guard prefix and wine edits while their apps run

development.md

@@ -14,7 +14,8 @@ src/               main process (Node/Electron backend)
     games.js       games service: run/stop state, wine resolution, open-with handoff
     lansync.js     LAN sync handlers (identity, devices, re-roll, sync + progress)
   runner.js        spawns wine/proton (env, prefix, playtime, logs)
-  library.js       apps registry (apps.json) + settings + playtime files
+  library.js       apps registry (apps.json) + settings + playtime files, plus
+                   the "which prefix does this app use" / in-use guards
   wines.js         wine/proton build scan, registry, portable symlink healing
   prefixes.js      prefix registry (files/wineprefixes)
   symlinks.js      relative symlink rewiring + executable-bit restoration
@@ -37,7 +38,8 @@ renderer/          UI (plain HTML/CSS/JS, no framework)
   style.css        the whole look; CSS variables at the top
 files/             portable data the launcher ships/creates at runtime
   translations/    en-us.json, pl.json (copied to the data dir on start)
-test/              plain node scripts, run them with `node test/<name>.test.js`
+test/              plain node scripts, run them with `node test/<name>.test.js`;
+                   electron test/<name>.test.js for ones that need the real IPC/Electron
 tools/             install.sh / createshortcut.sh / build helpers
 ```
 
@@ -66,6 +68,11 @@ handlers in src/ipc/. Keep new APIs in that pattern.
   try/catch-and-ignore with a comment saying why it is safe to ignore.
 - Windows apps run through runGame()/buildEnv() - never spawn wine directly
   somewhere else (prefix handling, Proton env and playtime live there).
+- A prefix or wine build that a running app uses cannot be renamed/deleted
+  (wine holds its registry and user files open in that folder): the guards sit
+  next to the handlers in src/ipc/, use the games service's running list plus
+  the helpers in library.js (prefixNameForGame/gamesUsingPrefix/is*InUse) and
+  answer { ok:false, error:'inUse'|'hasApps', apps:[names] } for the toast.
 - CSS: reuse the existing variables/classes (.button, .field-label,
   .custom-select, form-card); spacing rhythm comes from --button-margin and
   the flex gap of the container, not per-element magic numbers.