fix: derive install paths from RomM folder (fs_name) for folder-based ROMs

[gantoine]

Fixes #124.

Problem

The install folder and ROM path were derived from the downloaded file name rather than from RomM's actual on-disk structure (fs_name), so paths didn't match the real files. This broke IsInstalled detection and the emulator play path — most visibly when a mapping points at a mounted RomM library.

• Nested single file (e.g. All-Star Baseball '99/All-Star Baseball '99 (Europe).zip): the folder was built from the file name → All-Star Baseball '99 (Europe) instead of the RomM folder All-Star Baseball '99.
• Multiple files (e.g. 1080 TenEighty Snowboarding/…): the folder was right, but the ROM path pointed at a nonexistent extensionless file …\1080 TenEighty Snowboarding instead of a real file inside the folder.

Fix

Thread the ROM's real folder (fs_name) through the path computation so paths mirror RomM's layout:

• RomMRevision / GameInstallInfo — add FolderName (fs_name for folder-based ROMs; null for simple single files, persisted in the sidecar).
• RomMRevisionFactory — set FolderName from fs_name for has_nested_single_file and multi-file ROMs.
• RomMInstallPaths — folder-aware InstallDir/GamePath overloads that pin the directory to <root>/<fs_name> when a folder name is present, falling back to the old file-name-derived behavior otherwise.
• RomMImport — install dir/path use FolderName; for multi-file ROMs the ROM path points at the primary real file (SelectPrimaryFile) instead of the folder placeholder.
• RomMInstallController / RomM.cs — install/download and sidecar-restore use the same folder-aware computation, keeping import-time and install-time paths in lockstep.

Simple single files are intentionally untouched, so already-downloaded games in the common case don't flip to "not installed".

Resulting paths now match disk exactly, e.g. Z:\roms\n64\All-Star Baseball '99\All-Star Baseball '99 (Europe).zip.

Tests

• RomMInstallPathsTests — folder-aware overloads + null/empty fallback.
• RomMRevisionFactoryTests — FolderName for simple-single / nested-single / multi-file.

Existing tests still pass (the 2-arg overloads remain). Not built locally (this is a .NET Framework project with no dotnet/msbuild on macOS); the Tests CI workflow links these pure-logic files and will run the suite.

🤖 Generated with Claude Code

[greptile-apps]

Greptile Summary

This PR aligns folder-based ROM paths with RomM's filesystem layout. The main changes are:

• Persists fs_name as revision and install metadata.
• Uses folder-aware paths during import and installation.
• Selects a real file as the play path for multi-file ROMs.
• Adds tests for folder assignment and path fallback.

Confidence Score: 4/5

Multi-file imports can still produce nonexistent play paths, and remote folder names can escape the configured install root.

• Empty file metadata falls back to an extensionless placeholder.
• Nested primary files lose their relative directory.
• Rooted folder values can redirect filesystem writes.

Games/RomMImport.cs and Games/RomMInstallPaths.cs

Security Review

The new folder-aware path accepts the remote fs_name without checking that the normalized destination remains under the configured install root. A rooted value can redirect downloads and extraction outside that root.

Important Files Changed

Filename	Overview
Games/RomMImport.cs	Adds folder-aware import paths, but multi-file paths can still point to nonexistent files when metadata is empty or nested.
Games/RomMInstallController.cs	Uses the persisted folder name for the download and extraction directory.
Games/RomMInstallPaths.cs	Adds folder-aware path helpers without validating that the remote folder remains under the install root.
Games/RomMRevisionFactory.cs	Assigns folder metadata for nested single-file and multi-file ROMs while preserving simple-file behavior.
Models/RomM/Rom/GameInstallInfo.cs	Carries the folder name into the installation workflow.
Models/RomM/Rom/RomMRomLocal.cs	Persists folder metadata in local revision sidecars.
RomM.cs	Propagates folder metadata for default and user-selected revisions.
RomM.Tests/RomMInstallPathsTests.cs	Covers normal folder pinning and null or empty fallback behavior.
RomM.Tests/RomMRevisionFactoryTests.cs	Covers folder metadata for simple, nested, and multi-file ROM shapes.

Prompt To Fix All With AI

Fix the following 3 code review issues. Work through them one at a time, proposing concise fixes.

---

### Issue 1 of 3
Games/RomMImport.cs:199-202
**Empty File List Restores Placeholder Path**

When a multi-file ROM has no populated `Files` entries, `SelectPrimaryFile` returns null and this falls back to the extensionless display name in `ROM.Name`. The resulting path does not match any extracted file, so `IsInstalled` remains false and the imported play path cannot launch the game.

### Issue 2 of 3
Games/RomMImport.cs:199-204
**Primary File Loses Relative Path**

When the selected file is below another directory in a multi-file ROM, using only `FileName` constructs `<installDir>/<fileName>` while extraction preserves the nested path. `File.Exists` then checks a nonexistent file and the imported emulator path is invalid.

### Issue 3 of 3
Games/RomMInstallPaths.cs:21-24
**Rooted Folder Escapes Install Root**

`folderName` comes from RomM's `fs_name` and is passed directly to `Path.Combine`. If a malformed or compromised server returns a rooted path, `Path.Combine` discards `rootInstallDir`, allowing the download and archive extraction to write outside the configured mapping.

_{Reviews (1): Last reviewed commit: "fix: derive install paths from RomM fold..." | Re-trigger Greptile}