File preview keeps a stale failure when revisiting a repaired media file

[jrusso1020]

The file preview remembers a failed media path after the user visits another file. Returning to the original file can display the old error without making a new request, even after the file becomes available.

Reproduction and evidence

Verified against origin/main 86fa10c on September 23, 2026. The relevant component and its caller are unchanged from the browser probe.

Keep one MediaPreview mounted and change its props as the file panel does:

1. Render project test, file broken.png; serve its preview URL with HTTP 404. The error panel appears.
2. Make broken.png available, then switch to healthy.png, served as a valid image. Its image loads successfully.
3. Switch back to broken.png. The old error appears immediately and no new image request is made.

A Chrome probe using the actual component and intercepted HTTP responses recorded only:

/api/projects/test/preview/broken.png
/api/projects/test/preview/healthy.png

The returned view still said Couldn't load this file — it may be missing or corrupt. Changing the project prop to second while retaining broken.png also retained the error without requesting the second project's image.

This is a browser component reproduction. StudioLeftPanels renders MediaPreview without a file key, which supports the same-file-panel switching path. A complete Studio navigation session has not been run; the cross-project symptom is only asserted for a retained component instance, not for shell navigation that remounts it.

Scope

Tie media failure state to the current preview lifecycle/source identity so visiting another file or changing projects does not carry a previous error into a fresh preview. Preserve useful errors for genuinely unavailable images, videos, and audio. Do not add background polling or automatic retry loops.

Acceptance criteria

• Failed image A → healthy image B → repaired A attempts to load A again and displays it successfully.
• Failed image A → binary file B → repaired A also retries A on returning.
• Changing project with the same file path does not inherit the old project's failure when the component remains mounted.
• A file that still fails continues to show the existing error panel without repeated automatic requests.
• Include focused component regression coverage and verify the file-switching flow in Studio before considering the issue resolved.

Code pointers and validation

• MediaPreview failure state
• File-panel caller
• Read packages/studio/AGENTS.md; run Studio tests with bun run --cwd packages/studio test.

Difficulty: easy — localized state identity and reset behavior with a small regression fixture. Before starting, check current assignments and linked PRs. Open UI migration PRs #3625, #3626, #3774 and #3776 contain only image/video border-radius class changes in this file. PR #4370's file-tree and missing-composition work does not change this component or its caller.

Reviewer/mentor is being arranged. Comment with your intended approach before starting so ownership can be coordinated; this issue is not yet a newcomer invitation.