Return a copy with each message's content projected for the negotiated
protocol version (see PromptMessage.forVersion / Content.forVersion),
so newer content kinds and post-2024-11-05 content _meta /
Annotations.lastModified do not leak to an older peer. Mirrors
CallToolResult.forVersion.
Return a copy with each message's content projected for the negotiated protocol version (see PromptMessage.forVersion / Content.forVersion), so newer content kinds and post-2024-11-05 content _meta / Annotations.lastModified do not leak to an older peer. Mirrors CallToolResult.forVersion.