check_file_permissions: probe inside target store, not its parent (#1098)

[gaoflow]

Closes #1098.

Problem

check_file_permissions writes its probe file to the parent of the target directory instead of the target itself when given an FSMap (the zarr/cloud path). As reported in #1098, for a target of .../combined_files the probe was created at .../ :

File Directory Root :  .../notebooks/combined_files
Test file generated at :  .../notebooks/.f0605b17-...

This means the permission check validates the wrong directory, and (when parent and target permissions differ) can pass or fail incorrectly.

Cause

The FSMap branch used base_dir = os.path.dirname(FILE_DIR.root), which strips the last path component, so the probe lands one level up. The Path/str branch right below it correctly writes inside the target (and mkdir(parents=True) first).

os.path.dirname was presumably used because the target store may not exist yet (e.g. a not-yet-written zarr store), and writing inside a missing directory raises — but that's exactly the case the Path/str branch already handles by creating the directory first.

Fix

Write the probe inside FILE_DIR.root and makedirs(..., exist_ok=True) first, mirroring the Path/str branch. This keeps the check on the actual target and still works when the store doesn't exist yet (it gets created, as the local-path branch already does).

Tests

Added two regression tests (red before, green after):

• test_check_file_permissions_fsmap_writes_inside_target — the probe is opened inside the target store, not its parent.
• test_check_file_permissions_fsmap_creates_missing_store — a not-yet-created store is created and passes the check.

Full test_utils_io.py passes (47 passed, 2 xfailed).

[LOCEANlloydizard]

Hi @gaoflow, thanks! the fix and tests both look good to me! cheers!