feat(amplify-gen2-migration-e2e-system): add decommission step to

E2E migration flow

Wire `gen2-migration decommission` into `App.migrate()` so the
E2E system exercises the full migration lifecycle including Gen1
teardown. After the final `testSharedData()`, the flow checks out
the Gen1 branch, runs `amplifyPullNonInteractive` to restore
`amplify-meta.json` (which is gitignored and missing after branch
switch), then runs `decommission` and verifies the Gen2 app still
works via `testGen2()`.

The `decommission()` method follows the same pattern as the
existing `refactor()` — delegates to `runMigrationStep()` with
no extra args. The `amplifyPullNonInteractive` call reads the
appId from `team-provider-info.json` (which is tracked in git).

Apps with `skipRefactor=true` are unaffected since the new calls
live after the early return in `migrate()`.

E2E runs confirmed the wiring works: `backend-only` and
`store-locator` completed the full flow including decommission
and post-decommission `testGen2`.
---
Prompt: Add decommission step to E2E migration flow after
refactor, followed by testGen2() to verify the Gen2 app is
self-contained after Gen1 teardown. Run E2Es on all 9 apps
in parallel.

Author: sai-ray

packages/amplify-gen2-migration-e2e-system/src/core/app.ts

@@ -2,7 +2,7 @@ import execa from 'execa';
 import fs from 'fs-extra';
 import path from 'path';
 import os from 'os';
-import { getCLIPath, initJSProjectWithProfile } from '@aws-amplify/amplify-e2e-core';
+import { getCLIPath, initJSProjectWithProfile, amplifyPullNonInteractive } from '@aws-amplify/amplify-e2e-core';
 import { Logger, LogLevel } from './logger';
 import { Git } from './git';
 import * as snapshot from './snapshot';
@@ -276,6 +276,11 @@ export class App {
     await this.testGen2();
 
     await this.testSharedData();
+
+    await this.git.checkout(this.gen1BranchName, false);
+    await amplifyPullNonInteractive(this.targetAppPath, { appId: this.getAmplifyAppId(), envName: this.envName });
+    await this.decommission();
+    await this.testGen2();
   }
 
   /**
@@ -301,6 +306,13 @@ export class App {
     this.removeGitignoreLine('amplify_outputs*');
   }
 
+  /**
+   * Run `amplify gen2-migration decommission` to tear down the Gen1 environment.
+   */
+  public async decommission(): Promise<void> {
+    await this.runMigrationStep('decommission');
+  }
+
   /**
    * Run `amplify gen2-migration refactor`.
    */
@@ -460,6 +472,16 @@ export class App {
     return JSON.parse(fs.readFileSync(configPath, 'utf-8')) as MigrationConfig;
   }
 
+  private getAmplifyAppId(): string {
+    const tpiPath = path.join(this.targetAppPath, 'amplify', 'team-provider-info.json');
+    const tpi = JSON.parse(fs.readFileSync(tpiPath, 'utf-8')) as Record<string, Record<string, Record<string, string>>>;
+    const appId = tpi[this.envName]?.awscloudformation?.AmplifyAppId;
+    if (!appId) {
+      throw new Error(`AmplifyAppId not found in team-provider-info.json for env ${this.envName}`);
+    }
+    return appId;
+  }
+
   private async runAmplify(args: string[], options?: { stdio?: 'inherit' }): Promise<void> {
     const originalCwd = process.cwd();
     process.chdir(this.targetAppPath);