feat(cli): commande /profile + sélection de profil avec reset de session confirmé — #164 (QA verte)

Ajoute /profile comme commande slash first-class dont la sémantique de reset
de session reste explicite et testable, séparée de la palette générique :

- domain + application: /profile est enregistrée et renvoie un effet
  SlashCommandEffect::ProfileSwitch { session_id }. La commande ne reset pas
  directement : elle délègue l'effet au frontend pour imposer une confirmation.
- frontend (CustomAgentChatView): à l'exécution de /profile, ouverture d'un
  popup de sélection de profil informant que la validation reset la session,
  avec confirmation explicite (confirmedReset) requise avant changeAgentProfile.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/features/agents/CustomAgentChatView.test.tsx

@@ -522,6 +522,129 @@ describe("CustomAgentChatView", () => {
     expect(screen.queryByRole("listbox", { name: "suggestions commandes slash" })).toBeNull();
   });
 
+  it("executes /profile as a confirmed profile-switch flow that resets the current session", async () => {
+    const agent = {
+      launchAgentChat: vi.fn(async () => ({
+        sessionId: "chat-session-2",
+        cellKind: "chat" as const,
+        assignedConversationId: "conversation-2",
+      })),
+      reattachAgentChat: vi.fn(async (sessionId: string) => ({
+        sessionId,
+        scrollback: [],
+      })),
+      sendAgentChat: vi.fn(async () => {}),
+      executeSlashCommand: vi.fn(async () => ({
+        command: {
+          name: "/profile",
+          shortDescription: "Changer le profil de l'agent",
+          requiresConfirmation: true,
+          availability: { status: "available" as const },
+          source: "native" as const,
+          native: "profile" as const,
+        },
+        effect: {
+          kind: "profileSwitch" as const,
+          sessionId: "chat-session-1",
+        },
+      })),
+      changeAgentProfile: vi.fn(async () => ({ agent: { id: "agent-1" } })),
+      cancelAgentChat: vi.fn(async () => {}),
+      closeAgentChat: vi.fn(async () => {}),
+    };
+    const profileGateway = {
+      listProfiles: vi.fn(async () => [
+        profile,
+        {
+          ...profile,
+          id: "codex-high",
+          name: "Codex High",
+        },
+      ]),
+    };
+    const onSessionId = vi.fn();
+    const onConversationId = vi.fn();
+
+    render(
+      <DIProvider
+        gateways={{
+          agent,
+          profile: profileGateway,
+          system: { pickFile: vi.fn(async () => null) },
+        } as unknown as Gateways}
+      >
+        <CustomAgentChatView
+          projectId="project-1"
+          agentId="agent-1"
+          agentName="Worker"
+          profile={profile}
+          cwd="/repo"
+          nodeId="node-1"
+          sessionId="chat-session-1"
+          conversationId="conversation-1"
+          onSessionId={onSessionId}
+          onConversationId={onConversationId}
+        />
+      </DIProvider>,
+    );
+
+    await waitFor(() =>
+      expect(agent.reattachAgentChat).toHaveBeenCalledWith(
+        "chat-session-1",
+        expect.any(Function),
+      ),
+    );
+
+    const composer = screen.getByLabelText(/message CLI custom/) as HTMLTextAreaElement;
+    fireEvent.change(composer, { target: { value: "/profile" } });
+    fireEvent.keyDown(composer, { key: "Enter" });
+
+    const dialog = await screen.findByRole("dialog", { name: "Changer de profil" });
+    expect(dialog.textContent).toContain("réinitialiser la session courante");
+    expect(dialog.textContent).toContain("L'historique de cette CLI custom sera perdu");
+    expect(agent.executeSlashCommand).toHaveBeenCalledWith("/profile", {
+      sessionId: "chat-session-1",
+    });
+    expect(agent.sendAgentChat).not.toHaveBeenCalled();
+
+    const confirmButton = screen.getByRole("button", {
+      name: "Reset et changer le profil",
+    }) as HTMLButtonElement;
+    expect(confirmButton.disabled).toBe(true);
+
+    fireEvent.change(screen.getByLabelText("profil cible"), {
+      target: { value: "codex-high" },
+    });
+    fireEvent.click(screen.getByLabelText("Je confirme que la session courante sera reset."));
+    expect(confirmButton.disabled).toBe(false);
+    fireEvent.click(confirmButton);
+
+    await waitFor(() =>
+      expect(agent.changeAgentProfile).toHaveBeenCalledWith(
+        "project-1",
+        "agent-1",
+        "codex-high",
+        24,
+        80,
+      ),
+    );
+    await waitFor(() =>
+      expect(agent.launchAgentChat).toHaveBeenCalledWith("project-1", "agent-1", {
+        cwd: "/repo",
+        rows: 24,
+        cols: 80,
+        conversationId: undefined,
+        nodeId: "node-1",
+      }),
+    );
+    expect(onSessionId).toHaveBeenCalledWith(null);
+    expect(onConversationId).toHaveBeenCalledWith(null);
+    expect(onSessionId).toHaveBeenCalledWith("chat-session-2");
+    expect(onConversationId).toHaveBeenCalledWith("conversation-2");
+    expect(screen.getByText("Profil changé vers Codex High.")).toBeTruthy();
+    expect(screen.queryByRole("dialog", { name: "Changer de profil" })).toBeNull();
+  });
+
   it("pastes a clipboard image as a removable preview chip", async () => {
     const agent = {
       launchAgentChat: vi.fn(),