CONTEXT CONSTRUCTION (THE CONTEXT BUILDER)

CHAPTER SUMMARY The context builder assembles the exact text the model sees before every call. Prompt composition builds the system prompt from modular, labeled blocks so that it is easy to read, test, reuse, and keep fresh. System reminders are short, specific notes re-injected near the end of the context to keep behavior on track, but they supplement and do not replace enforcement in code. Selection chooses recent messages, anchors, relevant files, and trimmed tool outputs, and leaves out the rest. Ordering places critical rules at the start and again near the end, with bulky material in the middle, and labeled formatting separates instructions from data. KEY TERMS REVIEW Context builder: the harness component that assembles the model's input on each call. System prompt: the standing instructions at the start of the context. Prompt composition: building the system prompt from modular pieces. System reminder: a short re-injected note that keeps behavior on track. Sliding window: keeping only the most recent messages in full. Anchor: an item that is never dropped, such as the original task. Side effect: a change a function makes outside of returning its result.