test: implement type-checked test fixtures

[kantord]

a little refactor I did yesterday for the auto mocking system. What it includes:

• type checking even for auto-generated fixtures. This means that you get appropriate type failures for the mocks when BE introduces changes to the schema and you don't need to rely on test failures to know that you need to update a fixture.
• improve the folder structure for fixtures

Old folder structure

New folder structure

Type checkable automatic mocks

Example:

import type { GetApiV1BetaGroupsResponse } from '@api/types.gen'

export default {
  groups: [
    { name: 'default', registered_clients: ['client-a'] },
    { name: 'Research team', registered_clients: ['client-b'] },
    { name: 'Archive', registered_clients: [] },
  ],
} satisfies GetApiV1BetaGroupsResponse

[Copilot]

Pull Request Overview

Refactors the mocking system to implement type-checked test fixtures by converting JSON fixtures to TypeScript modules with type imports and satisfies clauses. This ensures compile-time validation of mock data against OpenAPI-generated types.

• Converted auto-generated fixtures from JSON to TypeScript format with type checking
• Improved fixture folder structure with shorter path names and nested directories
• Updated mock generation logic to create type-safe fixtures with proper imports

Reviewed Changes

Copilot reviewed 19 out of 19 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
use-mutation-restart-server.test.ts	Enhanced test with proper async handling and query client state validation
mocker.ts	Core refactor to generate TypeScript fixtures with type checking and improved file organization
mockTemplate.ts	New utility to generate TypeScript module templates with conditional type imports
Various fixture files	Converted from JSON to TypeScript format with type imports and satisfies clauses
customHandlers/index.ts	Removed redundant handlers now covered by auto-generated fixtures
fixtures/README.md	Updated documentation to reflect TypeScript fixture format