Agent Knows Only Files Question Explained
This worked Harness Engineering practice question tests Harness Basics. Try the answer first, then review why C is the best choice.
Short answer
The correct answer is C. No file or message in this session holds the price.
A new coding-agent session starts with a fresh context. The agent can use a fact only if your prompt or a file it reads holds that fact. A chat message from an earlier session is not part of the new one, so the agent guessed. OpenAI's Codex team puts it as "anything it can't access in-context while running effectively doesn't exist." Claude Code's auto memory saves some notes on its own, but it chooses what to save. Put the price in a project file, and add a line in AGENTS.md that names that file. The correct answer is C. No file or message in this session holds the price
The Question
Last week you told your agent in chat that tea costs $3. Today, in a new session, you ask it to add tea to the menu page. It writes $4 without hesitation. Why?
Why C is correct
A new coding-agent session starts with a fresh context. The agent can use a fact only if your prompt or a file it reads holds that fact. A chat message from an earlier session is not part of the new one, so the agent guessed. OpenAI's Codex team puts it as "anything it can't access in-context while running effectively doesn't exist." Claude Code's auto memory saves some notes on its own, but it chooses what to save. Put the price in a project file, and add a line in AGENTS.md that names that file. The correct answer is C. No file or message in this session holds the price
Why the other options are wrong
No model knows your shop's tea price. The price is a fact about your project, so it has to come from a file the agent can open.
Length is not the cause. A new session does not load last week's conversation at all, whether it was long or short.
No file in the folder holds a price, so the agent had nothing to round. It produced a confident guess.
Key idea: Harness Basics
Every question here is a situation you meet with Claude Code or Codex: the agent gets something wrong, and you choose what to change. The best answer is usually a file, a check, or a hook that stops the mistake from repeating, not a louder prompt. If you miss a question, read the explanation and note which part of the harness it uses: the AGENTS.md map, a skill, a check, a visitor check, a hook, or a handoff note.
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