/api/v1/environments/{id}/conversations/{conversationId}/messages

Messages oldest→newest, whitelisted projection (`id, role, content, createdAt, kind,

model, spans) plus truncated when the page cap cut older history. spans` carries

the server-side first-token marks (t6-t9 epoch ms + firstTokenMs) of agent replies —

only the FIRST turn writes environment milestones, every reply carries its own

metadata.eaas.spans. t9 is the server-side reply-persisted projection; the

client-side render moment is not observable by the cloud.