Add xteink fork dev tooling (native flake devShell + README)

README.xteink.md

@@ -0,0 +1,39 @@
+# xteink QEMU fork
+
+Espressif's QEMU fork carrying the xteink X3/X4 (ESP32-C3) machine model and a
+wasm32 TCG backend (ported from [ktock/qemu-wasm](https://github.com/ktock/qemu-wasm)),
+used by [xteink-web-emulator](../xteink-web-emulator) to run CrossPoint firmware
+in the browser.
+
+## Branch
+
+- `main` — the working branch. Base is Espressif's `esp-develop-9.2.2-20260417`
+  (`40edccac`).
+
+## Remotes
+
+- `origin` — https://ssh.gitea.va.reichard.io/evan/qemu-xteink
+- `upstream` — https://github.com/espressif/qemu
+- `qemu-wasm` — https://github.com/ktock/qemu-wasm (source of the wasm32 backend)
+
+## Building
+
+### Native (parity check — authoritative)
+
+```sh
+nix develop
+./configure --target-list=riscv32-softmmu --with-devices-riscv32=xteink --enable-gcrypt
+ninja -C build qemu-system-riscv32
+```
+
+### WebAssembly
+
+Driven by the parent repo, not here:
+
+```sh
+cd ../xteink-web-emulator
+make web-dev     # incremental build straight from this tree
+```
+
+The parent's `scripts/build-qemu-wasm.sh` compiles this checkout inside the
+emsdk Docker image defined in `xteink-web-emulator/qemu/wasm/Dockerfile`.

flake.nix

@@ -0,0 +1,40 @@
+{
+  description = "Espressif QEMU fork with the xteink X3/X4 (ESP32-C3) machine and a wasm32 TCG backend";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs =
+    { self, nixpkgs, flake-utils }:
+    flake-utils.lib.eachDefaultSystem (
+      system:
+      let
+        pkgs = nixpkgs.legacyPackages.${system};
+      in
+      {
+        # Native build/test shell. The wasm target is built by the parent
+        # xteink-web-emulator repo via its emsdk Docker toolchain, not here.
+        #
+        #   nix develop
+        #   ./configure --target-list=riscv32-softmmu --with-devices-riscv32=xteink \
+        #     --enable-gcrypt && ninja -C build qemu-system-riscv32
+        devShells.default = pkgs.mkShell {
+          inputsFrom = [ pkgs.qemu ];
+          packages = with pkgs; [
+            gnumake
+            git
+            ninja
+            meson
+            pkg-config
+            libgcrypt
+            libslirp
+            pixman
+            dosfstools
+            mtools
+          ];
+        };
+      }
+    );
+}