docs(switch): add switch-build contributor guide

Co-authored-by: Cursor <cursoragent@cursor.com>

docs/switch-build.md

@@ -0,0 +1,155 @@
+# Build the Nintendo Switch NRO — contributor guide
+
+Want to play a release build instead? Download the fused NRO and copy it to
+your console — see [switch-install.md](switch-install.md).
+
+This guide is for contributors who build Gen1Recomp for Switch from source.
+Hardware evidence, MTP operator loops, and deeper WIP notes live in
+[switch-development.md](switch-development.md).
+
+> **Experimental.** Releases may ship a fused `gen1recomp-*-switch.nro`, but
+> the port is still WIP (issue
+> [#531](https://github.com/bryanthaboi/gen1recomp/issues/531)). Hardware
+> evidence so far is **Switch OLED only**.
+
+---
+
+## Prerequisites by OS
+
+All packaging entrypoints are **bash**. On Windows, use Git Bash, MSYS2, or
+WSL — not cmd.exe or PowerShell (AD-008).
+
+### macOS / Linux
+
+1. Install [devkitPro pacman](https://devkitpro.org/wiki/devkitPro_pacman).
+2. Install Switch tools:
+
+   ```sh
+   sudo dkp-pacman -S switch-dev
+   ```
+
+3. Ensure `nacptool` and `elf2nro` are on `PATH` (or under
+   `$DEVKITPRO/tools/bin` — the fused script prepends that when set).
+
+**Optional:** Install [Docker](https://docs.docker.com/get-docker/) so fused
+builds can fall back to the pinned image when native tools are missing.
+
+### Windows (Git Bash / MSYS2 / WSL)
+
+1. Use a bash environment:
+   - **MSYS2** with the [devkitPro](https://devkitpro.org/wiki/devkitPro_pacman)
+     packages (preferred for native `nacptool`/`elf2nro`), or
+   - **WSL** (Ubuntu/etc.) with the Linux pacman flow above, or
+   - **Git Bash** for `--fetch` / `--loose`; for `--fused` prefer MSYS2 or
+     WSL if Docker bind-mounts from Git Bash paths misbehave.
+2. Install `switch-dev` (or rely on Docker fallback — see below).
+3. Do **not** expect `scripts/build_switch.sh` to run under cmd/PowerShell.
+
+### What you must install yourself
+
+| You install | Script does **not** install |
+| ----------- | --------------------------- |
+| bash, git, zip tooling the repo already expects | — |
+| `dkp-pacman` + `switch-dev` (native fused) | `dkp-pacman -S …` |
+| Docker (optional fused fallback) | Docker Engine |
+| A legal `.gb` ROM (to play) | Any ROM or game data |
+
+---
+
+## Mode glossary
+
+`scripts/build_switch.sh` supports three modes (combinable as noted):
+
+| Mode | What it does |
+| ---- | ------------ |
+| `--fetch` | Downloads pinned **love.nro** + **love.elf** into `.bazinga/love-nx/11.5-nx1/` and verifies SHA-256 against `scripts/switch/love-nx-11.5-nx1.sha256`. |
+| `--loose` | Packs `game.love`, copies pinned `love.nro` → `dist/switch/loose/` as `gen1recomp.nro` + `game.love` side by side. Needs the pin. |
+| `--fused` | Builds a single `dist/switch/gen1recomp-<ver>-switch.nro` (game in romfs) via `nacptool` + `elf2nro`. Needs the pin + toolchain (native or Docker). |
+
+Rules:
+
+- `--fetch` alone is fine; combine as `--fetch --loose` or `--fetch --fused`.
+- `--loose` and `--fused` are **XOR** — pick one packaging path per run.
+- `--version X.Y.Z` sets the NACP / filename version (defaults to short git SHA).
+
+### What `--fetch` downloads
+
+Only the two pinned love-nx release assets (`love.nro`, `love.elf`). It does
+**not** install:
+
+- devkitPro / `dkp-pacman` / `switch-dev`
+- Docker
+- ROMs, saves, or mods
+
+---
+
+## Native tools, then Docker
+
+Fused packaging (`scripts/switch/build_fused.sh`):
+
+1. Prefer native `nacptool` + `elf2nro` on `PATH` (or `$DEVKITPRO/tools/bin`).
+2. Else fall back to Docker using:
+   - `GEN1_DKP_IMAGE` if set, otherwise
+   - the image named in `scripts/switch/dkp-docker.image` (default
+     `devkitpro/devkita64:latest`).
+
+If neither native tools nor Docker work, the script exits non-zero with
+macOS / Linux / Windows / Docker hints and a pointer to this doc.
+
+---
+
+## Example commands
+
+From the repo root:
+
+```sh
+# Download pinned love-nx only
+scripts/build_switch.sh --fetch
+
+# Loose pair for iteration (fetch + assemble)
+scripts/build_switch.sh --fetch --loose
+
+# Single fused NRO for a release-like artifact
+scripts/build_switch.sh --fetch --fused --version 0.2.0
+```
+
+Outputs land under `dist/switch/` (and `dist/switch/loose/` for loose mode).
+The fused path also writes `gen1recomp-<ver>-switch.nro.sha256`.
+
+Offline packaging smoke (no network, no nacptool required):
+
+```sh
+bash scripts/switch/selftest_build_switch.sh
+bash scripts/switch/verify_payload.sh --self-test
+```
+
+---
+
+## Release Mac runner
+
+GitHub Releases build the Switch artifact on the same self-hosted Mac runner
+as the other platforms (see `.github/workflows/release.yml`):
+
+```sh
+scripts/build_switch.sh --fetch --fused --version "<release version>"
+```
+
+The runner must have **native switch-tools** (`nacptool`/`elf2nro`) **and/or
+Docker** available. CI does not silently run `dkp-pacman -S`; keep the runner
+image/host provisioned per this guide.
+
+---
+
+## Limitations / non-goals
+
+These scripts and this guide do **not**:
+
+- Push files to the console (no MTP / OpenMTP / DBI automation)
+- Bundle or download any Pokémon ROM
+- Install `dkp-pacman` / `switch-dev` for you
+- Provide `nxlink` / netloader deploy
+- Validate **Applet Mode** — use title override (hold **R**) for full memory
+
+Player install steps: [switch-install.md](switch-install.md).  
+Hardware depth and evidence: [switch-development.md](switch-development.md),
+[switch-hardware-evidence.md](switch-hardware-evidence.md).