Handle image import setup failures

[yusufhay]

What?

Adds explicit error handling for image import setup failures.

Why?

The image import ability writes generated image data to a temporary file and then sideloads it into the media library. If WordPress cannot create the temporary file, or if the image MIME type cannot be mapped to a file extension, the ability should return a clear WP_Error instead of continuing with invalid file state.

How?

Checks the result of wp_tempnam() before writing image data. Also checks the file extension returned by wp_get_default_extension_for_mime_type() and deletes the temporary file before returning an error when the MIME type cannot be mapped.

Use of AI Tools

AI assistance: Yes
Tool(s): Codex / ChatGPT
Model(s): GPT-5
Used for: Reviewing the image import control flow for unhandled failure paths and drafting the minimal guards. I reviewed the change and PR description before submitting.

Testing Instructions

1. Install and activate this PR build of the AI plugin.
2. Enable image generation and connect a provider that supports image generation.
3. Generate an image and import it into the media library.
4. Confirm the image is imported successfully and its media fields are preserved as before.
5. To validate the failure handling, simulate an unmapped image MIME type when calling the image import ability and confirm it returns a WP_Error instead of attempting to sideload a file with an invalid extension.

Screenshots or screencast

Not applicable. This PR does not change the UI.

Changelog Entry

Fixed - Return clear errors when generated image import setup fails.

[github-actions]

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Co-authored-by: yusufhay <[email protected]>

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.61%. Comparing base (64e8032) to head (d078baa).

Additional details and impacted files

@@              Coverage Diff              @@
##             develop     #657      +/-   ##
=============================================
+ Coverage      74.57%   74.61%   +0.04%     
- Complexity      1754     1758       +4     
=============================================
  Files             85       85              
  Lines           7548     7561      +13     
=============================================
+ Hits            5629     5642      +13     
  Misses          1919     1919              

Flag	Coverage Δ
unit	74.61% <100.00%> (+0.04%)	⬆️

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[dkotter]

While I'm all for hardening existing code, I'm trying to understand in what situations these scenarios will happen. Reading the PR description doesn't give me a good idea of what scenarios these problems will occur or how to go about reproducing the problems myself.