diff --git a/delphi-backend/UMainForm.pas b/delphi-backend/UMainForm.pas
index bfedfbd..de0a255 100644
--- a/delphi-backend/UMainForm.pas
+++ b/delphi-backend/UMainForm.pas
@@ -2000,7 +2000,7 @@ begin
   LogLine('Windows session locked / suspend — notifying JS');
   WebBrowser.ExecuteJavaScript(
     'if(window.Bridge&&typeof Bridge.onSystemLock==="function")Bridge.onSystemLock();' +
-    'else if(typeof lockVault==="function")lockVault()');
+    'else if(typeof lockVault==="function")lockVault("Windows session locked or computer asleep")');
 end;
 
 procedure TMainForm.BridgeTrayRestore;
@@ -2018,7 +2018,7 @@ begin
   // User picked "Lock vault" from the tray menu. Trigger lockVault() in
   // JS — same path as the WTS_SESSION_LOCK auto-lock.
   LogLine('Lock requested from tray menu');
-  WebBrowser.ExecuteJavaScript('if(typeof lockVault==="function")lockVault()');
+  WebBrowser.ExecuteJavaScript('if(typeof lockVault==="function")lockVault("tray menu")');
 end;
 
 procedure TMainForm.BridgeQuit;
diff --git a/js/app.autofill.js b/js/app.autofill.js
index 1b144fe..6a51bac 100644
--- a/js/app.autofill.js
+++ b/js/app.autofill.js
@@ -268,7 +268,14 @@ async function autofillHandleRequest(windowTitle, kind) {
                 else                     pwd.focus();
             }
         }, 80);
-        toast('Vault is locked — unlock to autofill', 'warning');
+        // LA RAISON AVEC LE MESSAGE. Sans dernier verrouillage connu, c'est que
+        // cette page n'a jamais ete deverrouillee - rechargee entre-temps, ou
+        // jamais ouverte : l'heure de chargement le tranche.
+        toast('Vault is locked — unlock to autofill ('
+              + (state.lastLockReason
+                    ? 'locked by: ' + state.lastLockReason
+                    : 'never unlocked since the page loaded at ' + state.pageLoadedAt)
+              + ')', 'warning');
         return;
     }
 
diff --git a/js/app.js b/js/app.js
index 7eeeaf5..ca88cff 100644
--- a/js/app.js
+++ b/js/app.js
@@ -95,7 +95,8 @@ const Bridge = (() => {
                     toast('System lock — vault kept unlocked (quick unlock active)');
                 return;
             }
-            if (typeof lockVault === 'function') lockVault();
+            if (typeof lockVault === 'function')
+                lockVault('Windows session locked or computer asleep');
         },
 
         // Called by Delphi (ExecuteJavaScript) when the user restores the
@@ -732,6 +733,12 @@ const state = {
     selectedId: null,
     theme:     localStorage.getItem('theme') || 'dark',
     locked:    false,        // true after user clicks Lock (token still valid server-side)
+    // POURQUOI LE COFFRE S'EST FERME, et depuis quand la page vit. Un
+    // verrouillage automatique etait muet ; quand le remplissage repondait
+    // "Vault is locked", rien ne disait si c'etait l'inactivite, une veille de
+    // Windows, ou une page rechargee qui avait tout perdu.
+    lastLockReason: '',
+    pageLoadedAt:   new Date().toLocaleTimeString(),
     autoLock:  parseInt(localStorage.getItem('autoLockMin') || '5'),
     askBeforeDelete: localStorage.getItem('askBeforeDelete') !== '0',  // default true
     maskUsernames:   localStorage.getItem('maskUsernames')   === '1',  // default false
@@ -1424,7 +1431,8 @@ async function confirmDiscardForSessionExit(action) {
     });
 }
 
-function lockVault() {
+function lockVault(reason) {
+    state.lastLockReason = (reason || 'manual lock') + ' at ' + new Date().toLocaleTimeString();
     sessionStorage.removeItem('cryptoKey');
     state.cryptoKey = null;
     state.entries = [];
@@ -7010,7 +7018,7 @@ function resetAutoLock() {
     autoLockTimer = setTimeout(() => {
         hideIdleWarning();
         toast('Auto-locked due to inactivity', 'warning');
-        lockVault();
+        lockVault('inactivity (' + state.autoLock + ' min)');
     }, totalMs);
 }
 
@@ -7185,7 +7193,7 @@ async function enterApp() {
         if (!ok) {
             const fresh = await bridgePinStatus();
             state.pinConfigured = fresh;
-            lockVault();
+            lockVault('wrong PIN after the master password');
             $('#authHint').textContent = fresh
                 ? 'Wrong PIN. Try again.'
                 : 'Too many wrong PIN attempts — PIN has been removed. Re-set it from Settings after unlocking.';