68e889b14c39 for production systems — contracts and checks

The following notes reconstruct a practical path around “”. Emphasis stays on contracts, checks, and drop-in code placeholders rather than motivational framing. When working through the Overview stage, write down the contract first: required inputs, success signal, and what happens on partial failure. That checklist keeps later code changes honest. Record timings and token or query cost next to functional results. Cost visibility early prevents surprise bills when the path moves from demo to shared environments.

1. Embeddings turn meaning into geometry

The 1 Embeddings turn meaning stage works best when treated as a measurable surface. Capture one golden transcript, one failure case, and the rollback note before expanding scope. Keep configuration outside application code. Environment files, secret stores, and feature flags belong in one place operators can audit without reading the whole graph. Separate chunking policy from retrieval policy. Changing one should not force a rewrite of the other when quality metrics move.

# pip install openai
# export OPENAI_API_KEY=sk-...
import math

from openai import OpenAI

client = OpenAI()


def embed(texts):
    resp = client.embeddings.create(
        model="text-embedding-3-small",
        input=texts,
    )
    return [d.embedding for d in resp.data]


def cosine(a, b):
    dot = sum(x * y for x, y in zip(a, b))
    na = math.sqrt(sum(x * x for x in a))
    nb = math.sqrt(sum(y * y for y in b))
    return dot / (na * nb)


q, hit, miss = embed([
    "How do I get my money back?",
    "Refunds are possible within 14 days "
    "of purchase.",
    "Data is stored in Frankfurt and "
    "encrypted at rest.",
])

print(f"refund doc:  {cosine(q, hit):.3f}")
print(f"storage doc: {cosine(q, miss):.3f}")

2. A vector store is a list you can rank

The 2 A vector store stage works best when treated as a measurable surface. Capture one golden transcript, one failure case, and the rollback note before expanding scope. Document the happy path and the recovery path together. Retries, human gates, and dead-letter handling are part of the product, not later polish. Pin dependency versions and record the image digest that ran the demo. Reproducibility beats tribal knowledge.

class VectorStore:
    def __init__(self):
        self.texts = []
        self.vectors = []

    def add(self, texts):
        self.texts.extend(texts)
        self.vectors.extend(embed(texts))

    def top_k(self, query, k=3):
        q = embed([query])[0]
        scored = [
            (cosine(q, v), t)
            for v, t in zip(
                self.vectors, self.texts
            )
        ]
        scored.sort(
            key=lambda s: s[0], reverse=True
        )
        return scored[:k]


store = VectorStore()
store.add([
    "Refunds are possible within 14 days.",
    "The Pro plan costs 12 EUR per month.",
    "Data is stored in Frankfurt.",
])

for score, text in store.top_k(
    "can I cancel and get a refund?", k=2
):
    print(f"{score:.3f}  {text}")

3. The full pipeline: retrieve, augment, generate

The 3 The full pipeline stage works best when treated as a measurable surface. Capture one golden transcript, one failure case, and the rollback note before expanding scope. Prefer small, testable units over sprawling scripts. When a step fails, the failure should point at a single responsibility rather than a tangled pipeline. Separate chunking policy from retrieval policy. Changing one should not force a rewrite of the other when quality metrics move. The 3 The full pipeline stage works best when treated as a measurable surface. Capture one golden transcript, one failure case, and the rollback note before expanding scope. Record timings and token or query cost next to functional results. Cost visibility early prevents surprise bills when the path moves from demo to shared environments.

