diff --git a/ajax_inscr_gestion.php b/ajax_inscr_gestion.php
index 38311c3..852523c 100644
--- a/ajax_inscr_gestion.php
+++ b/ajax_inscr_gestion.php
@@ -5,12 +5,30 @@
  */
 session_start();
 
+header('Content-Type: application/json; charset=utf-8');
+
+// Filet de securite : transforme tout fatal (include manquant, fonction
+// indefinie, parse error...) en reponse JSON exploitable au lieu d'un 500 muet.
+$GLOBALS['__inscr_gestion_done'] = false;
+register_shutdown_function(function () {
+    if (!empty($GLOBALS['__inscr_gestion_done'])) {
+        return;
+    }
+    $err = error_get_last();
+    $strDetail = ($err && in_array($err['type'], array(E_ERROR, E_PARSE, E_CORE_ERROR, E_COMPILE_ERROR), true))
+        ? ($err['message'] . ' @ ' . $err['file'] . ':' . $err['line'])
+        : 'fatal inconnu';
+    error_log('[ajax_inscr_gestion] ' . $strDetail);
+    if (!headers_sent()) {
+        http_response_code(200);
+    }
+    echo json_encode(array('state' => 'error', 'message' => 'fatal', 'detail' => $strDetail));
+});
+
 require_once 'php/inc_fonctions.php';
 require_once 'php/inc_fx_promoteur.php';
 require_once 'php/inc_fx_inscriptions_gestion.php';
 
-header('Content-Type: application/json; charset=utf-8');
-
 $intComId = intval($_SESSION['com_id'] ?? 0);
 $strAction = trim((string)($_REQUEST['a'] ?? ''));
 $strLangue = trim((string)($_REQUEST['lang'] ?? 'fr'));
@@ -19,12 +37,14 @@ if ($strLangue === '') {
 }
 
 if ($intComId <= 0) {
+    $GLOBALS['__inscr_gestion_done'] = true;
     echo json_encode(array('state' => 'error', 'message' => 'session'));
     exit;
 }
 
 $tabRetour = array('state' => 'error');
 
+try {
 switch ($strAction) {
     case 'par_statut_course':
         $intParId = intval($_REQUEST['par_id'] ?? 0);
@@ -110,8 +130,34 @@ switch ($strAction) {
         break;
 
     default:
-        $tabRetour = array('state' => 'error', 'message' => 'invalid_action');
+        // DIAGNOSTIC TEMPORAIRE : expose ce que le serveur a reellement recu
+        // pour comprendre pourquoi l'action ne matche aucun case.
+        $tabRetour = array(
+            'state'   => 'error',
+            'message' => 'invalid_action',
+            'debug'   => array(
+                'a_recu'        => $strAction,
+                'a_len'         => strlen($strAction),
+                'request_keys'  => array_keys($_REQUEST),
+                'post_keys'     => array_keys($_POST),
+                'get_keys'      => array_keys($_GET),
+                'method'        => $_SERVER['REQUEST_METHOD'] ?? '',
+                'content_type'  => $_SERVER['CONTENT_TYPE'] ?? '',
+            ),
+        );
+        error_log('[ajax_inscr_gestion] invalid_action a=' . json_encode($strAction)
+            . ' REQUEST_keys=' . json_encode(array_keys($_REQUEST))
+            . ' POST_keys=' . json_encode(array_keys($_POST)));
         break;
 }
+} catch (\Throwable $e) {
+    error_log('[ajax_inscr_gestion] ' . $e->getMessage() . ' @ ' . $e->getFile() . ':' . $e->getLine());
+    $tabRetour = array(
+        'state' => 'error',
+        'message' => 'exception',
+        'detail' => $e->getMessage() . ' @ ' . $e->getFile() . ':' . $e->getLine(),
+    );
+}
 
+$GLOBALS['__inscr_gestion_done'] = true;
 echo json_encode($tabRetour);