## Summary
This PR adds packet path validation before key construction and
presigning. Invalid paths are rejected before reaching either
object-store client implementation, ensuring consistent behavior
regardless of the underlying storage configuration.
This allows seamless migration to different object storage.
Existing runs that have offloaded payloads/outputs will continue to use
the default object store (configured using `OBJECT_STORE_*` env vars).
You can add additional stores by setting new env vars:
- `OBJECT_STORE_DEFAULT_PROTOCOL` this determines where new run large
payloads will get stored.
- If you set that you need to set new env vars for that protocol.
Example:
```
OBJECT_STORE_DEFAULT_PROTOCOL=“s3"
OBJECT_STORE_S3_BASE_URL=https://s3.us-east-1.amazonaws.com
OBJECT_STORE_S3_ACCESS_KEY_ID=<val>
OBJECT_STORE_S3_SECRET_ACCESS_KEY=<val>
OBJECT_STORE_S3_REGION=us-east-1
OBJECT_STORE_S3_SERVICE=s3
```
---------
Co-authored-by: nicktrn <55853254+nicktrn@users.noreply.github.com>