diff --git a/client/src/pages/DsiOpex.tsx b/client/src/pages/DsiOpex.tsx
index c71efd9..227078b 100644
--- a/client/src/pages/DsiOpex.tsx
+++ b/client/src/pages/DsiOpex.tsx
@@ -493,6 +493,19 @@ export default function DsiOpex() {
 
   const CATEGORIES_FILTER = useMemo(() => ['Toutes', ...categoriesPresentes], [categoriesPresentes]);
 
+  // Basculer le mode de ventilation d'une ligne (Prorata classe 6 ↔ Manuel)
+  const handleToggleVentilation = useCallback((id: string) => {
+    if (isValidated) return;
+    setOpexState(prev => ({
+      ...prev,
+      lignes: prev.lignes.map(l => l.id === id ? {
+        ...l,
+        mode_ventilation: (l.mode_ventilation === 'Manuel') ? 'Prorata classe 6' : 'Manuel',
+      } : l),
+    }));
+    setIsDirty(true);
+  }, [isValidated]);
+
   // Modifier un montant directement dans le tableau
   const handleMontantChange = useCallback((id: string, value: number) => {
     if (isValidated) return;
@@ -683,14 +696,20 @@ export default function DsiOpex() {
       const montantsRecalcules: Record<string, number> = {};
       let totalEtab = 0;
       for (const ligne of opexState.lignes) {
+        // Priorité : mode_ventilation de la ligne (modifié par l'utilisateur) > source JSON > isCustom
         const srcPoste = srcData.postes.find(p => p.libelle === ligne.libelle);
-        const isManuel = srcPoste?.mode_ventilation === 'Manuel' || ligne.isCustom;
+        const modeVentilation = ligne.mode_ventilation ?? srcPoste?.mode_ventilation ?? null;
+        const isManuel = modeVentilation === 'Manuel' || ligne.isCustom;
         let montant: number;
         if (isManuel && etabOverrides[ligne.libelle] !== undefined) {
           // Override saisi manuellement par l'utilisateur
           montant = etabOverrides[ligne.libelle];
-        } else if (ligne.montant > 0) {
+        } else if (!isManuel && ligne.montant > 0) {
+          // Prorata automatique
           montant = Math.round(ligne.montant * ratio);
+        } else if (isManuel) {
+          // Manuel sans override : 0 (en attente de saisie)
+          montant = 0;
         } else {
           montant = 0;
         }
@@ -1122,7 +1141,28 @@ export default function DsiOpex() {
                             <td className="px-3 py-3 text-xs text-muted-foreground hidden lg:table-cell w-20 max-w-[80px] truncate" title={ligne.type || ''}>{ligne.type || '—'}</td>
                             <td className="px-4 py-3 text-sm text-muted-foreground hidden xl:table-cell">{ligne.facturation || '—'}</td>
                             {showDetails && <td className="px-4 py-3 text-xs font-mono text-muted-foreground hidden xl:table-cell">{ligne.compte || '—'}</td>}
-                            {showDetails && <td className="px-4 py-3 text-xs hidden xl:table-cell">{(() => { const mv = ligne.mode_ventilation || 'Prorata'; const isManuelV = mv === 'Manuel'; return <span className={`inline-flex px-2 py-0.5 rounded-full text-xs font-medium ${isManuelV ? 'bg-blue-100 text-blue-700' : 'bg-emerald-100 text-emerald-700'}`}>{mv}</span>; })()}</td>}
+                            {showDetails && (
+                              <td className="px-4 py-3 text-xs hidden xl:table-cell">
+                                {isValidated ? (
+                                  <span className={`inline-flex px-2 py-0.5 rounded-full text-xs font-medium ${
+                                    ligne.mode_ventilation === 'Manuel' ? 'bg-blue-100 text-blue-700' : 'bg-emerald-100 text-emerald-700'
+                                  }`}>{ligne.mode_ventilation || 'Prorata classe 6'}</span>
+                                ) : (
+                                  <button
+                                    onClick={() => handleToggleVentilation(ligne.id)}
+                                    title="Cliquer pour basculer Prorata ↔ Manuel"
+                                    className={`inline-flex items-center gap-1 px-2 py-0.5 rounded-full text-xs font-medium border transition-colors hover:opacity-80 cursor-pointer ${
+                                      ligne.mode_ventilation === 'Manuel'
+                                        ? 'bg-blue-100 text-blue-700 border-blue-300 hover:bg-blue-200'
+                                        : 'bg-emerald-100 text-emerald-700 border-emerald-300 hover:bg-emerald-200'
+                                    }`}
+                                  >
+                                    {ligne.mode_ventilation === 'Manuel' ? '🔒' : '🔓'}
+                                    {ligne.mode_ventilation || 'Prorata classe 6'}
+                                  </button>
+                                )}
+                              </td>
+                            )}
                             <td className="px-4 py-3 text-right text-sm text-muted-foreground tabular-nums">
                               {formatNum(ligne.budget_n1)}
                             </td>
@@ -1265,21 +1305,23 @@ export default function DsiOpex() {
 
