> For the complete documentation index, see [llms.txt](https://docs.kouch.dev/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.kouch.dev/docs/adr/0012-emulation-folder-layout.md).

# ADR 0012: EmuDeck-compatible, multi-disk Emulation folder; cloud-safe data per Steam user

## Status

Accepted on 2026-09-26. This supersedes where ADR 0007 stored data (`Settings.user_data_root` and `<data>/emulators`).

## Context

The owner's PC already has an EmuDeck-style `Emulation` folder:

* `bios`
* `roms/<system>`
* `saves/<emu>`
* `storage/<emu>`
* `storage/downloaded_media`
* `tools`

The owner wants:

* a first-run step that asks which disk to create the folder on, like EmuDeck
* support for multiple disks, with one main disk for the central data
* cloud-safe data kept in Steam's per-user cloud folder

## Decision

* **Main disk.** `<disk>\Emulation\` holds:
  * `bios`
  * `roms`
  * `saves`
  * `storage`
  * `storage\downloaded_media`
  * `tools\kouch`
  * `emulators` (Kouch addition)
  * `mods` (Kouch addition)
* **Extra disks.** They use the same `roms\<system-folder>` layout.
* **Folder names come from profiles** (schema v2 `folder` and `data_folder`). Kouch's code contains no system names.
* **`storage::ensure_layout()` is idempotent and only ever creates.** It never moves, renames or deletes existing files.
  * An existing tree is adopted in place.
  * Any change to an emulator's paths is shown as a preview and must be confirmed first.
* **Saves live per Steam user.** `saves\<emu>` is a directory junction into the active Steam user's cloud folder, `<Steam>\userdata\<account>\<app id>\remote\`.
  * If Steam turns out not to sync files placed there directly, the junction points at `%APPDATA%\kouch\cloud\<steam id>` instead, and `cloud.rs` syncs it.
  * Moving existing saves in is opt-in, backed up first, and restorable.
* **`bios` is never touched.** It is created empty, with a readme. Kouch never reads, syncs or sends it (ground rule 2).

## Consequences

* A migration moves today's `%LOCALAPPDATA%\kouch\emulators` and `userdata` into the new tree.
* Development and tests never modify the owner's real `R:\Emulation`. They use temp directories and a scratch copy.


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