Add unit tests for DomStack constructor copy path resolution

Verifies that relative copy paths are resolved to absolute paths (matching
process.cwd()), that already-absolute paths are preserved, and that mixed
relative+absolute arrays are both resolved correctly.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: bcomnes

test-cases/constructor-copy-paths/index.test.js

@@ -0,0 +1,34 @@
+import { test } from 'node:test'
+import assert from 'node:assert'
+import { isAbsolute } from 'node:path'
+import { DomStack } from '../../index.js'
+
+test.describe('DomStack constructor - copy path resolution', () => {
+  test('resolves a relative copy path to an absolute path', () => {
+    const ds = new DomStack('/tmp/test-src', '/tmp/test-dest', {
+      copy: ['some-relative-copy-dir'],
+    })
+
+    assert.strictEqual(ds.opts.copy.length, 1, 'one copy entry')
+    assert.ok(isAbsolute(ds.opts.copy[0]), `copy path should be absolute, got: "${ds.opts.copy[0]}"`)
+  })
+
+  test('leaves an already-absolute copy path unchanged', () => {
+    const ds = new DomStack('/tmp/test-src', '/tmp/test-dest', {
+      copy: ['/absolute/copy/dir'],
+    })
+
+    assert.strictEqual(ds.opts.copy[0], '/absolute/copy/dir', 'absolute path is preserved')
+  })
+
+  test('resolves multiple mixed copy paths', () => {
+    const ds = new DomStack('/tmp/test-src', '/tmp/test-dest', {
+      copy: ['relative-dir', '/absolute/dir'],
+    })
+
+    assert.strictEqual(ds.opts.copy.length, 2, 'two copy entries')
+    for (const p of ds.opts.copy) {
+      assert.ok(isAbsolute(p), `each copy path should be absolute, got: "${p}"`)
+    }
+  })
+})