The blocks of content that compose the user's message.

As a baseline, the Agent MUST support [ContentBlock::Text] and [ContentBlock::ResourceLink], while other variants are optionally enabled via [PromptCapabilities].

The Client MUST adapt its interface according to [PromptCapabilities].

The client MAY include referenced pieces of context as either [ContentBlock::Resource] or [ContentBlock::ResourceLink].

When available, [ContentBlock::Resource] is preferred as it avoids extra round-trips and allows the message to include pieces of context from sources the agent may not have access to.

A unique identifier for a conversation session between a client and agent.

Sessions maintain their own context, conversation history, and state, allowing multiple independent interactions with the same agent.

Example

use agent_client_protocol::SessionId;
use std::sync::Arc;

let session_id = SessionId(Arc::from("sess_abc123def456"));
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See protocol docs: Session ID