code-review-context

Codex maintains a context (history of messages) that is sent to the model in inference requests.

1. No history rewrite - the context must be built up incrementally.
2. Avoid frequent changes to context that cause cache misses.
3. No unbounded items - everything injected in the model context must have a bounded size and a hard cap.
4. No items larger than 10K tokens.
5. Highlight new individual items that can cross >1k tokens as P0. These need an additional manual review.
6. All injected fragments must be defined as structs in core/context and implement ContextualUserFragment trait