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

src/web/public/settings-ui.js

@@ -1374,6 +1374,25 @@ Object.assign(CodemanApp.prototype, {
   // ── Config backups ──────────────────────────────────────────────────────────
   // Server-side files, so these read the SAVED settings: a folder or retention edit applies after Save.
 
+  /**
+   * The retention keys a Save sends: a value only once it was saved before or edited here. After a reset
+   * the form merely DISPLAYS what the passes use (the retention the backups recorded), and writing that back
+   * would replace it with whatever a different folder or an older default says.
+   */
+  _configBackupRetentionPayload(prev) {
+    const count = document.getElementById('appSettingsConfigBackupKeepCount');
+    const days = document.getElementById('appSettingsConfigBackupKeepDays');
+    const out = {};
+    if (prev.configBackupKeepCount !== undefined || count.dataset.touched) {
+      out.configBackupKeepCount = Math.min(500, Math.max(2, parseInt(count.value, 10) || 20));
+    }
+    if (prev.configBackupKeepDays !== undefined || days.dataset.touched) {
+      const n = parseInt(days.value, 10);
+      out.configBackupKeepDays = Math.min(3650, Math.max(0, Number.isNaN(n) ? 30 : n));
+    }
+    return out;
+  },
+
   /** Fill the backup list, and show the default folder as the input's placeholder. */
   async loadConfigBackups() {
     const out = this.$('configBackupList');
@@ -2887,14 +2906,7 @@ Object.assign(CodemanApp.prototype, {
       mcpSyncEnabled: document.getElementById('appSettingsMcpSync').checked,
       configBackupEnabled: document.getElementById('appSettingsConfigBackup').checked,
       configBackupDir: document.getElementById('appSettingsConfigBackupDir').value.trim(),
-      // Sent only once saved before or edited here: a value merely displayed from the server (after a reset)
-      // would otherwise be written back and replace the retention the backups recorded.
-      ...(_prev.configBackupKeepCount !== undefined || document.getElementById('appSettingsConfigBackupKeepCount').dataset.touched
-        ? { configBackupKeepCount: Math.min(500, Math.max(2, parseInt(document.getElementById('appSettingsConfigBackupKeepCount').value, 10) || 20)) }
-        : {}),
-      ...(_prev.configBackupKeepDays !== undefined || document.getElementById('appSettingsConfigBackupKeepDays').dataset.touched
-        ? { configBackupKeepDays: Math.min(3650, Math.max(0, Number.isNaN(parseInt(document.getElementById('appSettingsConfigBackupKeepDays').value, 10)) ? 30 : parseInt(document.getElementById('appSettingsConfigBackupKeepDays').value, 10))) }
-        : {}),
+      ...this._configBackupRetentionPayload(_prev),
       readMyMindEnabled: document.getElementById('appSettingsReadMyMind').checked,
       ultracodeFloatingWindows: document.getElementById('appSettingsUltracodeFloatingWindows').checked,
       showMultiMonitorButton: document.getElementById('appSettingsShowMultiMonitorButton').checked,