fix(frontend): la conversation survit au redemarrage agent et a l'aller-retour projet — #291 (ProjectsView/WebWorkspace conservent le pointeur viewerConversation mais ne rendent le viewer que si sa conversation appartient au projet actif: le projet intermediaire affiche sa propre surface sans fuite, le retour au projet source remonte la vue avec la meme cle project/conversation et relit le transcript persiste; useConversationThread ne vide plus le buffer au changement de conversation cible, un contenu deja visible reste affiche pendant relecture ou echec; l'erreur de lecture devient "Impossible de recharger la conversation." avec bouton Reessayer branchant refreshTail sans retirer les tours visibles; QA verte reconfirmee par Git: ProjectsView.ls7 scenario "rehydrates the same conversation" (restart agent, switch alpha->beta->alpha, deux readPage identiques sur {projectId, conversationId}), ConversationViewer + useConversationThread 19/19, npm run build, git diff --check; reserves hors perimetre preexistantes: 3 echecs historiques ProjectsView.ls7 (helper panneau Work/open conversation) + 1 echec WebDesktopWorkspace (libelle anglais Project context); validation runtime AppImage/live restante; aucun push)

frontend/src/features/conversations/ConversationViewer.test.tsx

@@ -4,7 +4,7 @@
  * states, scroll-up "load older" trigger, and the back button (`onClose`).
  */
 import { describe, it, expect, vi } from "vitest";
-import { render, screen, fireEvent } from "@testing-library/react";
+import { render, screen, fireEvent, within } from "@testing-library/react";
 import type { ReactNode } from "react";
 
 import { DIProvider } from "@/app/di";
@@ -256,7 +256,12 @@ describe("ConversationViewer", () => {
     };
     renderViewer({ conversation: failing });
     const alert = await screen.findByRole("alert");
-    expect(alert.textContent).toContain("lecture impossible");
+    expect(alert.textContent).toContain(
+      "Impossible de recharger la conversation.",
+    );
+    expect(
+      within(alert).getByRole("button", { name: "Réessayer" }),
+    ).toBeTruthy();
   });
 
   it("offers a 'load older' control when more turns exist and triggers loadOlder", async () => {

frontend/src/features/conversations/ConversationViewer.tsx

@@ -288,12 +288,20 @@ export function ConversationViewer({
 
       {/* ── Error ── */}
       {vm.error && (
-        <p
+        <div
           role="alert"
-          className="mx-4 mt-2 shrink-0 rounded-md border border-danger/40 bg-danger/10 px-3 py-2 text-sm text-danger"
+          className="mx-4 mt-2 flex shrink-0 items-center justify-between gap-3 rounded-md border border-danger/40 bg-danger/10 px-3 py-2 text-sm text-danger"
         >
-          {vm.error}
+          <span>Impossible de recharger la conversation.</span>
-        </p>
+          <Button
+            size="sm"
+            variant="ghost"
+            onClick={() => void vm.refreshTail()}
+            loading={vm.busy}
+          >
+            Réessayer
+          </Button>
+        </div>
       )}
 
       {/* ── Thread ── */}

frontend/src/features/conversations/useConversationThread.ts

@@ -151,10 +151,9 @@ export function useConversationThread(
 
   // (Re)open whenever the target conversation changes.
   useEffect(() => {
-    setBuffer([]);
     setHasMore(false);
     void open();
-  }, [open, setBuffer]);
+  }, [open]);
 
   return { turns, busy, error, hasMore, loadOlder, refreshTail };
 }

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

@@ -1,8 +1,9 @@
 /**
  * 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 preserves the viewer; and with no conversation
+ * to the grid; switching away hides the viewer and returning rehydrates it from the
- * open the terminal grid is shown unchanged (non-regression).
+ * persisted transcript; 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";
@@ -186,15 +187,17 @@ describe("ProjectsView — LS7 conversation viewer integration", () => {
     ).toBeNull();
   });
 
-  it("keeps the viewer attached to its source project when the active project changes", async () => {
+  it("rehydrates the same conversation after an agent restart and a project roundtrip", async () => {
     const project = new MockProjectGateway();
     const alpha = await project.createProject("alpha", "/p/a");
     await project.createProject("beta", "/p/b");
-    const reads: string[] = [];
+    const system = new MockSystemGateway();
+    const reads: Array<{ projectId: string; conversationId: string }> = [];
     renderView(project, {
+      system,
       conversation: {
-        readPage: async (projectId) => {
+        readPage: async (projectId, conversationId) => {
-          reads.push(projectId);
+          reads.push({ projectId, conversationId });
           return {
             turns: [
               {
@@ -225,24 +228,57 @@ describe("ProjectsView — LS7 conversation viewer integration", () => {
     }
     await waitFor(() => expect(screen.getAllByRole("tab")).toHaveLength(2));
 
