Spring AI: Message Parts Doc | Upgrade Notes | OpenAI Responses Doc | Session Doc Reasoning models do more than think before they answer. They hand part of that thinking back to you and expect to get it back on the next request. Claude signs its thinking blocks. Gemini attaches thought signatures to its function calls. OpenAI's Responses API returns encrypted reasoning items. If you drop, reorder or edit them, the result ranges from an HTTP 400 to a model that quietly loses its earlier reasoning and starts over. Until now, a Spring AI message was a piece of text with side lists of tool calls…