ajv 8.17.1: Coerce scalar values to arrays using ajv coerceTypes option

# Notes

## Search Known Solution
`search_known_solution` returned `sha256:de249b2f65992de63dd2adece0fd7b0829b25af3cd75a5ad075a49696ed69ffc` covering strict mode failure on unknown keywords (`strict: true`).

## What a Model Would Write Instead
A model writing request/query validation middleware would instantiate `new Ajv({ coerceTypes: true })` expecting query strings like `tags=tech` to automatically coerce into array fields `tags: ["tech"]`.

## Failure Mode
In Ajv 8, `coerceTypes: true` compiles cleanly with zero warnings but only coerces scalar-to-scalar types, silently failing array schema validation with `'must be array'` unless `coerceTypes: "array"` is explicitly configured.

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import Ajv from 'ajv';

export function createScalarOnlyCoercer() {
  return new Ajv({ coerceTypes: true });
}

export function createArrayCoercer() {
  return new Ajv({ coerceTypes: 'array' });
}

import { strict as assert } from 'node:assert';
import { createScalarOnlyCoercer, createArrayCoercer } from '../src/index.mjs';

const arraySchema = {
  type: 'object',
  properties: {
    tags: {
      type: 'array',
      items: { type: 'string' }
    },
    ids: {
      type: 'array',
      items: { type: 'integer' }
    }
  },
  required: ['tags', 'ids']
};

const scalarSchema = {
  type: 'object',
  properties: {
    limit: {
      type: 'integer'
    }
  },
  required: ['limit']
};

// 1. Prove that `coerceTypes: true` ONLY coerces scalar-to-scalar (limit: "10" -> 10)
const scalarAjv = createScalarOnlyCoercer();
const validateScalarLimit = scalarAjv.compile(scalarSchema);
const limitPayload = { limit: '10' };
assert.equal(validateScalarLimit(limitPayload), true);
assert.equal(limitPayload.limit, 10);

// 2. Prove that `coerceTypes: true` SILENTLY refuses to coerce scalars to arrays
const validateArrayWithScalar = scalarAjv.compile(arraySchema);
const scalarArrayPayload = {
  tags: 'tech',
  ids: '42'
};
const scalarResult = validateArrayWithScalar(scalarArrayPayload);
assert.equal(scalarResult, false, 'coerceTypes: true must NOT coerce scalar to array in ajv 8');
assert.equal(validateArrayWithScalar.errors[0].keyword, 'type');
assert.equal(validateArrayWithScalar.errors[0].params.type, 'array');
assert.equal(typeof scalarArrayPayload.tags, 'string');
assert.equal(typeof scalarArrayPayload.ids, 'string');

// 3. Prove that `coerceTypes: "array"` coerces scalar string to array of strings
//    AND coerces scalar string integer to array of integers
const arrayAjv = createArrayCoercer();
const validateArrayWithArrayCoercer = arrayAjv.compile(arraySchema);
const arrayPayload = {
  tags: 'tech',
  ids: '42'
};
const arrayResult = validateArrayWithArrayCoercer(arrayPayload);
assert.equal(arrayResult, true, 'coerceTypes: "array" must coerce scalars to arrays and nested types');
assert.deepEqual(arrayPayload.tags, ['tech']);
assert.deepEqual(arrayPayload.ids, [42]);

// 4. Prove that single-element arrays coerce to scalars with `coerceTypes: "array"`
const singleElemSchema = {
  type: 'object',
  properties: {
    query: { type: 'string' }
  },
  required: ['query']
};
const validateQuery = arrayAjv.compile(singleElemSchema);
const queryPayload = { query: ['ajv-traps'] };
assert.equal(validateQuery(queryPayload), true);
assert.equal(queryPayload.query, 'ajv-traps');

// 5. Prove that multi-element arrays are NOT coerced to scalar (preventing silent data loss)
const multiElemPayload = { query: ['first', 'second'] };
assert.equal(validateQuery(multiElemPayload), false);
assert.equal(validateQuery.errors[0].keyword, 'type');

console.log('CONTRACT PASS: ajv 8 coerceTypes="array" vs coerceTypes=true boundary proven');