The model supplies capability. The harness turns capability into conduct.
From the Daily trail
Before the Prompt Lands: Codex and Gemini Turn Hooks Into Agent Control Planes: Shows that agent work can be inspected, enriched, blocked, or reshaped before the model sees the task.
Codex forks it, Gemini threads it: execution context becomes first-class: Connects birth to thread identity, execution context, and forked work.
The prompt is not the first moment
The public myth says the agent begins at the prompt. The source trail says something more interesting: serious agent systems do work before the model says anything. They resolve a session, choose a role, attach policy, prepare the workspace, expose tools, and decide what kind of state will survive the turn.
That is why two products using similarly strong models can feel radically different. One feels like a cautious local worker, another like a team manager, another like a terminal-native collaborator. The difference is not only model quality. It is birth architecture.
Birth means bounded identity
The Daily Edition makes this concrete through hooks, thread identity, goals, context state, permission profiles, tool modes, and subagent lineage. Codex reporting repeatedly shows spawned work inheriting or carrying role, thread, permission, and parentage state. Gemini CLI's public docs and repo frame a terminal agent with built-in tools, MCP support, and subagent machinery.
The chapter's useful line is simple: identity is not only personality. It is also the set of boundaries that tells a model where it is, what job it has, what it may touch, and how its actions will be seen.
Why this changes the reader's mental model
A chatbot can answer. An agent is prepared to act. That preparation is the first architectural commitment. Before output, the system has already answered questions the user may never see: is this local or remote, ephemeral or durable, solo or delegated, sandboxed or trusted, interactive or backgrounded?
Once readers see birth as architecture, every later chapter becomes easier. Context is not just prompt text. Tools are not just buttons. Memory is not just a transcript. Safety is not an interruption. The agent is a designed actor from its first breath.