A useful answer depends on the evidence supplied to the model. Retrieval chooses material, context engineering assembles the current working set, and memory keeps selected information available for future tasks.
Begin with the retrieval pipeline and the distinction between embeddings, rerankers and classifiers. Then study context budgets and memory updates. QMD, zvec-grep and Basic Memory are implementations of different parts of this work, not mandatory stages in one stack.
For a missed answer, locate the failure: absent source, missed candidate, poor ranking, lost context or unsupported generation. Preserve source references and use retrieval/generation evaluation to test each boundary.