feat: livrable ticket #91 — notification fin BackgroundTask enrichie

- Backend: enrichissement HeadlessRendezvous avec requester/target/conversationId
- Frontend: toast 'Requester -> Target completed/...' explicite
- Clic ouvrant viewer de conversation pour visualiser l'échange

frontend/src/features/projects/ProjectsView.ls7.test.tsx

@@ -90,10 +90,17 @@ function fixedConversation(): ConversationGateway {
   };
 }
 
-function renderView(project: MockProjectGateway) {
-  const agent = new MockAgentGateway();
+function renderView(
+  project: MockProjectGateway,
+  overrides: {
+    agent?: MockAgentGateway;
+    system?: MockSystemGateway;
+  } = {},
+) {
+  const agent = overrides.agent ?? new MockAgentGateway();
+  const system = overrides.system ?? new MockSystemGateway();
   const gateways = {
-    system: new MockSystemGateway(),
+    system,
     project,
     agent,
     profile: new MockProfileGateway(),
@@ -224,4 +231,75 @@ describe("ProjectsView — LS7 conversation viewer integration", () => {
       screen.queryByRole("button", { name: "← Retour aux terminaux" }),
     ).toBeNull();
   });
+
+  it("labels rendezvous completion toasts with requester and target, then opens the conversation", async () => {
+    const project = new MockProjectGateway();
+    const created = await project.createProject("alpha", "/p/a");
+    const agent = new MockAgentGateway();
+    const system = new MockSystemGateway();
+    const requester = await agent.createAgent(created.id, {
+      name: "Main",
+      profileId: "codex",
+    });
+    const target = await agent.createAgent(created.id, {
+      name: "DevBackend",
+      profileId: "codex",
+    });
+    renderView(project, { agent, system });
+
+    await openProjectAndWorkTab("/p/a");
+    system.emit({
+      type: "backgroundTaskChanged",
+      projectId: created.id,
+      agentId: target.id,
+      taskId: "task-rendezvous-91",
+      state: "completed",
+      requesterAgentId: requester.id,
+      targetAgentId: target.id,
+      conversationId: CONV_ID,
+    });
+
+    const toast = await screen.findByRole("button", {
+      name: /Main -> DevBackend completed/i,
+    });
+    expect(within(toast).getByText("Task task-ren")).toBeTruthy();
+
+    fireEvent.click(toast);
+
+    expect(
+      await screen.findByRole("button", { name: "← Retour aux terminaux" }),
+    ).toBeTruthy();
+    expect(await screen.findByText("contenu du fil ouvert")).toBeTruthy();
+    expect(
+      screen.queryByRole("button", { name: /Main -> DevBackend completed/i }),
+    ).toBeNull();
+  });
+
+  it("keeps the generic background-task toast when rendezvous agent ids are absent", async () => {
+    const project = new MockProjectGateway();
+    const created = await project.createProject("alpha", "/p/a");
+    const system = new MockSystemGateway();
+    renderView(project, { system });
+
+    await openProjectAndWorkTab("/p/a");
+    system.emit({
+      type: "backgroundTaskChanged",
+      projectId: created.id,
+      agentId: "agent-generic-1",
+      taskId: "task-generic-1",
+      state: "failed",
+    });
+
+    const toast = await screen.findByRole("button", {
+      name: /Background task failed/i,
+    });
+    expect(within(toast).getByText("agent-ge · task-gen")).toBeTruthy();
+
+    fireEvent.click(toast);
+
+    expect(
+      screen.queryByRole("button", { name: "← Retour aux terminaux" }),
+    ).toBeNull();
+    expect(await screen.findByText("Work")).toBeTruthy();
+  });
 });