25.08 (x86_64): flatpak pull fails with HTTP 404 since Aug 21 publish — content objects missing from CDN

### Summary

Since the `Update rust and rust-analyzer modules` build published on **2026-08-21 01:50 UTC** (manifest commit `7c4a7fdd750d`), installing `runtime/org.freedesktop.Sdk.Extension.rust-stable/x86_64/25.08` from Flathub fails with `Server returned HTTP 404`.

The ref/binding metadata was updated, but the actual content objects appear to be missing from the repo/CDN — i.e. the publish looks incomplete.

### Evidence

From a GitHub Actions runner (`flatpak install --user flathub org.freedesktop.Sdk.Extension.rust-stable//25.08`) with `--ostree-verbose`:

```
F: flatpak_dir_pull: Using commit 4d0c0a79... for pull of ref runtime/org.freedesktop.Sdk.Extension.rust-stable/x86_64/25.08
F: queuing fetch of ef6e15f3...file
F: queuing fetch of d6d4053f...file
...
Error: While pulling runtime/org.freedesktop.Sdk.Extension.rust-stable/x86_64/25.08 from remote flathub: Server returned HTTP 404
```

So the binding commit resolves fine, but the `.file` content objects it references return 404.

In the same environment, `org.freedesktop.Platform`, `org.freedesktop.Sdk` and `org.freedesktop.Sdk.Extension.node22` all install successfully — only `rust-stable` is affected.

The ref has since moved from `4d0c0a79…` to a newer binding commit `64621c8b…` (xa.from_commit `5c0050f5…`), but it is still broken: as of **2026-08-24 04:01 UTC**, 6 consecutive install attempts over ~11 minutes all failed with HTTP 404 ([example CI run](https://github.com/ponponon/aivplayer/actions/runs/32687696454)).

### Impact

Any downstream project whose Flatpak manifest declares `sdk-extensions: [org.freedesktop.Sdk.Extension.rust-stable]` cannot build/install right now.

### Question

Could the 25.08 build be re-published so the content objects are fully uploaded? Happy to provide more details if needed.

Start by reproducing the install with `flatpak install --user flathub org.freedesktop.Sdk.Extension.rust-stable//25.08` and `--ostree-verbose`, checking the binding commits 4d0c0a79… and 64621c8b… plus their referenced content objects. Compare the affected rust-stable ref with the working platform and node22 refs. Done means the 25.08 x86_64 ref and all referenced `.file` objects are available and installation completes without HTTP 404.

Written by the indexing model from the issue text.