The result of flattening a Theia message history into a single prompt for the agentic Copilot SDK session.
Optional
Base64-encoded images pulled out of the user's messages, sent alongside the prompt.
The user-facing prompt body derived from the non-system messages.
Concatenated content of all system messages (may be empty).
The result of flattening a Theia message history into a single prompt for the agentic Copilot SDK session.