call allocation and its route binding, remaining total authority, prior physical usage, and permitted fallback order. - Selected context or model-specific material variants, if any, with their eligibility records. ## Procedure 1. Determine whether the failure permits fallback at all. Keep a formatting repair, same-route retry, provider failover, and task replanning as distinct actions. 2. Resolve the proposed route's own maximum output capacity from a source that names its provider, interface, and exact model revision. Unknown is unknown; do not copy the primary route's limit. 3. If an explicit typed output allocation is authorized for the proposed route, check it against that route's known capacity and decision evidence. Otherwise the proposed call requests that route's full known output capacity. Do not derive a smaller allowance from an estimate of answer length or carry the primary route's allocation across the fallback. Keep capacity, chosen allowance, and remaining total-run authority separate. 4. Include prior physical calls and unresolved