fix: replay reasoning as encrypted content

[Im-Beast]

• Replays reasoning between tool calls as encrypted_content instead of a bare rs_ id, so the endpoint never looks the item up in its response store
• Function calls always get synthetic ids for the same reason
• Fixes the Item with id 'rs_...' not found 400s on Azure, where the store may not hold the response yet when the next request arrives
• Reasoning returned without a blob is not replayed
• Bumps to 0.6.16