fix(application,domain,infrastructure,web-server,app-tauri,frontend): arrêt d'agent fiable avec cascade sur l'arbre de propriété et statut cohérent — #320 (QA verte)

Symptôme: stopper un agent (ex Main sur UnityPlugin) laissait des travaux
poursuivre, la cascade n'atteignait pas les agents lancés et la pastille
restait orange pendant que l'agent continuait à en appeler d'autres.

- barrière d'admission par génération d'exécution (ExecutionControl): un stop
  ferme l'admission de tout le sous-arbre propriété/attente AVANT toute
  annulation asynchrone — plus aucune nouvelle action inter-agents après stop
- arbre de propriété durable en-process (launched_by) + dépendances d'attente
  actives: la cascade couvre transitivement agents et travaux lancés
- commandes d'un agent arrêté rejetées (AppError::AgentStopped); stop
  lui-même admis pour rester idempotent; réactivation sur relance humaine
  (génération +1) et enregistrement du propriétaire au spawn
- admission exposée aux adaptateurs hors commandes cœur (tickets, templates,
  plugins) via ensure_agent_execution_active; MCP server/tools, web-server et
  commandes Tauri alignés
- cohérence live-state: statut Idle avec intent « Arrêté » ou
  « Arrêt incomplet — Certains travaux sont encore actifs » selon l'issue de
  la cascade; workstate et surfaces UI (AgentsPanel, LayoutGrid,
  ProjectWorkStatePanel) reflètent l'état réel, plus de pastille orange fantôme
- tests: orchestrator_service (cascade/générations/idempotence),
  workstate_actions, background_task_cancel, error_codes, agents, layout,
  workstate

QA verte sur fix/320-agent-stop-cascade. Aucun push.

frontend/src/features/layout/LayoutGrid.test.tsx

@@ -259,6 +259,60 @@ describe("LayoutGrid (with MockLayoutGateway)", () => {
     expect(screen.queryByText("Idle")).toBeNull();
   });
 
+  it("removes the orange busy veil when backend live-state reports stopping", async () => {
+    const layout = new MockLayoutGateway();
+    const agent = new MockAgentGateway();
+    const workState = new MockWorkStateGateway();
+    const created = await agent.createAgent("p1", {
+      name: "StoppingAgent",
+      profileId: "prof-1",
+    });
+    const tree = await layout.loadLayout("p1");
+    const leafId = leaves(tree)[0].id;
+    await layout.mutateLayout("p1", {
+      type: "setCellAgent",
+      target: leafId,
+      agent: created.id,
+    });
+    await layout.mutateLayout("p1", {
+      type: "setSession",
+      target: leafId,
+      session: "stopping-session",
+    });
+    workState._setProjectWorkState("p1", {
+      agents: [
+        {
+          agentId: created.id,
+          name: "StoppingAgent",
+          profileId: "prof-1",
+          runtimeState: "stopping",
+          live: {
+            nodeId: leafId,
+            sessionId: "stopping-session",
+            kind: "pty",
+            runtimeState: "stopping",
+          },
+          busy: { state: "busy", ticket: "stale-ticket", sinceMs: 1 },
+          tickets: [],
+        },
+      ],
+      conversations: [],
+    });
+
+    render(
+      <DIProvider gateways={{ layout, agent, workState } as unknown as Gateways}>
+        <LayoutGrid projectId="p1" cwd="/home/me/proj" />
+      </DIProvider>,
+    );
+
+    await waitFor(() =>
+      expect(screen.queryByTestId("agent-cell-runtime-loading")).toBeNull(),
+    );
+    expect(screen.queryByTestId("target-announcements-overlay")).toBeNull();
+    expect(screen.queryByLabelText("StoppingAgent arrêté")).toBeNull();
+    expect(screen.getByTestId("terminal-view")).toBeTruthy();
+  });
+
   it("relaunches a stopped agent from scratch in the same cell", async () => {
     const layout = new MockLayoutGateway();
     const agent = new MockAgentGateway();

frontend/src/features/layout/LayoutGrid.tsx

@@ -847,6 +847,9 @@ function LeafView({
   const agentWork = agentId
     ? workState?.agents.find((row) => row.agentId === agentId)
     : undefined;
+  const runtimeState = agentWork?.runtimeState;
+  const stoppingOrStopped =
+    runtimeState === "stopping" || runtimeState === "stopped";
   const activeTicket = agentWork?.tickets.find((ticket) => ticket.status === "inProgress");
   const queuedTickets = agentWork?.tickets.filter((ticket) => ticket.status === "queued") ?? [];
   const inboxDepth = Math.max(
@@ -858,9 +861,12 @@ function LeafView({
     agentWork?.backgroundTasks?.filter((task) =>
       task.status === "completed" || task.status === "failed" || task.status === "cancelled",
     ) ?? [];
-  const busyByWorkState = agentWork?.busy.state === "busy" || Boolean(activeTicket);
+  const busyByWorkState =
+    !stoppingOrStopped &&
+    (agentWork?.busy.state === "busy" || Boolean(activeTicket));
   const delegatedTicket = activeTicket?.source.kind === "agent" ? activeTicket : undefined;
-  const busyActive = announcementBusyActive || busyByWorkState;
+  const busyActive =
+    !stoppingOrStopped && (announcementBusyActive || busyByWorkState);
   const [cellRestart, setCellRestart] = useState<CellRestartState | null>(null);
   const cellRestartRef = useRef<CellRestartState | null>(null);
   const cellRestartRequestRef = useRef(0);
@@ -938,7 +944,6 @@ function LeafView({
   const [restartError, setRestartError] = useState(false);
   const [freshRestartedSession, setFreshRestartedSession] =
     useState<FreshRestartedSession | null>(null);
-  const runtimeState = agentWork?.runtimeState;
   const livePinnedAgent = agentId
     ? liveAgents.find((la) => la.agentId === agentId)
     : undefined;
@@ -1762,7 +1767,7 @@ function LeafView({
             an availability veil showing its live réflexions. Native TUI cells
             need the full-cell guard; custom CLI cells keep the canonical busy
             badge and composer lock only, matching their normal chat turn flow. */}
-        {!cellRestart && !otherRestartActive && !modelServerOverlay && cellMode !== "custom" && agentId != null && (
+        {!cellRestart && !otherRestartActive && !modelServerOverlay && !stoppingOrStopped && cellMode !== "custom" && agentId != null && (
           <TargetAnnouncementsOverlay
             projectId={projectId}
             agentId={agentId}