feat: Add Nix flake support

docs/operations/development.md

@@ -15,6 +15,18 @@ a new browser.
 
 Prefer a container? See [Dev container](../internals/devcontainer.md) for VS Code and Codespaces setup.
 
+### Nix
+
+A `flake.nix` at the repo root provides a dev shell with the toolchain matching CI
+(Node 24, pnpm, Rust stable, and the Linux desktop build prerequisites). With Nix and
+flakes enabled:
+
+```sh
+nix develop
+```
+
+Install the `vp` task runner once (it is not in nixpkgs); the shell prints the command if it is missing. After installing it, exit and re-enter `nix develop`, then `vp i` and `vp run dev` work as above. Regenerate `flake.lock` with `nix flake lock` when bumping the pinned nixpkgs revision.
+
 ## Choosing a dev process
 
 Use `vp run dev` for server and web, or `vp run dev:desktop` for the Electron client.

flake.nix

@@ -0,0 +1,72 @@
+{
+  description = "T3 Code development shell";
+
+  inputs = {
+    # nixpkgs-unstable branch; the resolved revision is pinned by flake.lock.
+    # Regenerate with: nix flake lock   (or bump with: nix flake update nixpkgs)
+    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+  };
+
+  outputs =
+    { nixpkgs, ... }:
+    let
+      forAllSystems =
+        function:
+        nixpkgs.lib.genAttrs nixpkgs.lib.systems.flakeExposed (
+          system: function nixpkgs.legacyPackages.${system}
+        );
+    in
+    {
+      formatter = forAllSystems (pkgs: pkgs.alejandra);
+
+      devShells = forAllSystems (
+        pkgs:
+        let
+          inherit (pkgs) lib;
+        in
+        {
+          default = pkgs.mkShell {
+            packages =
+              with pkgs;
+              [
+                # Node 24 (engines.node in package.json) + pnpm for `vp i`.
+                nodejs_24
+                pnpm
+
+                # The `vp` repo task runner (installed separately, see below).
+                # Rust stable: native/resource-monitor (cargo fmt + test run in CI).
+                cargo
+                rustc
+                rustfmt
+                clippy
+
+                # node-gyp fallback for node-pty (its prebuilds are mac/win only).
+                python3
+                gnumake
+              ]
+              ++ lib.optionals stdenv.hostPlatform.isLinux [
+                gcc
+                pkg-config
+                # browser-secret helper links against the host's libsecret.
+                libsecret
+                imagemagick
+              ]
+              ++ lib.optionals stdenv.hostPlatform.isDarwin [
+                # clang toolchain for node-gyp on macOS.
+                clang
+              ];
+
+            # The Vite+ CLI (`vp`) is not packaged in nixpkgs. Install it once:
+            #   curl -fsSL https://vite.plus | bash
+            # with VP_NODE_MANAGER=no so it reuses this shell's Node.
+            shellHook = ''
+              if ! command -v vp >/dev/null 2>&1; then
+                echo "note: 'vp' not found. Install it with:" >&2
+                echo "  curl -fsSL https://vite.plus | VP_NODE_MANAGER=no bash" >&2
+              fi
+            '';
+          };
+        }
+      );
+    };
+}