fix: migration method selection navigation bug (W-23306091)

[sbosio]

Summary

The issue was caused because selectedMigrationMethod was overloaded as both the data value (POST body) and the control gate deciding whether to show the method prompt. Once set —interactively or via flag— it stayed truthy, so the prompt was skipped on the next pass (after "Go back", or for a second migration in the same session).

The fix was to introduce a new attribute to record if the method was provided via flag and ensure the selectedMigrationMethod gets reset each time a new migration is configured.

Added one unit test that selects one of the methods and then goes back to select the other one and verifies the POST is done with the correct method (the last one selected) and that the prompt appears two times as expected.

Type of Change

Patch Updates (patch semver update)

• fix: Bug fix

Testing

Notes:
You'll need to have at least a classic Postgres database on your app (and recommended, optionally an available and empty Advanced one).

Steps:

1. Checkout this branch and run

   npm install && npm run build

2. Run

   heroku data:pg:migrate --app example-app

   Follow the interactive steps to configure a migration from the classic DB to the Advanced one with any migration method. On the confirmation step select Go back and observe you're redirected to the destination database selection step instead of the migration method selection and you cannot change the migration method. Cancel the migration configuration with CTRL+C.
3. Repeat the test with the fixed command

   ./bin/run data:pg:migrate --app example-app

   Verify that now you're allowed to go back to the migration method selection step and change the migration method before confirmation.

Screenshots (if applicable)

Related Issues

GUS work item: W-23306091