[Mr-Milk]

Summary

WSIData.write() without a file_path raised only when both the store and the path were unset, but then always wrote to the store. A WSIData opened from a SpatialData, with open_wsi(sdata, image_key=...), takes the path of that SpatialData in from_spatialdata() and never gets a store. So write() passed None on to SpatialData.write and failed with ValueError: file_path must be a string or a Path object, type(file_path) = <class 'NoneType'>. So did a second write() after open_wsi(..., store=None) and write(file_path).

• write() now falls back to the path when there is no store. The store still comes first when both are set.
• A SpatialData written from memory keeps its elements in memory, and the WSIData is written back to its path.
• A SpatialData read from disk loads its images, labels and points lazily from that path. Since fix: refuse to overwrite a store that lazily loaded elements read from #85, write() refuses to overwrite such a path, so here it raises fix: refuse to overwrite a store that lazily loaded elements read from #85's Cannot overwrite … ValueError instead of the misleading one, and the store is left intact. Without fix: refuse to overwrite a store that lazily loaded elements read from #85, the fallback would have deleted the store and then read the deleted files back.

Tests

• test_write_without_store_goes_to_path: a SpatialData written from memory is opened with open_wsi(sdata, image_key=...), and write() saves the added tissues into its path. Before the fix: ValueError: file_path must be a string or a Path object, type(file_path) = <class 'NoneType'>.

Checked by hand, not as tests:

• open_wsi(read_zarr(p), image_key=...) then write() raises fix: refuse to overwrite a store that lazily loaded elements read from #85's error, and the image in p is unchanged.
• open_wsi(slide, store=None), write(x), then write() writes to x.

Verification

• Python 3.14: 137 passed, 14 skipped (readers and dependencies that are not installed).
• ruff check and format pass.

[Copilot]

Copilot review overview

🟢 Approval recommended

The fallback is correct, preserves existing precedence, and has focused regression coverage.

Review effort: Balanced
Findings: None

What changed in this PR

Fixes WSIData.write() to use its inherited SpatialData path when no WSI store is configured.

Changes:

• Adds path fallback while preserving store precedence.
• Adds regression coverage for writing SpatialData-backed instances.

File	Description
wsidata/​_model/​core.py	Falls back to self.path when _wsi_store is absent.
tests/​test_wsidata.py	Verifies writing added tissues to the fallback path.

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