               {/* Tableau scrollable horizontalement avec tous les postes */}
               <div className="bg-card border border-border rounded-xl overflow-hidden">
-                <div className="overflow-x-auto" style={{ isolation: 'isolate' }}>
+                <div className="overflow-x-auto overflow-y-auto" style={{ isolation: 'isolate', maxHeight: 'calc(100vh - 320px)' }}>
                   <table className="text-xs border-separate border-spacing-0" style={{ minWidth: 'max-content', width: '100%' }}>
                     <thead>
                       <tr className="border-b border-border bg-muted/40">
-                        <th className="text-left px-3 py-3 font-medium text-muted-foreground" style={{ position: 'sticky', left: 0, zIndex: 30, background: 'oklch(0.94 0.005 80)', boxShadow: '2px 0 4px -1px rgba(0,0,0,0.15)', width: '110px', minWidth: '110px', maxWidth: '110px' }}>Code</th>
-                        <th className="text-left px-3 py-3 font-medium text-muted-foreground" style={{ position: 'sticky', left: '110px', zIndex: 30, background: 'oklch(0.94 0.005 80)', boxShadow: '2px 0 8px -2px rgba(0,0,0,0.2)', width: '220px', minWidth: '220px', maxWidth: '220px' }}>
+                        <th className="text-left px-3 py-3 font-medium text-muted-foreground" style={{ position: 'sticky', left: 0, top: 0, zIndex: 40, background: 'oklch(0.94 0.005 80)', boxShadow: '2px 0 4px -1px rgba(0,0,0,0.15)', width: '110px', minWidth: '110px', maxWidth: '110px' }}>Code</th>
+                        <th className="text-left px-3 py-3 font-medium text-muted-foreground" style={{ position: 'sticky', left: '110px', top: 0, zIndex: 40, background: 'oklch(0.94 0.005 80)', boxShadow: '2px 0 8px -2px rgba(0,0,0,0.2)', width: '220px', minWidth: '220px', maxWidth: '220px' }}>
                           <SortBtn col="nom" label="Établissement" />
                         </th>
                         {/* Colonnes postes — vert = prorata auto, bleu = manuel */}
                         {opexState.lignes.map(ligne => {
                           const srcPoste = getOpexDataForAnnee(annee).postes.find(p => p.libelle === ligne.libelle);
-                          const isManuel = srcPoste?.mode_ventilation === 'Manuel' || ligne.isCustom;
+                          const modeVentilation = ligne.mode_ventilation ?? srcPoste?.mode_ventilation ?? null;
+                          const isManuel = modeVentilation === 'Manuel' || ligne.isCustom;
                           return (
                             <th
                               key={ligne.id}
+                              style={{ position: 'sticky', top: 0, zIndex: 35 }}
                               className={`text-right px-2 py-2 font-medium min-w-[90px] max-w-[110px] ${
                                 isManuel
                                   ? 'text-blue-700 bg-blue-50/60 border-b-2 border-blue-400'
@@ -1294,7 +1336,7 @@ export default function DsiOpex() {
                             </th>
                           );
                         })}
-                        <th className="text-right px-3 py-3 font-medium text-muted-foreground" style={{ position: 'sticky', right: 0, zIndex: 30, background: 'oklch(0.94 0.005 80)', boxShadow: '-2px 0 8px -2px rgba(0,0,0,0.2)', width: '120px', minWidth: '120px' }}>
+                        <th className="text-right px-3 py-3 font-medium text-muted-foreground" style={{ position: 'sticky', right: 0, top: 0, zIndex: 40, background: 'oklch(0.94 0.005 80)', boxShadow: '-2px 0 8px -2px rgba(0,0,0,0.2)', width: '120px', minWidth: '120px' }}>
                           <SortBtn col="total" label={`Total ${annee}`} />
                         </th>
                       </tr>
@@ -1308,7 +1350,8 @@ export default function DsiOpex() {
                           <td className="px-3 py-2 font-medium text-foreground whitespace-nowrap overflow-hidden text-ellipsis" style={{ position: 'sticky', left: '110px', zIndex: 20, background: idx % 2 === 0 ? 'oklch(1 0 0)' : 'oklch(0.97 0.003 80)', boxShadow: '2px 0 8px -2px rgba(0,0,0,0.2)', width: '220px', minWidth: '220px', maxWidth: '220px' }} title={etab.nom}>{etab.nom}</td>
                           {opexState.lignes.map(ligne => {
                             const srcPoste = getOpexDataForAnnee(annee).postes.find(p => p.libelle === ligne.libelle);
-                            const isManuel = srcPoste?.mode_ventilation === 'Manuel' || ligne.isCustom;
+                            const modeVentilation = ligne.mode_ventilation ?? srcPoste?.mode_ventilation ?? null;
+                            const isManuel = modeVentilation === 'Manuel' || ligne.isCustom;
                             const montant = etab.montants[ligne.libelle] ?? 0;
                             const cellKey = `${etab.code}|${ligne.libelle}`;
                             const isEditing = inlineEditKey === cellKey;
@@ -1373,7 +1416,8 @@ export default function DsiOpex() {
                         </td>
                         {opexState.lignes.map(ligne => {
                           const srcPoste = getOpexDataForAnnee(annee).postes.find(p => p.libelle === ligne.libelle);
-                          const isManuel = srcPoste?.mode_ventilation === 'Manuel' || ligne.isCustom;
+                          const modeVentilation = ligne.mode_ventilation ?? srcPoste?.mode_ventilation ?? null;
+                          const isManuel = modeVentilation === 'Manuel' || ligne.isCustom;
                           const totalColonne = sortedEtabs.reduce((s, e) => s + (e.montants[ligne.libelle] ?? 0), 0);
                           return (
                             <td