## Why
Configured Git marketplaces may be defined outside the user config, but those definitions could not download or update their snapshots.
## What changed
- Select marketplace source, ref, and sparse-path settings from the effective merged configuration for startup synchronization and explicit upgrades.
- Preserve the initiating operation's configuration loader and overrides when reloading before activation.
- Roll back activation if the marketplace definition changed or configuration can no longer be loaded, without copying settings into the user config.
## Testing
- Cover system-defined marketplaces, CLI overrides, startup fallback after invalid user configuration, and rollback after configuration changes.
GitOrigin-RevId: 53d1eecf68a91ce2aa8430e5749d78697bfcd821
