[TEST] selective sync

README.md

@@ -77,11 +77,17 @@ Two PLWL installs on one LAN can mirror each other (sidebar → **LAN syncing**)
 
 - **Device ID** (24 chars) and **Sync code** (8 chars, letters+digits, case-insensitive), both re-rollable. A caller must prove it knows its own code; each verification costs 2 s and one may run at a time, so guessing is pointless. A correct code still opens an **Accept/Decline popup** on the receiver (60 s timeout); declining or ignoring never touches this machine and keeps the pairing.
 - **Devices on your network** are found over UDP and visible only while PLWL runs there (a few seconds after it closes they are gone).
-- Pick what to push: **portable apps**, **prefix-imported apps**, **Wine/Proton builds**, **prefixes**, **Sync settings**. Only what is ticked travels — without **Sync settings** the other machine's defaults and app configs are untouched. An accepted code is stored with the device ID, so later syncs need no typing; a re-rolled code is forgotten and asked for again.
+- Pick what to push: **portable apps**, **prefix-imported apps**, **Wine/Proton builds**, **prefixes**, **Sync settings**. Each category also has a **Select** list: everything starts ticked, and unchecking an app, a build or a prefix keeps that item on both machines untouched. Only what is ticked travels — without **Sync settings** the other machine's defaults and app configs are untouched. An accepted code is stored with the device ID, so later syncs need no typing; a re-rolled code is forgotten and asked for again.
+
+  A prefix-imported app's own folder lives inside its prefix, not in `files/apps/`. Unchecking such an app leaves that folder alone even when the prefix itself is synced: the sender takes it out of the prefix unit and marks it as off-limits for deletion. The picker says so when the app is ticked but its prefix is not — the folder then stays behind with the prefix.
 
 **Both machines show a progress popup** (phase, unit, files, per-category counters like `Apps: 2/5`, transferred vs. planned bytes; the bar follows the current phase). The popups cannot be dismissed, and a sender hashing a big unit shows *Waiting for the other device…* instead of a dead popup — the sender pings while it works. They close on completion, or after 15 minutes of silence (and reopen if the sync turns out to be alive).
 
-The **sender is the source of truth**: differing files are overwritten, missing ones written, extras inside the synced trees (`files/apps/`, `files/wines/`, `files/wineprefixes/`, `files/data/icons/`) deleted. A tree the sender could not fully read is the exception: that unit is still written, but nothing on the other side is deleted for it, because a missing entry may only mean it was unreadable. Only one sync runs at a time (a second attempt on the same machine answers *busy*), and a transfer cut off mid-file leaves no half-written file behind. Files are compared with BLAKE2b-512 (SHA-512/SHA-256 fallback); **Force sync all files** skips the comparison. Hashes are cached per file (size + mtime), so an unchanged library costs nothing to re-sync. Permissions travel with the files, and symlinks are sent as **relative** paths whenever the target belongs to the launcher (a Proton prefix's links into its build keep working on the other machine); `dosdevices` and targets outside `files/` stay absolute, and links wine itself rewrote to absolute are relativized again on the wire, on import and before every run.
+The **sender is the source of truth for what it sends**: differing files are overwritten, missing ones written, and extras inside the synced trees (`files/apps/`, `files/wines/`, `files/wineprefixes/`, `files/data/icons/`) are removed — but only after the receiver says so. Nothing is deleted while the bytes move: each unit only *plans* its leftovers, and the receiver gets one popup at the end with the top-most folders that would go (a fully redundant folder is a single collapsed row, a partly redundant one can be expanded). Every row is ticked to delete; unchecking a folder or a file keeps it. **Keep everything** is always one click away, an unanswered or expired list removes nothing, and a tree the sender could not fully read is never pruned at all, because a missing entry may only mean it was unreadable.
+
+That review is the only deletion path, so no backup copy is ever made — the files simply stay on disk until the answer. Two things it cannot undo: files that exist on both sides with different content are **overwritten** with the sender's version (the popup says so; if a game is installed on both computers, leave its prefix out of the sync), and a file kept in one sync is proposed again the next time, since the mirror is recomputed from scratch every run.
+
+Only one sync runs at a time (a second attempt on the same machine answers *busy*), and a transfer cut off mid-file leaves no half-written file behind. Files are compared with BLAKE2b-512 (SHA-512/SHA-256 fallback); **Force sync all files** skips the comparison. Hashes are cached per file (size + mtime), so an unchanged library costs nothing to re-sync. Permissions travel with the files, and symlinks are sent as **relative** paths whenever the target belongs to the launcher (a Proton prefix's links into its build keep working on the other machine); `dosdevices` and targets outside `files/` stay absolute, and links wine itself rewrote to absolute are relativized again on the wire, on import and before every run. A peer that predates the review cannot sync units at all (it would prune without asking); update both machines.
 
 A sync also carries **how apps are set up**: wine build and prefix, args, env, DLL overrides, a native Linux app's isolation level and Force X11, playtime and last played. **Sync settings** carries the registry-level part even when no files move: default wine/prefix, custom build names, prefix registry, every app's configuration and the library order. It only patches what already exists (unknown ids are ignored, unknown apps/prefixes stay), deletes nothing, and playtime only grows — the higher counter wins. Language, window settings, logs and external (leave) apps stay local.