Android: Adding same gallery photo twice to a feature shares sketches; only one file remains after sync

Description
When the same image is attached twice to the same point feature from the device gallery, and a separate photo sketch is drawn on each, the app treats both attachments as the same underlying photo:

• Photo sketch annotations are effectively shared / copied between them (second sketch overwrites or merges).
• After synchronization, only a single photo file is present in the project on the server (second attachment not preserved as a distinct file).
  This causes data loss (loss of the second annotated variant) and misleading UI (appears like two attachments locally before sync).

Environment
staging

Application (+ app version, build, operating system)

• Mergin Maps Mobile (Android)
• App version: 2025.6.0 (714011)
• Device: Samsung Galaxy Tab Active5, Android 14
• Test project: tester-ws-1/test_photo-sketches

Steps to reproduce

1. Open project tester-ws-1/test_photo-sketches on Android.
2. Add a point feature in layer "point_photo2_layer".
3. Add a photo from device gallery (Photo A).
4. Add a second attachment to the same feature by selecting the SAME gallery image (Photo A again).
5. Add photo sketches to both photos
6. Observe both attachments locally (they appear as two).
7. Sync the project.
8. Check record in QGIS -> only one picture with both sketches was added to the project folder.

Actual results

• The two attachments are not truly independent: the photo sketch from one appears on (or overwrites) the other.
• After sync, only one physical photo file is stored on the server (second instance not duplicated).
• The second distinct sketch (annotation changes) is lost or merged—cannot retrieve both annotated variants.

Expected results

• Each time a user attaches a photo—even if sourced from the same gallery image—it should be treated as a distinct attachment instance with its own:
  • Stored file (unique filename)
  • Independent sketch layer / annotation data
• Sync should preserve both annotated variants separately (e.g. photoA.jpg and photoA_2.jpg or hashed unique names).
• No cross‑contamination of sketches between distinct attachments.
• UI should reflect any deduplication (if intended) explicitly; otherwise avoid silent de-duplication.

Screenshots or logs
Mobile app:

https://github.com/user-attachments/assets/442d5a88-d3b2-4e7e-82cb-7df53d5bc483

QGIS:

Conclusion
Created by GitHub Copilot and supervised by a human test analyst.

No source file or test is named in the report. Start by reproducing the issue in tester-ws-1/test_photo-sketches on Android, then trace how repeated gallery attachments, photo sketches, and synchronization are handled. Done means both attachments retain independent sketches and remain as separate files after sync.