Retire staged Yarn dependencies during Nix installation (#473)

PORTABLE_ARTIFACTS.md

@@ -69,6 +69,12 @@ describes its install-state file as an optimization cache in its
 This helper output is a dependency directory for a build, not a standalone
 Package or a runnable Yarn project. Its `devShell` supplies freestanding Yarn for
 editable projects; do not run Yarn against the readonly dependency output.
+Installation discards its disposable archive cache and streams dependencies into
+the output while retiring staged files, including across separate build/store
+mounts. It preserves package layout, native results, hidden data and executable
+links without holding two complete dependency trees. The maintained
+`camino-yarn-dependencies` check covers transfer and runtime layout; consuming
+Studio and Package-builder checks retain real locked-installation coverage.
 
 Use the shared `installDependencies` assembly for consumers: authored libraries
 are copied into the consumer's `node_modules`, where Node can find their

test/yarn-dependencies/yarn-project.nix

@@ -0,0 +1,31 @@
+# Tiny generated-project interface fixture. Real offline Yarn installation
+# remains covered by the consuming Studio and Package-builder checks.
+{ stdenvNoCC, nodejs }:
+{ src, overrideAttrs ? null }:
+let
+  project = stdenvNoCC.mkDerivation {
+    name = "yarn-dependencies-transfer-fixture";
+    inherit src;
+    configurePhase = ''
+      mkdir -p node_modules/fixture node_modules/.bin .yarn/cache
+      printf '%s\n' '{"main":"index.cjs"}' > node_modules/fixture/package.json
+      printf '%s\n' 'module.exports = {value: "retained dependency"};' > node_modules/fixture/index.cjs
+      ln node_modules/fixture/index.cjs node_modules/fixture/twin.cjs
+      ln -s fixture node_modules/alias
+      printf '%s\n' '#!${nodejs}/bin/node' 'console.log("linked executable");' > node_modules/fixture/cli.cjs
+      chmod +x node_modules/fixture/cli.cjs
+      ln -s ../fixture/cli.cjs node_modules/.bin/fixture
+      printf '%s\n' 'hidden dependency data' > node_modules/.fixture-data
+      printf '%s\n' 'disposable linker state' > node_modules/.yarn-state.yml
+      printf '%s\n' 'disposable archive' > .yarn/cache/fixture.zip
+    '';
+    postInstall = ''
+      test ! -e node_modules
+      test ! -e .yarn/cache
+      test ! -e "$out/.yarn-state.yml"
+      test ! -e "$out/node_modules"
+      test "$(stat -c %i "$out/fixture/index.cjs")" = "$(stat -c %i "$out/fixture/twin.cjs")"
+    '';
+  };
+in
+if overrideAttrs == null then project else project.overrideAttrs overrideAttrs

yarn-dependencies.nix

@@ -9,10 +9,18 @@ let
     overrideAttrs = _: {
       buildPhase = "runHook preBuild; runHook postBuild";
       installPhase = ''
+        set -o pipefail
         runHook preInstall
         test -d node_modules
+        test ! -L node_modules
         mkdir -p "$out"
-        cp -a node_modules/. "$out/"
+        # Installation is finished: retire its disposable archive cache, then
+        # stream dependencies across the build/store mount boundary without
+        # retaining a second complete tree. This is the same installation
+        # policy used by Central's dependency derivations.
+        rm -rf .yarn/cache
+        ${pkgs.gnutar}/bin/tar --create --file=- --remove-files node_modules \
+          | ${pkgs.gnutar}/bin/tar --extract --file=- --strip-components=1 --directory="$out"
         # Node resolves installed packages directly. This generated index is for
         # Yarn's linker, not a runtime input; do not export build-session state.
         rm -f "$out/.yarn-state.yml"

yarn-dependencies.test.nix

@@ -0,0 +1,24 @@
+{ pkgs }:
+let
+  dependencies = import ./yarn-dependencies.nix {
+    inherit pkgs;
+    src = ./test/yarn-dependencies;
+  };
+in
+pkgs.runCommand "quixos-yarn-dependencies-check" { nativeBuildInputs = [ pkgs.nodejs_24 ]; } ''
+  node - ${dependencies} <<'JS'
+  const assert = require('node:assert/strict');
+  const fs = require('node:fs');
+  const path = require('node:path');
+  const {execFileSync} = require('node:child_process');
+  const root = process.argv[2];
+  assert.deepEqual(require(path.join(root, 'fixture')), {value: 'retained dependency'});
+  assert.deepEqual(require(path.join(root, 'alias')), {value: 'retained dependency'});
+  assert.equal(fs.readlinkSync(path.join(root, 'alias')), 'fixture');
+  assert.equal(fs.readlinkSync(path.join(root, '.bin/fixture')), '../fixture/cli.cjs');
+  assert.equal(execFileSync(path.join(root, '.bin/fixture'), {encoding: 'utf8'}), 'linked executable\n');
+  assert.equal(fs.readFileSync(path.join(root, '.fixture-data'), 'utf8'), 'hidden dependency data\n');
+  assert.equal(fs.existsSync(path.join(root, '.yarn-state.yml')), false);
+  JS
+  touch "$out"
+''