Startup error handling

Proper error handling during the startup for the non-recoverable states.

For example:
If we fail to sign request because of missing credentials, terminate the controller instead of retrying
```
failed to sign request: failed to retrieve credentials: no EC2 IMDS role found
```

The issue names no files, tests, or entry points. Trace the controller's startup path and request-signing failure handling, then verify the missing-credentials example terminates the controller instead of being retried while recoverable startup failures retain their existing behavior.

Written by the indexing model from the issue text.