Fix two samples broken by the previous round, and a contradictory claim

[GuanzhouSong]

A second review pass — same rubric, same three models — was run after the previous fixes merged. It executed the samples against a live gateway instead of reading them, and two of the three broken commands it found had been introduced by that previous round. That is the re-review doing its job.

1. The replacement Node.js example did not run

Reproduced independently by two models:

FAIL "Creating collections" block as pasted:  ReferenceError: db is not defined
FAIL "Document operations" block as pasted:   ReferenceError: db is not defined

const db was declared inside a connect() that is never called, so the following blocks referenced it out of scope. They also used top-level await outside an async function — a second paste failure.

Replaced with one self-contained main() that connects, operates and closes, plus a sentence explaining why these statements cannot be pasted at the top level.

2. The $vectorSearch fix was incomplete

Moving it from find() to aggregate() was correct but not sufficient — the stage needs a vector index and the page never created one:

FAIL $vectorSearch (as documented): OperationFailure: Similarity index was not found
     for a vector similarity search query.  {'ok': 0.0, 'code': 2, 'codeName': 'BadValue'}

The reviewer confirmed the stage works once an index exists. Added the createIndexes call — matching the form the mongo-shell quick start already uses — and the dimensions caveat.

3. postgres-api/index.md contradicted itself

Line 8 said DocumentDB "consists of three PostgreSQL extensions". Line 56 of the same page correctly describes pg_documentdb_gw as a standalone process that can optionally run as a background worker via a separate pg_documentdb_gw_host extension. It is two extensions and a gateway.

Verification

The two sample failures were reproduced by both Opus 5 and GPT-5.6 Sol independently, each executing the code against a live documentdb-local container rather than reading it.

Related

documentdb/documentdb.github.io#162 — the website-owned copy of the Node.js prerequisite floor.