ds002785: minimal babs init fails — PermissionError stat-ing embedded FreeSurfer derivatives (likely transient)

**TL;DR:** Not sure what happened — minimal `babs init` died with a `PermissionError` stat-ing a file in this dataset's embedded FreeSurfer derivatives, but **anat passed on the same data**. Likely a transient dartfs NFSv4-ACL flake. **TODO: re-run minimal before digging in any further** — if it passes, close this.

## What happened
During `babs init` of the minimal project, babs runs a recursive `datalad drop` that `os.stat`s every file in the analysis dataset — including the embedded `sourcedata/raw/derivatives/freesurfer/` tree — and failed:

```
PermissionError: [Errno 13] Permission denied:
.../sourcedata/raw/derivatives/freesurfer/sub-0197/surf/rh.sphere.reg
```

(`bootstrap.py` → `datalad drop` → `status` → `diffstatus` → `os.stat`)

## Why it looks transient, not a dataset fault
- The file is a normal git-annex symlink, owned by us with owner `rwx`, pointing at a present-looking annex object — not a missing object (that would be `ENOENT`, not `EACCES`).
- **anat passed on the same dataset**: its `babs init` ran the same recursive drop/stat over the same embedded derivatives without error.
- Fits the `Failed to instantiate ACL` / `An error occurred during recursive file tree walk` dartfs NFSv4-ACL noise seen across many jobs (including passing ones).

## Notable dataset property
ds002785's raw dataset ships an embedded `derivatives/freesurfer/` tree (bloats every clone; gives the ACL flake more surface to hit).

## Done when
- [ ] Re-run minimal for ds002785.
- passes → close (was transient).
- fails again at the same `os.stat` → reproducible dartfs-ACL / git-annex interaction; investigate ACLs then.

Start by rerunning minimal babs init for ds002785, as requested in the issue. If it passes, the task is complete and the issue can be closed; if it fails again at os.stat on the listed FreeSurfer path, begin with bootstrap.py and the datalad drop/status/diffstatus call chain, then investigate the reported dartfs ACL interaction.

Written by the indexing model from the issue text.