diff --git a/deploy/installer/Lea.iss b/deploy/installer/Lea.iss
index a2ab2d63d..e6625df4b 100644
--- a/deploy/installer/Lea.iss
+++ b/deploy/installer/Lea.iss
@@ -587,12 +587,16 @@ end;
 // --------------------------------------------------------------------
 function PrepareToInstall(var NeedsRestart: Boolean): String;
 var
-  LockPath: string;
+  AppDir, LockPath, BackupDir, SessionsDir: string;
   Lines: TArrayOfString;
   ResultCode: Integer;
 begin
   Result := '';
-  LockPath := ExpandConstant('{app}\lea_agent.lock');
+  AppDir := ExpandConstant('{app}');
+
+  // 1) Tuer une Lea en cours (via le PID du lock) pour liberer les DLL
+  //    python-embed. Ne tue QUE ce PID, jamais tous les pythonw du poste.
+  LockPath := AppDir + '\lea_agent.lock';
   if FileExists(LockPath) then
   begin
     if LoadStringsFromFile(LockPath, Lines) and (GetArrayLength(Lines) > 0) then
@@ -600,6 +604,27 @@ begin
     DeleteFile(LockPath);
     Sleep(1500);
   end;
+
+  // UPGRADE uniquement (install existante detectee via config.txt).
+  if FileExists(AppDir + '\config.txt') then
+  begin
+    // 2) BACKUP (rollback) : copie code+config vers <app>_backup, HORS
+    //    python-embed / sessions / logs (leger, rapide). Filet si la nouvelle
+    //    version deconne : Julien restaure ce dossier.
+    BackupDir := AppDir + '_backup';
+    Exec(ExpandConstant('{cmd}'),
+      '/c rmdir /s /q "' + BackupDir + '" 2>nul & robocopy "' + AppDir + '" "' + BackupDir +
+      '" /E /XD python-embed sessions logs __pycache__ /XF *.pyc /R:1 /W:1 /NFL /NDL /NJH /NJS /NP >nul 2>&1',
+      '', SW_HIDE, ewWaitUntilTerminated, ResultCode);
+
+    // 3) PURGE des captures accumulees (donnees d'apprentissage internes, non
+    //    exploitables cote clinique) : libere le disque. Le fix capture JPEG
+    //    evite que la saturation reprenne. Les logs (compliance 180j) restent.
+    SessionsDir := AppDir + '\agent_v1\sessions';
+    if DirExists(SessionsDir) then
+      Exec(ExpandConstant('{cmd}'),
+        '/c rmdir /s /q "' + SessionsDir + '"', '', SW_HIDE, ewWaitUntilTerminated, ResultCode);
+  end;
 end;
 
 // --------------------------------------------------------------------