fix(projects): le viewer de conversation persiste au changement de layout/projet (#172)

Le viewer (CLI custom) se vidait au changement de layout/projet car l'etat viewerConversationId etait reset sur le changement de projet actif. Remplace par un etat viewerConversation {projectId, conversationId} lie a la conversation elle-meme, rendu contre le projectId de la conversation: la conversation persiste tant que la session headless existe, a l'instar de la TUI native.

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

@@ -1,8 +1,8 @@
 /**
  * LS7 — `ProjectsView` integration: clicking a conversation in the Work panel swaps
  * the terminal grid for the read-only `ConversationViewer`; the back button returns
- * to the grid; switching project resets the viewer; and with no conversation open
- * the terminal grid is shown unchanged (non-regression).
+ * to the grid; switching project preserves the viewer; and with no conversation
+ * open the terminal grid is shown unchanged (non-regression).
  */
 import { describe, it, expect } from "vitest";
 import { render, screen, fireEvent, waitFor, within } from "@testing-library/react";
@@ -100,6 +100,8 @@ function renderView(
   project: MockProjectGateway,
   overrides: {
     agent?: MockAgentGateway;
+    conversation?: ConversationGateway;
+    layout?: MockLayoutGateway;
     system?: MockSystemGateway;
   } = {},
 ) {
@@ -112,10 +114,10 @@ function renderView(
     profile: new MockProfileGateway(),
     template: new MockTemplateGateway(agent),
     git: new MockGitGateway(),
-    layout: new MockLayoutGateway(),
+    layout: overrides.layout ?? new MockLayoutGateway(),
     terminal: new MockTerminalGateway(),
     workState: fixedWorkState(),
-    conversation: fixedConversation(),
+    conversation: overrides.conversation ?? fixedConversation(),
     window: new MockWindowGateway(),
   } as unknown as Gateways;
   return render(
@@ -184,11 +186,31 @@ describe("ProjectsView — LS7 conversation viewer integration", () => {
     ).toBeNull();
   });
 
-  it("resets the viewer when the active project changes", async () => {
+  it("keeps the viewer attached to its source project when the active project changes", async () => {
     const project = new MockProjectGateway();
-    await project.createProject("alpha", "/p/a");
+    const alpha = await project.createProject("alpha", "/p/a");
     await project.createProject("beta", "/p/b");
-    renderView(project);
+    const reads: string[] = [];
+    renderView(project, {
+      conversation: {
+        readPage: async (projectId) => {
+          reads.push(projectId);
+          return {
+            turns: [
+              {
+                id: "t1",
+                atMs: 1_700_000_000_000,
+                role: "prompt",
+                source: { kind: "human" },
+                text: `contenu du fil ${projectId}`,
+                textLen: 32,
+              },
+            ],
+            hasMore: false,
+          };
+        },
+      },
+    });
 
     // Open BOTH projects as tabs. Use the projects manager window so the list
     // persists across activation (the inline welcome list is replaced by the
@@ -211,15 +233,41 @@ describe("ProjectsView — LS7 conversation viewer integration", () => {
     );
     await screen.findByRole("button", { name: "← Retour aux terminaux" });
 
-    // Switch the active project (top tab) ⇒ viewer resets to the grid.
+    // Switch the active project (top tab) ⇒ the viewer remains visible and
+    // keeps reading the conversation from the project where it was opened.
     fireEvent.click(screen.getByRole("tab", { name: "beta" }));
 
-    await waitFor(() =>
-      expect(
-        screen.queryByRole("button", { name: "← Retour aux terminaux" }),
-      ).toBeNull(),
+    expect(
+      await screen.findByRole("button", { name: "← Retour aux terminaux" }),
+    ).toBeTruthy();
+    expect(await screen.findByText(`contenu du fil ${alpha.id}`)).toBeTruthy();
+    expect(screen.queryByTestId("layout-grid")).toBeNull();
+    expect(reads.every((projectId) => projectId === alpha.id)).toBe(true);
+  });
+
+  it("keeps the viewer open when the active layout changes", async () => {
+    const project = new MockProjectGateway();
+    const alpha = await project.createProject("alpha", "/p/a");
+    const layout = new MockLayoutGateway();
+    await layout.createLayout(alpha.id, "Beta");
+    renderView(project, { layout });
+
+    await openProjectAndWorkTab("/p/a");
+    fireEvent.click(
+      await screen.findByRole("button", { name: `open conversation ${CONV_ID}` }),
     );
-    expect(await screen.findByTestId("layout-grid")).toBeTruthy();
+    expect(
+      await screen.findByRole("button", { name: "← Retour aux terminaux" }),
+    ).toBeTruthy();
+    expect(await screen.findByText("contenu du fil ouvert")).toBeTruthy();
+
+    fireEvent.click(await screen.findByRole("tab", { name: "Beta" }));
+
+    expect(
+      await screen.findByRole("button", { name: "← Retour aux terminaux" }),
+    ).toBeTruthy();
+    expect(await screen.findByText("contenu du fil ouvert")).toBeTruthy();
+    expect(screen.queryByTestId("layout-grid")).toBeNull();
   });
 
   it("shows the terminal grid unchanged when no conversation is open (non-regression)", async () => {
@@ -356,6 +404,39 @@ describe("ProjectsView — LS7 conversation viewer integration", () => {
     expect(await screen.findByText("Work")).toBeTruthy();
   });
 
+  it("does not close an open viewer when a background-task toast has no conversation", async () => {
+    const project = new MockProjectGateway();
+    const created = await project.createProject("alpha", "/p/a");
+    const system = new MockSystemGateway();
+    renderView(project, { system });
+
+    await openProjectAndWorkTab("/p/a");
+    fireEvent.click(
+      await screen.findByRole("button", { name: `open conversation ${CONV_ID}` }),
+    );
+    expect(
+      await screen.findByRole("button", { name: "← Retour aux terminaux" }),
+    ).toBeTruthy();
+
+    system.emit({
+      type: "backgroundTaskChanged",
+      projectId: created.id,
+      agentId: "agent-generic-1",
+      taskId: "task-generic-1",
+      state: "failed",
+    });
+
+    fireEvent.click(
+      await screen.findByRole("button", { name: /Background task failed/i }),
+    );
+
+    expect(
+      await screen.findByRole("button", { name: "← Retour aux terminaux" }),
+    ).toBeTruthy();
+    expect(await screen.findByText("contenu du fil ouvert")).toBeTruthy();
+    expect(screen.queryByTestId("layout-grid")).toBeNull();
+  });
+
   it("prefixes task toast context with a truncatable project-name line and falls back when unresolved", async () => {
     const project = new MockProjectGateway();
     const created = await project.createProject(