refactor(#2267): golden-parity file-set snapshot + anti-staleness CI selection (#2274)

Phase 2 of golden-parity redesign (epic #2264). Adds an install file-set snapshot (golden-install-tree) and a ci-test-scope rule selecting golden-parity whenever any installed-source path changes, closing the silent-staleness hole behind the #2266 red. ADR-2264 amended (the copy/transform split premise was unsound). Closes #2267.

scripts/gen-install-tree-fixtures.cjs

@@ -0,0 +1,75 @@
+#!/usr/bin/env node
+'use strict';
+/**
+ * Standalone golden-fixture generator for tests/golden-install-tree (#2267 Phase 2).
+ *
+ * This is a BUILD-TIME generation script — NOT a test run. It imports the
+ * canonical buildInstallTree builder from tests/helpers/install-shared.cjs,
+ * which in turn reuses buildParityManifest's exact exclusion set (issue
+ * #2266) so the file-set fixtures here and the golden-install-parity content
+ * fixtures never diverge on which files they cover. The authoritative test
+ * gate remains `gsd-test run`, never a local `node --test`.
+ *
+ * Usage: node scripts/gen-install-tree-fixtures.cjs [runtime ...]
+ */
+const fs = require('node:fs');
+const path = require('node:path');
+const { execFileSync } = require('node:child_process');
+
+const ROOT = path.resolve(__dirname, '..');
+// buildInstallTree (and the exclusion constants it reuses from
+// buildParityManifest) is the canonical single source of truth in
+// tests/helpers/install-shared.cjs (issue #2266/#2267) — this generator does
+// not keep its own inline copy of the walk/exclusion logic.
+const { runMinimalInstall, RUNTIME_META, buildInstallTree, BUILD_SCRIPT } = require(path.join(ROOT, 'tests', 'helpers', 'install-shared.cjs'));
+const FIXTURE_DIR = path.join(ROOT, 'tests', 'fixtures', 'install-tree');
+
+function cleanup(root) {
+  try { fs.rmSync(root, { recursive: true, force: true }); } catch { /* best effort */ }
+}
+
+// Regenerate the fixture for every runtime in RUNTIME_META. Needed when a
+// SHARED gsd-core payload file (e.g. model-catalog.json, capability-registry)
+// changes content — its path appears in every runtime's manifest, so all
+// fixtures must be recaptured together. Usage:
+//   node scripts/gen-install-tree-fixtures.cjs [runtime ...]
+// With no args, regenerates ALL runtimes. With args, only the named runtimes.
+const targets = process.argv.slice(2).length > 0 ? process.argv.slice(2) : Object.keys(RUNTIME_META);
+fs.mkdirSync(FIXTURE_DIR, { recursive: true });
+
+// Build hooks/dist before capturing so fixtures are complete even in a clean
+// checkout (hooks/dist is gitignored + built; DEFECT.HOOKS-DIST-SCOPED-CI). The
+// test harness's before() hook does the same; without it a fresh checkout omits
+// every hooks/* path and this generator silently writes short fixtures.
+execFileSync(process.execPath, [BUILD_SCRIPT], { stdio: 'pipe' });
+
+for (const runtime of targets) {
+  if (!Object.prototype.hasOwnProperty.call(RUNTIME_META, runtime)) {
+    process.stderr.write(`[gen] unknown runtime '${runtime}' (not in RUNTIME_META) — skipping\n`);
+    continue;
+  }
+  const { configDir, root } = runMinimalInstall({ runtime, scope: 'global' });
+  let actual;
+  try {
+    actual = buildInstallTree(configDir, root);
+  } finally {
+    cleanup(root);
+  }
+  const fixturePath = path.join(FIXTURE_DIR, `${runtime}.json`);
+  fs.writeFileSync(fixturePath, JSON.stringify(actual, null, 2) + '\n', 'utf8');
+  process.stdout.write(`[gen] ${runtime}: wrote ${actual.length} paths -> ${fixturePath}\n`);
+}
+
+// Also regenerate the claude LOCAL legacy-layout fixture (claude-local.json).
+// This layout is distinct from the global install (commands/gsd-*.md +
+// agents/gsd-*.md) and has its own snapshot assertion in the test harness.
+const { configDir: localConfigDir, root: localRoot } = runMinimalInstall({ runtime: 'claude', scope: 'local' });
+let localActual;
+try {
+  localActual = buildInstallTree(localConfigDir, localRoot);
+} finally {
+  cleanup(localRoot);
+}
+const localFixturePath = path.join(FIXTURE_DIR, 'claude-local.json');
+fs.writeFileSync(localFixturePath, JSON.stringify(localActual, null, 2) + '\n', 'utf8');
+process.stdout.write(`[gen] claude-local: wrote ${localActual.length} paths -> ${localFixturePath}\n`);