fix(config-backup): probe a custom folder before the retention fallback reads it, test that Save omits a displayed-only retention

docs/wiki/Config-Backups.md

@@ -139,9 +139,9 @@ Only the tracked names are ever written, whatever a manifest lists.
 
 Restoring `settings.json` keeps the four backup settings (on or off, folder, how many, how many
 days) at their current values, so a restore from before a folder change does not point the list
-at the old folder and hide the `pre-restore` copy it just made. The exception is a live
-`settings.json` that has none of the four (a reset file): the restore then keeps the backup's own
-how-many and how-many-days, so the next pass does not fall back to 20 copies and 30 days. The
+at the old folder and hide the `pre-restore` copy it just made. The exception is the two
+retention values: where the live `settings.json` lacks one (a reset file), the restore keeps the
+backup's own, key by key, so the next pass does not fall back to 20 copies and 30 days. The
 `pre-restore` copy records the retention in force too.
 
 Settings are re-read on the next request, so reload the page. `.env` and `push-keys.json` are

docs/wiki/Settings-Reference.md

@@ -193,7 +193,8 @@ mode, the **Users** administration entry is injected here.
 The **Config backups** group controls timestamped copies of your configuration files: an
 on/off switch (on by default), the backup folder (default `~/.codeman/backups/config`), how
 many backups to keep (2 to 500, default 20) and how many days to keep them (0 to 3650, default
-30; 0 means no age limit), plus **Back up now** and a list with **Restore**. These are
+30; 0 means no age limit). A value that is not saved in `settings.json` (a reset file) is whatever
+the newest backup in that folder recorded, and the default only when none did, plus **Back up now** and a list with **Restore**. These are
 server-side settings, read fresh. Details, naming and restore behaviour are on
 [Config Backups](Config-Backups).
 

docs/wiki/Troubleshooting.md

@@ -147,6 +147,10 @@ it again and save before looking for the list; until then the list shows the def
 After a reinstall of the data directory the old backups are unlisted because the instance has a
 new id; see [Config Backups](Config-Backups) for how to make them visible again.
 
+A backup is never dated earlier than the newest one, so if the clock was once set to a far
+future date, every later backup keeps that date. Delete the future-dated backup folder to
+return to normal dating.
+
 Without the UI: the backups are plain folders in `~/.codeman/backups/config/`
 (`cfg-YYYYMMDD-HHMMSS`); copy the file you need back over the one in `~/.codeman/`.