[mattt]

This PR fixes two problems in the provider tool loops on dynamic profile sessions. When a streaming response handed off from an HTTP model to a local structured model, the handoff rebuilt the prepaid snapshot with the earlier usage added and without its prepaid token, so the session counted the local requests twice. The rebuilt snapshot now keeps the token and carries the handed-off usage separately, and the session counts only the part of that usage that it hasn't counted yet.

When a tool callback changed a profile's schema prompt setting and kept the model, the next request in that response still used the old setting, because each provider computed the schema text once before its request loop. All five providers now compute the schema text after each context resolution, through one shared helper. Ordinary sessions keep the setting from the call site.