# AGENTS.md

Guidance for AI coding agents working in this repository.

## Project

Next.js frontend for a Paradox save file parser. It uploads a game save file to a
backend service, polls until parsing finishes, and displays the result in a
grid.

- **Next.js 16** (App Router, Turbopack) with **React 19**
- **TypeScript 6 and 7** side by side (see "Things that will bite you"),
  **ESLint 9** (flat config), **Prettier 3**
- **ag-grid** for the data grid, **Bootstrap 5** for styling

Source files live in `src/`:

- `app/` for routes,
- `components/` for shared UI
- `services/` for backend calls
- `lib/` for helpers
- `config/` for app config
- `types/` for .d.ts type declaration files

## Architecture

The parsing backend is a **separate service in its own repository**, not part
of this project. Start it manually before running the frontend; it is expected
at `http://127.0.0.1:5226`.

The browser never calls that backend directly. Requests go through a Next route
handler that forwards them:

```
SaveParserBackendService  ->  /api/proxy/saveParserBackend/*  ->  backend
   (client, fetch)              (server, route handler)
```

- [src/services/SaveParserBackendService.ts](src/services/SaveParserBackendService.ts)
  is the only place that talks to the backend. It exposes `uploadSave`,
  `getSaveStatus` and `getParsedSave` — upload, poll until parsing finishes,
  then fetch the result.
- [src/app/api/proxy/saveParserBackend/[[...path]]/route.ts](src/app/api/proxy/saveParserBackend/[[...path]]/route.ts)
  forwards every method to the configured backend URL. It exists only to keep
  requests same-origin, and is meant to be deleted once the backend handles
  CORS itself.
- Route paths live in [src/app/api/proxy/paths.ts](src/app/api/proxy/paths.ts)
  rather than as string literals, so both sides of the proxy stay in sync.

Configuration comes from [src/config/AppConfig.ts](src/config/AppConfig.ts)
(defaults) merged with `runtimeConfig.json` at the repo root, which holds the
backend URL. That file is gitignored, so a fresh clone starts without one and
falls back to the defaults.

### Current status

Much of the app is still scaffold. Do not assume a feature works because the UI
for it exists:

- **The grid is not wired up.** [src/app/browse/page.tsx](src/app/browse/page.tsx)
  renders two hardcoded rows and never calls the backend. Nothing connects the
  upload flow to it yet.
- **Auth does not work.** `AuthService` posts to `/api/auth/login` and
  `/api/auth/register`, which do not exist as routes. The service is slated for
  removal in favour of Discord OAuth.
- **`hashPassword` is a no-op** that returns the password unchanged. Treat any
  current auth code as a placeholder, not as something to build on.

## Terminal

**On Windows, prefer `bash.exe`** — but only a real MSYS2, Cygwin, or
MinGW/Git Bash installation, for example `D:\msys2\usr\bin\bash.exe`.

**Never use `C:\Windows\System32\bash.exe`.** Despite its name it is not a
POSIX bash; it is the launcher stub for WSL. Do not start WSL to run ordinary
commands.

If no MSYS/Cygwin/MinGW bash is installed, **use PowerShell** as the terminal.
PowerShell is the fallback, never WSL.

If bash reports `command not found` for `node` or `npm`, that is a `PATH`
problem rather than a missing install: MSYS2 defaults `MSYS2_PATH_TYPE` to
`minimal`, which discards the Windows `PATH`. Setting it to `inherit` fixes it.

## Commands

```sh
npm run dev      # dev server
npm run build    # production build
npm run lint     # eslint
npm run format   # prettier, rewrites everything except .gitignore/.prettierignore
npx tsc --noEmit # typecheck
```

### Checking your work

**Always run `npm run lint` and `npm run build` after changing code.** They are
the primary way to find errors in this project, and they catch different
things:

- `npm run lint` reports code errors and style violations. It must finish with
  zero problems — no errors and no warnings.
- `npm run build` catches type errors and build-time problems that lint cannot
  see, such as Node APIs leaking into the edge runtime. It must exit cleanly
  and print no warnings.

`npx tsc --noEmit` is a faster way to check types alone while iterating, but it
does not replace a full build.

Do not report a change as finished until both commands pass.

## Version control

This project is managed with **git**.

**Read-only git commands are fine to use without asking.**
`git status`, `git log`, `git diff`, `git show`, `git blame` and similar inspection commands
may be run freely.

