feat(devshells): add vtimeline devshell for the VeeamTimelineView project

Sister project at S:\Git\VeeamTimelineView has its own repo and gitea

remote; we keep its Nix env here in the home-fleet flake so the project

itself stays free of Nix.

`nix develop .#vtimeline` provides:

  - nodejs_22 (Node 20 hit EOL 2026-04-30 and was removed from nixpkgs)

  - python3 (Playwright webServer)

  - chromium (used via PLAYWRIGHT_BROWSERS_PATH symlink farm, since

    Playwright 1.40+ hard-codes a separate chrome-headless-shell path)

Shell banner points at ../VeeamTimelineView. The absolute project path

cannot be baked into the shellHook (Nix forbids escaping the flake source

dir at eval time); user is expected to `cd` themselves.

devshells/default.nix

@@ -0,0 +1,77 @@
+# Per-project devshells. Each entry here is a self-contained mkShell that
+# can be entered with `nix develop .#<name>`.
+#
+# Why this lives in the nixos flake:
+#   vtimeline is a sibling project under /s/Git/VeeamTimelineView (not part
+#   of the NixOS configs). Keeping its devshell here avoids polluting the
+#   project itself with a flake, while still letting us `nix develop` into
+#   the same node/python/chromium toolchain that NixOS uses.
+{ inputs, ... }@_flakeContext:
+let
+  system = "x86_64-linux";
+  pkgs = import inputs.nixpkgs {
+    inherit system;
+    config = { allowUnfree = true; };
+  };
+in
+{
+  devShells.${system} = {
+    # `nix develop .#vtimeline` -> shell for testing the VeeamTimelineView
+    # project (Playwright + ESLint + Prettier over a vanilla-JS frontend).
+    vtimeline = pkgs.mkShell {
+      name = "vtimeline-devshell";
+
+      buildInputs = with pkgs; [
+        # nodejs_20 was removed from nixpkgs on 2026-07-13 after Node.js 20
+        # reached upstream EOL on 2026-04-30. nodejs_22 is the current LTS.
+        # VeeamTimelineView's package.json does not pin a Node version, so
+        # this is transparent to npm.
+        nodejs_22
+        python3
+        chromium
+      ];
+
+      # `nodePackages.*` deliberately not added — they would pollute the
+      # shell globally. Anything npm-side goes through `npm install` in the
+      # project's own node_modules.
+
+      shellHook = ''
+        # Skip Playwright's own browser download — we use the system one.
+        export PLAYWRIGHT_SKIP_BROWSER_DOWNLOAD=1
+
+        # Direct executable-path override (honoured by older Playwright and
+        # the `channel: "chromium"` code path).
+        export PLAYWRIGHT_CHROMIUM_EXECUTABLE_PATH=${pkgs.chromium}/bin/chromium
+
+        # Playwright 1.40+ uses a separate "chrome-headless-shell" binary
+        # in headless mode and looks for it under a hard-coded path
+        # ($PLAYWRIGHT_BROWSERS_PATH/chromium_headless_shell-<rev>/...).
+        # We satisfy that lookup by symlinking the nixpkgs chromium into a
+        # fake registry directory.
+        export NIX_CHROMIUM=${pkgs.chromium}/bin/chromium
+        export PLAYWRIGHT_BROWSERS_PATH=$HOME/.cache/vtimeline-pw-browsers
+        mkdir -p "$PLAYWRIGHT_BROWSERS_PATH"
+        link_bin() {
+          local d="$PLAYWRIGHT_BROWSERS_PATH/$1"
+          mkdir -p "$d"
+          ln -sfn "$NIX_CHROMIUM" "$d/chrome-headless-shell"
+          ln -sfn "$NIX_CHROMIUM" "$d/chrome"
+        }
+        # Layouts derived from Playwright's EXECUTABLE_PATHS table for
+        # the chromium + chromium-headless-shell entries (linux-x64).
+        link_bin "chromium-1248/chrome-linux"
+        link_bin "chromium_headless_shell-1248/chrome-headless-shell-linux64"
+
+        # Convenience banner. The VeeamTimelineView project lives next to
+        # this flake repo (../VeeamTimelineView from the nixos checkout,
+        # i.e. S:\\Git\\VeeamTimelineView on Windows). We don't bake the
+        # path into the shellHook because Nix forbids escaping the flake
+        # source dir at eval time — print a hint and let the user `cd`.
+        echo "[vtimeline-devshell] node:   $(command -v node)"
+        echo "[vtimeline-devshell] python: $(command -v python3)"
+        echo "[vtimeline-devshell] chrome: $NIX_CHROMIUM"
+        echo "[vtimeline-devshell] run:    cd ../VeeamTimelineView && npm install && npm test"
+      '';
+    };
+  };
+}