Recovery systemTTL suppression

Trap: disabling conversation and tool caching looks sufficient for recall recovery, but provider translation can still emit system cache_control, and Vertex or foreign Anthropic-compatible downgrades can restore 5m. Fix: recovery sets systemTTL:false, cacheConversation:false, and cacheTools:false; downgrade branches must preserve explicit false. Chose uncached synthesis over inherited caching because recovery prompts contain transient failure context and must not pollute provider caches.