Project the final GetPromptResult to the negotiated protocol version so
version-gated message content (audio/resource_link/tool_use/tool_result
plus content-level _meta/lastModified) is not emitted to peers that do
not understand it. Mirrors ToolResponse.forVersion: an
InputRequiredResult is draft-only (MRTR) and carries no version-gated
content, so it is returned unchanged.
Project the final GetPromptResult to the negotiated protocol version so version-gated message content (audio/resource_link/tool_use/tool_result plus content-level _meta/lastModified) is not emitted to peers that do not understand it. Mirrors ToolResponse.forVersion: an InputRequiredResult is draft-only (MRTR) and carries no version-gated content, so it is returned unchanged.