Install and update test cases, for the release that breaks existing users

A fresh install is the least representative test you can run, because almost nobody experiences the app that way after launch. The population that matters is people upgrading, and they arrive carrying local data written by an older schema, preferences under keys that may have been renamed, queued actions not yet synced, and a credential in whatever format the previous build stored. Every one of those is a migration, and migrations are only correct if they run in the right order from whatever version the user actually has. Testing one step at a time misses the user who skipped four releases, which is a large share of any real user base.

The crash during migration deserves its own case because it produces the worst possible outcome: an app that fails on every launch and cannot be recovered without reinstalling, which throws away the local data the migration was supposed to protect. The defence is not to migrate in place. Write the new state alongside the old, swap when complete, and keep the previous data readable until it succeeds. Low storage belongs in the same group, since a migration that runs out of disk halfway leaves exactly the same broken state.

Forced update is a control that regularly causes the outage it was meant to prevent. If the client blocks when the version check is unreachable, then any failure of that endpoint locks out every user at once, and the fix requires the endpoint you cannot reach. Failing open is the correct default. The mirror image is version tolerance on the server: users who never update are permanent, so an older client has to keep working against the current API, and the client has to parse an unknown field or an unrecognised enum value without crashing rather than treating anything unexpected as fatal.

Finally, the small things are what users actually report. Preferences that reset because a key was renamed read as the app forgetting them. A deep link followed before installing that lands on a generic home screen wastes the campaign that generated it. A permission revoked in system settings while the app is backgrounded will crash any code that assumes it still holds. And a reinstall has to genuinely start clean locally while restoring server side data and purchased entitlements, because an entitlement that does not come back is a refund request.