-    // Make alpha the active tab, then open its conversation viewer.
+    // Make alpha the active tab, then open its persisted conversation from a
+    // completion event carrying the stable conversation pointer.
     fireEvent.click(screen.getByRole("tab", { name: "alpha" }));
-    openPanel("Work state");
+    system.emit({
+      type: "backgroundTaskChanged",
+      projectId: alpha.id,
+      agentId: "agent-1",
+      taskId: "task-rehydrate-291",
+      state: "completed",
+      conversationId: CONV_ID,
+    });
     fireEvent.click(
-      await screen.findByRole("button", { name: `open conversation ${CONV_ID}` }),
+      await screen.findByRole("button", { name: /Background task completed/i }),
     );
     await screen.findByRole("button", { name: "← Retour aux terminaux" });
+    await screen.findByText(`contenu du fil ${alpha.id}`);
 
-    // Switch the active project (top tab) ⇒ the viewer remains visible and
+    // Simulate the successful self-restart lifecycle. It must not replace the
-    // keeps reading the conversation from the project where it was opened.
+    // persisted conversation pointer with a fresh live buffer.
+    system.emit({
+      type: "agentRestartRequested",
+      agentId: "agent-1",
+      restartId: "restart-291",
+      reason: null,
+    });
+    system.emit({
+      type: "agentRestartCompleted",
+      agentId: "agent-1",
+      restartId: "restart-291",
+    });
+
+    // Switching away shows beta's own surface instead of leaking alpha's viewer.
     fireEvent.click(screen.getByRole("tab", { name: "beta" }));
+    expect(await screen.findByTestId("layout-grid")).toBeTruthy();
+    expect(
+      screen.queryByRole("button", { name: "← Retour aux terminaux" }),
+    ).toBeNull();
 
+    // Returning remounts the viewer and reloads the persisted transcript with
+    // exactly the same project/conversation identity.
+    fireEvent.click(screen.getByRole("tab", { name: "alpha" }));
     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);
+    await waitFor(() => expect(reads).toHaveLength(2));
+    expect(reads).toEqual([
+      { projectId: alpha.id, conversationId: CONV_ID },
+      { projectId: alpha.id, conversationId: CONV_ID },
+    ]);
   });
 
   it("keeps the viewer open when the active layout changes", async () => {

frontend/src/features/projects/ProjectsView.tsx

@@ -247,6 +247,8 @@ export function ProjectsView() {
   const [taskToasts, setTaskToasts] = useState<BackgroundTaskToast[]>([]);
 
   const active = vm.openTabs.find((t) => t.id === vm.activeTabId) ?? null;
+  const activeViewerConversation =
+    viewerConversation?.projectId === active?.id ? viewerConversation : null;
   const projectNameById = useMemo(() => {
     const names = new Map<string, string>();
     for (const project of vm.projects) names.set(project.id, project.name);
@@ -924,11 +926,11 @@ export function ProjectsView() {
               projectId={active.id}
               onActiveLayoutChange={setActiveLayout}
             />
-            {viewerConversation ? (
+            {activeViewerConversation ? (
               <ConversationViewer
-                key={`${viewerConversation.projectId}-${viewerConversation.conversationId}`}
+                key={`${activeViewerConversation.projectId}-${activeViewerConversation.conversationId}`}
-                projectId={viewerConversation.projectId}
+                projectId={activeViewerConversation.projectId}
-                conversationId={viewerConversation.conversationId}
+                conversationId={activeViewerConversation.conversationId}
                 onClose={() => setViewerConversation(null)}
                 onOpenConversation={openConversation}
               />
@@ -953,14 +955,6 @@ export function ProjectsView() {
               </AnnouncementsProvider>
             )}
           </>
-        ) : viewerConversation ? (
-          <ConversationViewer
-            key={`${viewerConversation.projectId}-${viewerConversation.conversationId}`}
-            projectId={viewerConversation.projectId}
-            conversationId={viewerConversation.conversationId}
-            onClose={() => setViewerConversation(null)}
-            onOpenConversation={openConversation}
-          />
         ) : (
           <div className="flex flex-1 justify-center overflow-y-auto p-6">
             <div className="w-full max-w-xl">

frontend/src/features/web/WebWorkspace.tsx

@@ -279,9 +279,13 @@ function WebDesktopWorkspace({
 
   useEffect(() => {
     setActiveLayout(null);
-    setViewerConversation(null);
   }, [openId]);
 
+  const activeViewerConversation =
+    viewerConversation?.projectId === openProject?.id
+      ? viewerConversation
+      : null;
+
   function setPlacement(panel: WebDesktopPanelId, placement: Exclude<ViewPlacement, "detached">) {
     setPlacements((prev) => {
       const next: WebDesktopPlacements = { ...prev };
@@ -535,11 +539,11 @@ function WebDesktopWorkspace({
                 projectId={openProject.id}
                 onActiveLayoutChange={setActiveLayout}
               />
-              {viewerConversation ? (
+              {activeViewerConversation ? (
                 <ConversationViewer
-                  key={`${viewerConversation.projectId}-${viewerConversation.conversationId}`}
+                  key={`${activeViewerConversation.projectId}-${activeViewerConversation.conversationId}`}
-                  projectId={viewerConversation.projectId}
+                  projectId={activeViewerConversation.projectId}
-                  conversationId={viewerConversation.conversationId}
+                  conversationId={activeViewerConversation.conversationId}
                   onClose={() => setViewerConversation(null)}
                   onOpenConversation={openConversation}
                 />