fix(gen2-migration): skip Identity Pool when Gen1 auth is User Pool-only

[sharonyajain]

Problem

When migrating a Gen1 Amplify project to Gen2 using amplify gen2-migration generate, the migration tool creates Identity Pool configuration even when the Gen1 project was configured with "User Sign-Up & Sign-In only" — which provisions only a Cognito User Pool with no Identity Pool dependency.

This changes the auth architecture from JWT-based (User Pool authorizer) to IAM-based (which requires an Identity Pool), creates orphaned IAM roles, and breaks ampx generate outputs if the Identity Pool is later removed via CDK escape hatches.

Closes #14742

Root Cause

auth.generator.ts unconditionally called this.gen1App.resourceMetaOutput(this.resource, 'IdentityPoolId') which throws if the key is absent. Even when present (Gen1 always creates an Identity Pool), the renderer emitted Identity Pool escape-hatch code without checking whether the pool was actually in use.

Changes

• gen1-app.ts: Add tryResourceMetaOutput() — a non-throwing variant that returns undefined for absent output keys
• auth.generator.ts: Use tryResourceMetaOutput for IdentityPoolId; skip fetchIdentityPool when absent
• auth.renderer.ts: Guard all Identity Pool escape hatches (cfnIdentityPool, cognitoIdentityProviders push, addPropertyDeletionOverride) on !!options.identityPool
• auth.generator.test.ts: Add regression test for User Pool-only configuration (no IdentityPoolId in output)

Testing

• New test: generates auth without Identity Pool when IdentityPoolId is absent
• Verifies fetchIdentityPool is never called
• Verifies generated code contains no cfnIdentityPool, cognitoIdentityProviders, or cognitoProviders references
• Existing tests still pass (they all provide IdentityPoolId in their meta)

[sharonyajain]

CI Failure Note

The build-and-test check failure is a pre-existing repo-wide issue unrelated to this PR's changes. The same failure reproduces on other PRs (e.g. feat/gen2-migration-non-js-functions — run 32198932303).

Root cause

GitHub Actions recently deprecated Node 20 on runners and forces all actions to run under Node 24. Under Node 24, Jest's process exit behavior is stricter with open async handles — specifically Socket listeners from AWS SDK client mocks in the gen2-migration snapshot tests prevent cli-internal from exiting cleanly (exit code 1 from open handles, not from test failures).

All cli-internal test suites PASS (including the new regression test added in this PR). The exit code 1 comes from Jest being unable to shut down the process after tests complete.

What this PR includes to mitigate

• SpinningLogger singleton SIGINT handler — fixes the MaxListenersExceededWarning: 11 SIGINT listeners accumulation (each SpinningLogger instance was registering a new handler; now uses a static singleton pattern)
• --forceExit --detectOpenHandles on the cli-internal test script — matches the pattern already used by amplify-appsync-simulator and amplify-provider-awscloudformation in this repo

What remains (out of scope for this PR)

The Node 24 runner upgrade requires either:

1. Fixing the remaining Socket handle leaks in the AWS SDK mock clients used by gen2-migration tests, OR
2. Adding timeout-minutes to the workflow, OR
3. Splitting the cli-internal test suite into shards

This blocks all PRs to this repo equally and should be tracked as a separate infrastructure issue.

[sarayev]

The destination branch should be dev, main is for releases. See here: https://github.com/aws-amplify/amplify-cli/blob/dev/CONTRIBUTING.md?plain=1#L120

The base branch was changed.