Validate a model's JSON review summary

Implement validateReviewSummary(raw) (Python validate_review_summary(raw)) for the review summary contract, and predict its result for replies R1 to R8 before you run it. List the tests you would write first and the unclear cases you would confirm before coding. Then say what the dashboard should do with a rejected reply, and name two ways an accepted summary can still be wrong.

Suppose an online bookshop that sells new and secondhand books asks a language model to summarize each written customer review as JSON. A moderation dashboard shows the summary next to the review, lets moderators filter reviews by sentiment and topic, and averages the rating per book. A program reads every reply, so a reply that breaks the contract must never reach the database or the dashboard.

The replies are untrusted text: most follow the contract and some do not. The three fields mean:

• rating: the model's estimate, from 1 to 5, of how satisfied the reviewer is
• sentiment: the overall tone of the review
• topics: up to three things the review discusses, from price, delivery, condition (the physical copy), and story (the book's content)

For example, the review "Arrived two weeks late and the spine was cracked." gets this reply, and the contract accepts it:

{"rating": 2, "sentiment": "negative", "topics": ["delivery", "condition"]}

A reply is accepted only when it is a JSON object with exactly these three keys:

The validator runs these checks in this order:

• Steps 1 and 2 end validation at once: the result holds only that code.
• Steps 3, 4, and 5 each add at most one code: the first rule in the listed order that fails for that field. All three fields are always checked.
• Field codes come first in contract order (rating, sentiment, topics), then the extra codes, sorted by plain string comparison (JavaScript's default sort(), Python's sorted()). Only the extra codes are sorted.
• No code means the reply is accepted.

The result, in TypeScript terms:

type ReviewSummary = {
  rating: number; // an integer from 1 to 5
  sentiment: "positive" | "mixed" | "negative";
  topics: ("price" | "delivery" | "condition" | "story")[];
};

type ValidationResult =
  | { ok: true; value: ReviewSummary }
  | { ok: false; errors: string[] };

declare function validateReviewSummary(raw: string): ValidationResult;

Python's validate_review_summary(raw) returns a dict with the same keys, using lists, never tuples. An accepted value is a new object with its keys in contract order, rating as an integer (a Python int, also for an input such as 4.0), and topics in the reply's order. A failed result has no value key, and an accepted one has no errors key.