fix(#2116): use resolvable paths in surface.md require + correct package name

Four require() examples in commands/gsd/surface.md used bare
'gsd-core/...' specifiers that Node cannot resolve (wrong package
name + runtime-mirror layout off module path). Now derives the path
from runtimeConfigDir. Also fixes reinstall hint from
'npm i -g gsd-core' to 'npm i -g @opengsd/gsd-core'.

tests/surface-md-paths.regression.test.cjs

@@ -0,0 +1,41 @@
+/**
+ * Regression test for #2116 — commands/gsd/surface.md had unresolvable bare
+ * `require('gsd-core/...')` specifiers and a wrong-package reinstall hint
+ * (`npm i -g gsd-core` instead of `@opengsd/gsd-core`).
+ *
+ * This test asserts the doc uses resolvable paths (derived from runtimeConfigDir)
+ * and the correct scoped package name in the reinstall hint.
+ */
+'use strict';
+
+const { describe, test } = require('node:test');
+const assert = require('node:assert/strict');
+const fs = require('fs');
+const path = require('path');
+
+const SURFACE_MD = path.join(__dirname, '..', 'commands', 'gsd', 'surface.md');
+
+describe('#2116 regression: surface.md resolvable require + correct package', () => {
+  const content = fs.readFileSync(SURFACE_MD, 'utf-8');
+
+  test('no bare require("gsd-core/...") specifiers', () => {
+    assert.ok(
+      !content.match(/require\s*\(\s*['"]gsd-core\//),
+      'surface.md should not use bare require(\'gsd-core/...\') — use runtimeConfigDir-derived path (#2116)'
+    );
+  });
+
+  test('reinstall hint uses scoped package name', () => {
+    assert.ok(
+      content.includes('@opengsd/gsd-core'),
+      'surface.md reinstall hint should reference @opengsd/gsd-core, not bare gsd-core (#2116)'
+    );
+  });
+
+  test('require examples use runtimeConfigDir-derived paths', () => {
+    assert.ok(
+      content.includes("require(runtimeConfigDir + '/gsd-core/bin/lib/capability-registry.cjs')"),
+      'surface.md require examples should derive the path from runtimeConfigDir (#2116)'
+    );
+  });
+});