Normalize paths in bundle-ui-step same-path guard

The same-path guard at bundle-ui-step.ts compared `localOutputDir` and
`bundleOutputDir` as raw strings. In practice these two values are
computed along different code paths (`dirname(buildUIExtension())` vs
`dirname(extension.outputPath)` or `joinPath(..., bundleFolder)`) and
can resolve to the same filesystem directory while differing as strings
— e.g. when one path has a `.` segment, a trailing slash, or otherwise
non-canonical shape. When that happens, the guard slips through and
fs-extra rejects the copy with "Source and destination must not be the
same".

Normalize both sides via `resolvePath` before comparing so the guard
catches any string variant that maps to the same directory.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: vctrchu

.changeset/fix-bundle-ui-step-path-normalization.md

@@ -0,0 +1,5 @@
+---
+'@shopify/app': patch
+---
+
+Fix `shopify app build` intermittently failing with "Source and destination must not be the same" on UI extensions when the local esbuild output directory and the bundle output directory resolve to the same path but differ as strings (e.g. due to `.` segments, trailing slashes, or path joining quirks). The same-path guard now normalizes both paths via `resolvePath` before comparison.

packages/app/src/cli/services/build/steps/bundle-ui-step.ts

@@ -2,7 +2,7 @@ import {createOrUpdateManifestFile} from './include-assets/generate-manifest.js'
 import {buildUIExtension} from '../extension.js'
 import {BuildManifest} from '../../../models/extensions/specifications/ui_extension.js'
 import {copyFile} from '@shopify/cli-kit/node/fs'
-import {dirname, joinPath} from '@shopify/cli-kit/node/path'
+import {dirname, joinPath, resolvePath} from '@shopify/cli-kit/node/path'
 import type {BundleUIStep, BuildContext} from '../client-steps.js'
 
 interface ExtensionPointWithBuildManifest {
@@ -27,7 +27,7 @@ export async function executeBundleUIStep(step: BundleUIStep, context: BuildCont
   const bundleOutputDir = step.config?.bundleFolder
     ? joinPath(dirname(context.extension.outputPath), step.config.bundleFolder)
     : dirname(context.extension.outputPath)
-  if (localOutputDir !== bundleOutputDir) {
+  if (resolvePath(localOutputDir) !== resolvePath(bundleOutputDir)) {
     await copyFile(localOutputDir, bundleOutputDir)
   }