Panic in buildDownloads when Files slice is empty (index out of range [0])

[devmapal]

Summary

Grout panics when opening the download flow for a game whose cached row has HasMultipleFiles == false and len(Files) == 0. The single-file branch in buildDownloads does g.Files[0] without a length check.

Environment

• Grout: v4.8.1.1-beta.6 (arm64, ROCKNIX on RK3566 / Anbernic RG DS)
• RomM server: 4.8.1
• CFW: ROCKNIX (nightly 20260429)

Steps to reproduce

1. Have a game in the local SQLite cache whose games.data_json omits a files array (observed after incremental cache updates).
2. Open game details and start download (or reach the download UI) for that title.
3. Process exits immediately with a Go panic.

Example

Game: Professor Layton and the Curious Village (Nintendo DS), games.id = 60 in grout.db. Cached data_json includes fs_name, full_path, metadata, etc., but no files key; instr(data_json, 'files') is 0.

Stack trace (excerpt)

panic: runtime error: index out of range [0] with length 0
	panic: sync: negative WaitGroup counter   // secondary, during SDL/gabagool cleanup after first panic

grout/ui.(*DownloadScreen).buildDownloads(...)
	/build/ui/download.go:372 +0x2288
grout/ui.(*DownloadScreen).draw(...)
	/build/ui/download.go:98
grout/ui.(*DownloadScreen).Execute(...)
	/build/ui/download.go:63

Last log line before panic: Using cached artwork for game details for the Layton title.

Expected behavior

No panic: either refuse download with a clear error (“no file metadata; refresh library”), or synthesize a download from fs_name / refetch full ROM from the API when Files is empty.

Suggested fix

In buildDownloads (ui/download.go), guard the non–HasMultipleFiles branch: if len(g.Files) == 0, return a handled error or build the download URL from existing fields (e.g. fs_name) after confirming RomM API contract.

Logs

• Application JSON log: Grout/logs/app.log
• Full panic on ROCKNIX also appeared in /var/log/exec.log (port launch stderr).

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This bug report was drafted with Cursor (AI-assisted investigation); facts and traces were verified on device.

[devmapal]

Update: In RomM the game entry had no ROM files attached in the UI. A full library rescan re-linked the files; Grout then saw file metadata again and downloads worked. A client-side guard for empty Files would still help for incomplete API/cache rows.

[pawndev]

Thanks for the report and the investigation! You're right, we will look at the code for guarding against a panic