# AGENTS.md

## Must-follow constraints

- Use `bun` only. Do not use `npm` or `pnpm`.
- Do not start the dev server (`bun run dev`); assume it is already running.
- If you change `prisma/schema.prisma`, run `bun run db:generate`.
- In App Router dynamic routes, keep `params` typed as `Promise<...>` and `await params` in handlers/pages.

## Validation before finishing

- Run `bun run check`.
- Run `bun run verify` (this is `bun run check` plus the unit and component tests).
- If you touched an API route, also run `bun run test:api`. It needs the test database:
  `bun run test:db:up` first.
- If you added a batch of tests, hand them to a second reviewer before calling the work
  done. See "A batch of new tests gets an adversarial review, by somebody else" below.

## Testing

- The testing stack, layout and conventions live in `TESTING.md`. Read it before adding a
  test.
- Tests live in a top-level `tests/` tree, never colocated with the code.
- Import test globals explicitly: `import { describe, it, expect, vi } from 'vitest';`.
- Never write a BigInt literal (`1n`) in any file. `tsconfig.json` targets ES2017, so `tsc`
  rejects the syntax with TS2737 and `bun run check` fails. Use `BigInt(1)` instead, and
  compare `BigInt(...)` against `BigInt(...)`.

### When a change needs a test

Match the change to a layer. Most changes need exactly one.

| You changed                                                                                                     | Write                                                                           |
| --------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------- |
| A pure function in `lib/` (validation, a limit, a date rule, a URL or filename check, a permission calculation) | a unit test in `tests/unit/lib/`                                                |
| An API route, or any authorization, quota or billing rule behind one                                            | an integration test in `tests/api/`                                             |
| A new API route                                                                                                 | classify it in `tests/api/auth-matrix.test.ts`, or the suite fails until you do |
| Real logic in a React hook (optimistic updates, throttling, retries)                                            | a hook test in `tests/component/hooks/`                                         |
| A user-visible flow across more than one page                                                                   | an end-to-end spec in `tests/e2e/`                                              |
| Presentation only (styling, copy, layout, a `components/ui/` wrapper)                                           | nothing                                                                         |

Always write a test for a bug fix, at the layer where the bug lived. The test must fail
before the fix and pass after it. If it passes before the fix, it is testing the wrong
thing.

For an API route, three cases are the minimum: an unauthenticated caller, a caller who is
signed in but not authorized, and the happy path. Assert the database row, not only the
status code: a refused DELETE has to leave the row present.

### Two ways a test can be worthless

Both have been found in this repo, so they are worth naming.

1. **A test that cannot fail.** Before you finish, name the specific mutation of the
   production code your test would catch. If you cannot name one, delete the test. When it
   matters, prove it: break the code on purpose, watch the test go red, then revert.
2. **A test whose input comes from the code under test.** Iterating the same constant the
   function looks up means deleting an entry from that constant also deletes its own test
   case. Write expected values by hand as literals.

A third variant is specific to `tests/api/auth-matrix.test.ts`: a route that refuses a
malformed request before it reaches its access check produces an entry that passes whether
or not the guard exists. The suite catches it by requiring a 401 or a 403 rather than
merely a non-2xx, and a 404 counts as suspicious rather than as a refusal, since a fixture
id that stops resolving would otherwise pass forever. `NON_AUTHORIZATION_REFUSALS` and
`NOT_FOUND_IS_THE_GUARD` in that file explain the whole trap; both are empty, and adding to
either is meant to be a visible diff.

`bun run test:mutation` automates case 1 across the authorization and validation modules
listed in `stryker.config.json`. It is slow, so it is not part of `bun run check`, and CI
runs it weekly rather than on a push. Reach for it when you have written a batch of tests
and want to know which of them are decorative.

### A batch of new tests gets an adversarial review, by somebody else

**Rule: whoever wrote a batch of tests does not get to be the one who signs it off.** When
a change adds a meaningful number of tests (a new suite, or a set of them), a second
reviewer goes over them with one question in mind: _do these tests deliver what they claim
to?_ If the work is being done by agents, that reviewer is a separate agent with no stake
in the code it is reading.

This is not a style pass. The reviewer's job is to find:

- Tests that pass whether or not the production code works. Verify by mutation, do not take
  the author's word for it, and prefer a mutation the author did not already try.
- Assertions weak enough to survive the bug they were written for: `toBeTruthy()` on an
  object, a status code checked without checking the database row, a `403` with no `2xx`
  beside it, a `not.toThrow()` standing in for a real expectation.
- A test whose subject is the mock rather than the code. If every dependency is stubbed,
  ask what is left to be wrong.
- Coverage that reads as complete but is not: the happy path tested five ways and the
  rollback, the concurrent call and the failure branch tested not at all.
- Names that promise more than the body checks. The name is what the next person trusts.
- Setup so elaborate that the test no longer describes a situation the app can reach.

Two rounds of this have already been run on this suite and both found real problems, so it
is worth the cost. Findings go back to the author to fix; the reviewer does not quietly
rewrite the tests.

## Repo-specific conventions

- Use `auth()` from `@/lib/auth` for server-side session reads.
- Use `checkProjectAccess()` / `checkWorkspaceAccess()` for authorization instead of ad-hoc role checks.
- For API responses, use `successResponse` / `apiErrors` from `@/lib/api-response`.
- Keep API and UI imports on `@/` aliases when available.
- In Prisma raw SQL, use `$executeRaw` for statements that return no rows (e.g. `pg_advisory_xact_lock`). Using `$queryRaw` on void-returning functions causes a Prisma deserialization error (`Failed to deserialize column of type 'void'`).

## Important locations

- Custom SQL managed by Prisma migrations: `prisma/migrations/*/migration.sql`.
- Shared API response helpers: `lib/api-response.ts`.
- Auth + access-control helpers: `lib/auth.ts`.

## Change safety rules

- Prefer backward-compatible API changes unless explicitly asked to break contracts.
- For multi-step DB writes, use Prisma transactions.