feat(frontend): groupes repliables par plugin pour skills et tools MCP, bouton Joindre harmonisé avec Envoyer — nouveau composant PluginContributionGroup (en-tête cliquable aria-expanded/aria-controls, badge Chargé/Non chargé, compteur de contributions, replié par défaut pour les plugins non loadés, dépliage forcé pendant la recherche) adopté par SkillsPanel et McpToolPermissionsPanel avec déduplication des plugins — #367 ; bouton Joindre du chat aligné sur le format d'Envoyer (size md, variante secondary, état loading « Ajout… », aria-label dédié, conteneur custom-agent-chat-composer-actions avec data-busy, Stop aligné md, container queries 419.99px en colonne et 279.99px wrap puis pleine largeur en busy) — #368 (QA verte: npm test ciblé ProjectPluginSettings + skills + McpToolPermissionsPanel + CustomAgentChatView + visibleSourceScan 5 fichiers 152 tests OK, Firefox headless layout 600/360/240 et busy 240 PASS, npm run build OK, git diff --check OK)

frontend/src/features/agents/CustomAgentChatView.tsx

@@ -1093,6 +1093,7 @@ export function CustomAgentChatView({
       ? (chatAttachmentDraftCache.get(initialAttachmentCacheKey) ?? [])
       : [],
   );
+  const [attachmentPicking, setAttachmentPicking] = useState(false);
   const [queuedMessages, setQueuedMessages] = useState<QueuedChatMessage[]>(
     () => chatMessageQueueCache.get(initialMessageQueueKey) ?? [],
   );
@@ -2597,16 +2598,21 @@ export function CustomAgentChatView({
   }
 
   async function pickAttachment() {
-    const path = await system.pickFile();
-    if (path) {
-      setAttachments((prev) => [
-        ...prev,
-        {
-          id: `path-${Date.now()}-${Math.random().toString(36).slice(2)}`,
-          label: pathBasename(path),
-          input: { path, sourceKind: "localFile" },
-        },
-      ]);
+    setAttachmentPicking(true);
+    try {
+      const path = await system.pickFile();
+      if (path) {
+        setAttachments((prev) => [
+          ...prev,
+          {
+            id: `path-${Date.now()}-${Math.random().toString(36).slice(2)}`,
+            label: pathBasename(path),
+            input: { path, sourceKind: "localFile" },
+          },
+        ]);
+      }
+    } finally {
+      setAttachmentPicking(false);
     }
   }
 
@@ -3608,8 +3614,8 @@ export function CustomAgentChatView({
             {composerHistoryWarning}
           </p>
         )}
-        <div className="flex min-w-0 items-end gap-2">
-          <div className="relative flex min-w-0 flex-1">
+        <div className="custom-agent-chat-composer flex min-w-0 items-end gap-2">
+          <div className="custom-agent-chat-composer-editor relative flex min-w-0 flex-1">
             <textarea
               ref={composerRef}
               aria-label={`${tr("Message CLI personnalisée", "Custom CLI message")} ${domId}`}
@@ -3677,39 +3683,47 @@ export function CustomAgentChatView({
               ↕
             </button>
           </div>
-          <Button
-            size="sm"
-            variant="ghost"
-            className="shrink-0 whitespace-nowrap"
-            disabled={!supported || opening || Boolean(savedConversationLoadFailure)}
-            onClick={() => void pickAttachment()}
+          <div
+            className="custom-agent-chat-composer-actions flex shrink-0 items-end gap-2"
+            data-busy={effectiveBusy ? "true" : "false"}
           >
-            {t("custom.attach")}
-          </Button>
-          {effectiveBusy && (
             <Button
-              size="sm"
-              variant="danger"
-              className="min-h-11 shrink-0 whitespace-nowrap"
-              disabled={!supported || !currentSession || !agent.cancelAgentChat || stopping}
-              loading={stopping}
-              title={t("custom.stop")}
-              aria-label={t("custom.stop")}
-              onClick={() => void stopCurrentRequest()}
+              size="md"
+              variant="secondary"
+              className="custom-agent-chat-composer-action min-h-11 whitespace-nowrap"
+              aria-label={tr("Joindre un fichier", "Attach a file")}
+              disabled={!supported || opening || attachmentPicking || Boolean(savedConversationLoadFailure)}
+              loading={attachmentPicking}
+              onClick={() => void pickAttachment()}
             >
-              {stopping ? t("custom.stopping") : t("custom.stop")}
+              {attachmentPicking ? tr("Ajout…", "Adding…") : t("custom.attach")}
             </Button>
-          )}
-          <Button
-            size="sm"
-            className="min-h-11 shrink-0 whitespace-nowrap"
-            disabled={!canSubmit}
-            onClick={() => void send()}
-          >
-            {effectiveBusy
-              ? tr("Mettre en attente", "Queue message")
-              : t("custom.send")}
-          </Button>
+            {effectiveBusy && (
+              <Button
+                size="md"
+                variant="danger"
+                className="custom-agent-chat-composer-action min-h-11 whitespace-nowrap"
+                disabled={!supported || !currentSession || !agent.cancelAgentChat || stopping}
+                loading={stopping}
+                title={t("custom.stop")}
+                aria-label={t("custom.stop")}
+                onClick={() => void stopCurrentRequest()}
+              >
+                {stopping ? t("custom.stopping") : t("custom.stop")}
+              </Button>
+            )}
+            <Button
+              size="md"
+              variant="primary"
+              className="custom-agent-chat-composer-action min-h-11 whitespace-nowrap"
+              disabled={!canSubmit}
+              onClick={() => void send()}
+            >
+              {effectiveBusy
+                ? tr("Mettre en attente", "Queue message")
+                : t("custom.send")}
+            </Button>
+          </div>
         </div>
       </div>
     </div>