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

.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.test.ts

@@ -57,4 +57,13 @@ describe('executeBundleUIStep', () => {
     // Then
     expect(fs.copyFile).toHaveBeenCalledWith('/test/extension/dist', '/bundle/handle')
   })
+
+  test('skips the copy when local and bundle output directories resolve to the same path but differ as strings', async () => {
+    mockContext.extension.outputPath = '/test/./extension/dist/handle.js'
+    vi.mocked(buildExtension.buildUIExtension).mockResolvedValue('/test/extension/dist/handle.js')
+
+    await executeBundleUIStep(step, mockContext)
+
+    expect(fs.copyFile).not.toHaveBeenCalled()
+  })
 })

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)
   }