**Never run a git command that changes the repository without the user's
explicit permission.**
This is a strict ban, and it covers everything that writes to the history, the index,
or the working tree including `add`, `commit`, `checkout`, `restore`, `reset`,
`stash`, `branch`, `merge`, `rebase`, `push`, `rm`, etc.

Ask first and wait for a clear yes before running such git command.

## Conventions

Prettier settings live in `.prettierrc` and are not negotiable: **4 spaces, no
semicolons, single quotes, 80 column width**. Run `npm run format` after
editing, or match the surrounding style exactly.

Import from within `src/` using the `@/` alias, for example
`import { getMsgFromError } from '@/lib/errors'`.

Write doc comments as JSDoc (`/** ... */`), which editors show on hover.
Plain `//` and `///` comments do not appear in tooltips.
In `.ts` files put only prose in the JSDoc and let the signature carry the types;
do not duplicate types in `{braces}`.

Catch blocks should not annotate the error. Let it be `unknown` and convert it
with the shared helper:

```ts
} catch (err) {
    const errMsg = getMsgFromError(err)
    ...
}
```

Avoid `any`; `no-explicit-any` is enforced. Prefer `unknown` plus narrowing.

## Things that will bite you

**Both TypeScript 6 and 7 are installed on purpose, under swapped names.**
TypeScript 7 is the native Go compiler and type-checks much faster, but
typescript-eslint refuses to run under it, which would break `npm run lint`
entirely. So each tool gets the version it can use:

| package.json entry   | resolves to                                      | used by           |
| -------------------- | ------------------------------------------------ | ----------------- |
| `typescript`         | `@typescript/typescript6` (TS 6 API, bin `tsc6`) | typescript-eslint |
| `@typescript/native` | `typescript@7` (Go compiler)                     | `next build`      |

The alias is deliberately reversed: typescript-eslint looks the compiler up by
the package _name_ `typescript`, so that name must stay on TS 6. Do not "fix"
this by renaming the entries.

`next.config.ts` sets `experimental.useTypeScriptCli`, which makes Next spawn a
`tsc` binary instead of using the compiler API. Next resolves that binary from
the package named `typescript` too, so it would also get TS 6. The `prebuild`
script [scripts/replace-tsc6-with-tsc7.mjs](scripts/replace-tsc6-with-tsc7.mjs)
works around this by rewriting `node_modules/typescript/bin/tsc6` into a
one-line stub that imports TS 7's `lib/tsc.js`.

Consequences to keep in mind:

- The patch lives in `node_modules`, so `npm install` undoes it. `prebuild`
  reapplies it, so `npm run build` is always correct; nothing else needs doing.
- `npx tsc --noEmit` is unaffected either way. `node_modules/.bin/tsc` links
  straight to `@typescript/native`, so the standalone typecheck is always TS 7.
- Do not drop the `prebuild` script while leaving `useTypeScriptCli` enabled.
  Nothing breaks visibly — the build just silently goes back to type-checking
  with TS 6.

**All of this is temporary.** The only reason TS 6 is still here is that
TypeScript 7.0 ships no stable programmatic JS API, so typescript-eslint cannot
run on it. That API arrives in **TypeScript 7.1, planned for 2026-11-24**. Once
it is out and typescript-eslint supports it, tear the whole arrangement down:
drop `@typescript/native` and the `@typescript/typescript6` alias for a plain
`"typescript": "^7.1"`, delete `scripts/replace-tsc6-with-tsc7.mjs` and the
`prebuild` script, and re-check whether `useTypeScriptCli` is still worth
keeping.

**Env vars in npm scripts must go through `cross-env`.** The `dev` and `build`
scripts set `NEXT_TELEMETRY_DISABLED=1`, which stops Next from collecting
anonymous usage data and saves the ~0.5s the telemetry flush adds to every
build. The `FOO=1 cmd` prefix is POSIX shell syntax, and on Windows npm runs
scripts through `cmd`, where it is a syntax error — so the prefix is written as
`cross-env NEXT_TELEMETRY_DISABLED=1 next ...` instead. Keep `cross-env` on any
new script that needs an env var.

Setting the variable from `prebuild` would not work: `prebuild` and `build` are
sibling processes, so an env var exported by one is not visible to the other.
Each script that needs it sets it itself. `prebuild` has no `cross-env` prefix
because it only rewrites the tsc bin and never talks to telemetry.

**`instrumentation.ts` is compiled for the edge runtime too and it can't be disabled.**
Anything using `fs`, `path`, or other Node APIs must be imported behind the
`process.env.NEXT_RUNTIME === 'nodejs'` guard, or the build warns and pulls
Node-only code into the edge bundle.