# examples/part07_rag.py
# Mini RAG in ~90 lines: embed -> store -> top-k
# -> stitch into messages -> generate.
#
# Setup:
#   pip install openai
#   export OPENAI_API_KEY=sk-...
#
# Run:
#   python part07_rag.py

import math

from openai import OpenAI

client = OpenAI()

EMBED_MODEL = "text-embedding-3-small"
CHAT_MODEL = "gpt-4o-mini"

# A tiny corpus. In real life these are chunks
# of your docs, not whole documents.
DOCS = [
    "Support hours are 9am to 6pm CET, "
    "Monday to Friday.",
    "Refunds are possible within 14 days "
    "of purchase, no questions asked.",
    "The Pro plan costs 12 EUR per month "
    "and includes API access.",
    "The Free plan allows 3 projects and "
    "community support only.",
    "Data is stored in Frankfurt and "
    "encrypted at rest with AES-256.",
    "You can export all your data as "
    "JSON from the settings page.",
]


def embed(texts):
    resp = client.embeddings.create(
        model=EMBED_MODEL,
        input=texts,
    )
    return [d.embedding for d in resp.data]


def cosine(a, b):
    dot = sum(x * y for x, y in zip(a, b))
    na = math.sqrt(sum(x * x for x in a))
    nb = math.sqrt(sum(y * y for y in b))
    return dot / (na * nb)


class VectorStore:
    """A list of (vector, text) pairs. That is
    all a vector store is, before you need
    scale."""

    def __init__(self):
        self.texts = []
        self.vectors = []

    def add(self, texts):
        self.texts.extend(texts)
        self.vectors.extend(embed(texts))

    def top_k(self, query, k=3):
        q = embed([query])[0]
        scored = [
            (cosine(q, v), t)
            for v, t in zip(
                self.vectors, self.texts
            )
        ]
        scored.sort(key=lambda s: s[0], reverse=True)
        return scored[:k]



def build_messages(question, hits):
    context = "\n\n".join(
        f"[{i + 1}] {text}"
        for i, (_, text) in enumerate(hits)
    )
    system = (
        "Answer using only the context below. "
        "If the answer is not in the context, "
        "say you do not know.\n\n"
        "Context:\n" + context
    )
    return [
        {"role": "system", "content": system},
        {"role": "user", "content": question},
    ]


def ask(store, question):
    hits = store.top_k(question, k=3)
    print(f"Q: {question}")
    for score, text in hits:
        print(f"  {score:.3f}  {text[:44]}...")
    messages = build_messages(question, hits)
    resp = client.chat.completions.create(
        model=CHAT_MODEL,
        messages=messages,
    )
    return resp.choices[0].message.content


if __name__ == "__main__":
    store = VectorStore()
    store.add(DOCS)

    answer = ask(
        store,
        "Where is my data stored, and can "
        "I get it out?",
    )
    print(f"A: {answer}")

Where the toy version breaks

For the Where the toy version stage, define the inputs, the owner of the step, and the exit criteria before changing code. Operators should be able to re-run the step from a known checkpoint without guessing hidden state. Keep configuration outside application code. Environment files, secret stores, and feature flags belong in one place operators can audit without reading the whole graph. Add a smoke test that exercises the critical path in CI with fixtures, not live paid APIs, whenever budgets allow.

Operational checklist

For the Operational checklist stage, define the inputs, the owner of the step, and the exit criteria before changing code. Operators should be able to re-run the step from a known checkpoint without guessing hidden state.

Treat this stage as a contract between inputs and validated outputs. Name the artifacts, define success checks, and refuse silent partial completion.

Add a smoke test that exercises the critical path in CI with fixtures, not live paid APIs, whenever budgets allow.

Prefer small, testable units over sprawling scripts. When a step fails, the failure should point at a single responsibility rather than a tangled pipeline.

Pin dependency versions and record the image digest that ran the demo. Reproducibility beats tribal knowledge.

Document the happy path and the recovery path together. Retries, human gates, and dead-letter handling are part of the product, not later polish.

Before promoting the stack, freeze versions, capture a golden transcript for the critical path, and confirm rollback steps. Shared environments need rate limits, tenancy checks, and a clear owner for secret rotation. Prefer boring reliability over clever one-off demos.

Batch note for 68e889b14c39: keep provider keys out of the repo, set a per-session token ceiling, and store transcripts next to the eval fixtures so later model swaps stay comparable.