**Related issue:** Resolves#42754
# Checklist for submitter
If some of the following don't apply, delete the relevant line.
- [x] Changes file added for user-visible changes in `changes/`,
`orbit/changes/` or `ee/fleetd-chrome/changes`.
See [Changes
files](https://github.com/fleetdm/fleet/blob/main/docs/Contributing/guides/committing-changes.md#changes-files)
for more information.
- [x] Input data is properly validated, `SELECT *` is avoided, SQL
injection is prevented (using placeholders for values in statements), JS
inline code is prevented especially for url redirects, and untrusted
data interpolated into shell scripts/commands is validated against shell
metacharacters.
## Testing
- [x] Added/updated automated tests
- [x] QA'd all new/changed functionality manually
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
* **Bug Fixes**
* Improved app manifest retrieval with automatic fallback to hosted
copies when the primary source is unavailable, reducing sync failures.
* **Documentation**
* Clarified that Fleet will fall back to hosted manifest copies if the
new manifest site is inaccessible.
* **New Features**
* Streamlined maintained-app synchronization to use a simpler sync
entrypoint and unified primary/fallback fetch logic.
* **Tests**
* Added comprehensive tests for primary/fallback fetch flows, error
handling, large-response truncation, and environment-based overrides.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
