feat(agents): role orchestrateur du contexte global expose et configurable par agent — isOrchestrator distinct des permissions MCP, DTO update_project_orchestrator (terminologie wire legacy conservee), refus idea_context_update explicite avec writer effectif + orientation idea_context_propose, surface AgentsPanel + adaptateurs frontend — #276 (QA verte: cargo fmt/check, tests cibles application/app-tauri/infrastructure/backend, npm typecheck, 69/69 tests frontend agents/adapters)

frontend/src/features/agents/AgentsPanel.tsx

@@ -188,6 +188,11 @@ export function AgentsPanel({ projectId, projectRoot = "" }: AgentsPanelProps) {
     agentId: string;
     profileId: string;
   } | null>(null);
+  const [pendingWriterChange, setPendingWriterChange] = useState<{
+    agentId: string;
+    agentName: string;
+    currentWriterName: string;
+  } | null>(null);
 
   async function confirmProfileChange() {
     if (!pendingProfileChange) return;
@@ -204,6 +209,27 @@ export function AgentsPanel({ projectId, projectRoot = "" }: AgentsPanelProps) {
     }
   }
 
+  function requestWriterChange(agent: Agent) {
+    if (agent.isOrchestrator || vm.busy) return;
+    const currentWriter = vm.agents.find((candidate) => candidate.isOrchestrator);
+    if (currentWriter && currentWriter.id !== agent.id) {
+      setPendingWriterChange({
+        agentId: agent.id,
+        agentName: agent.name,
+        currentWriterName: currentWriter.name,
+      });
+      return;
+    }
+    void vm.updateProjectOrchestrator(agent.id);
+  }
+
+  async function confirmWriterChange() {
+    if (!pendingWriterChange) return;
+    const agentId = pendingWriterChange.agentId;
+    setPendingWriterChange(null);
+    await vm.updateProjectOrchestrator(agentId);
+  }
+
   const selectedTemplate = templates.find((t) => t.id === newTemplateId) ?? null;
   const selectedTemplateMissingProfile =
     selectedTemplate !== null && selectedTemplate.defaultProfileId.trim().length === 0;
@@ -440,6 +466,14 @@ export function AgentsPanel({ projectId, projectRoot = "" }: AgentsPanelProps) {
                   >
                     <span className="flex min-w-0 max-w-full flex-wrap items-center gap-2">
                       <span className="font-medium text-content">{a.name}</span>
+                      {a.isOrchestrator && (
+                        <span
+                          aria-label="Writer contexte"
+                          className="rounded-full border border-border-strong bg-raised px-2 py-0.5 text-xs font-medium text-content"
+                        >
+                          Writer contexte
+                        </span>
+                      )}
                       {agentDrift && (
                         <span
                           aria-label="update available"
@@ -471,6 +505,35 @@ export function AgentsPanel({ projectId, projectRoot = "" }: AgentsPanelProps) {
                     )}
                   </button>
 
+                  {isSelected && (
+                    <section
+                      aria-label={`Rôle dans le projet — ${a.name}`}
+                      className="rounded-md border border-border bg-surface p-3"
+                    >
+                      <h4 className="text-xs font-semibold uppercase tracking-wide text-muted">
+                        Rôle dans le projet
+                      </h4>
+                      <label className="mt-2 flex cursor-pointer items-start gap-2">
+                        <input
+                          type="radio"
+                          name="project-context-writer"
+                          aria-label={`Writer du contexte projet global pour ${a.name}`}
+                          checked={a.isOrchestrator === true}
+                          disabled={vm.busy}
+                          onChange={() => requestWriterChange(a)}
+                          className="mt-0.5"
+                        />
+                        <span className="text-sm font-medium text-content">
+                          Writer du contexte projet global
+                        </span>
+                      </label>
+                      <p className="mt-1 pl-5 text-xs text-muted">
+                        Peut modifier directement le contexte partagé du projet.
+                        Un seul agent peut avoir ce rôle.
+                      </p>
+                    </section>
+                  )}
+
                   {limitState && (
                     <AgentLimitBadge
                       state={limitState}
@@ -747,6 +810,44 @@ export function AgentsPanel({ projectId, projectRoot = "" }: AgentsPanelProps) {
           </div>
         </div>
       )}
+
+      {pendingWriterChange && (
+        <div
+          role="dialog"
+          aria-modal="true"
+          aria-label="Confirmer le changement de writer contexte"
+          className="fixed inset-0 z-50 flex items-center justify-center bg-black/55 p-4"
+        >
+          <div className="w-full max-w-sm rounded-lg border border-border bg-surface p-5 shadow-xl">
+            <h4 className="text-sm font-semibold text-content">
+              Changer le writer du contexte
+            </h4>
+            <p className="mt-2 text-sm text-muted">
+              Le rôle sera retiré de {pendingWriterChange.currentWriterName} et
+              attribué à {pendingWriterChange.agentName}. Continuer&nbsp;?
+            </p>
+            <div className="mt-4 flex items-center justify-end gap-2">
+              <Button
+                variant="ghost"
+                aria-label="Annuler le changement de writer contexte"
+                disabled={vm.busy}
+                onClick={() => setPendingWriterChange(null)}
+              >
+                Annuler
+              </Button>
+              <Button
+                variant="primary"
+                aria-label="Confirmer le changement de writer contexte"
+                loading={vm.busy}
+                disabled={vm.busy}
+                onClick={() => void confirmWriterChange()}
+              >
+                Continuer
+              </Button>
+            </div>
+          </div>
+        </div>
+      )}
     </Panel>
   );
 }