fix: close mask image file handle in /upload/mask endpoint

[mango766]

Fixes #13335

What

In the /upload/mask handler, the uploaded mask image was opened without a context manager:

# before
mask_pil = Image.open(image.file).convert('RGBA')

Image.open() returns a lazy-loaded image that keeps the underlying file descriptor open. Calling .convert() produces a new in-memory copy but does not close the original. Without an explicit close the file handle leaks — it's only reclaimed when CPython's refcount drops to zero (i.e. next GC cycle), which is non-deterministic.

The original image a couple lines above was already using a context manager correctly; this PR brings the mask open in line with that pattern:

# after
with Image.open(image.file) as mask_pil_raw:
    mask_pil = mask_pil_raw.convert('RGBA')

Why it matters

Under sustained mask-upload load the leaked descriptors can push the process past the OS limit (ulimit -n, default 1024 on most Linux distros), causing "Too many open files" errors.

Change

• server.py: wrap Image.open(image.file) in a with block (1-line net change)

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Reviewing files that changed from the base of the PR and between 2d861fb and 4b97d16.

📒 Files selected for processing (1)

• server.py

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📝 Walkthrough

Walkthrough

The upload_mask function in server.py has been modified to change how the mask image is loaded. The image file opening now uses a context manager pattern to ensure proper resource cleanup. The PIL image is opened within a context manager, converted to RGBA format, and the file handle is closed after the conversion. The subsequent image manipulation logic remains unchanged.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the primary fix: closing a mask image file handle in the /upload/mask endpoint.
Description check	✅ Passed	The description is well-related to the changeset, explaining the issue, the fix, and why it matters with clear before/after code examples.
Linked Issues check	✅ Passed	The PR directly addresses issue #13335 by implementing the exact fix specified: wrapping Image.open(image.file) in a context manager to ensure proper file handle closure.
Out of Scope Changes check	✅ Passed	All changes are narrowly scoped to the specific file descriptor leak fix in the /upload/mask endpoint with no unrelated modifications.

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