test(sessions): mock feature flag in ContextUsageIndicator test

Gating the cost readout behind useFeatureFlag made the component call
useService(FEATURE_FLAGS), which throws in the test's provider-less
render. Mock the hook (matching the pattern used across the UI test
suite) and add a case covering the cost suffix when the flag is on.

Generated-By: PostHog Code
Task-Id: f6d673c3-965e-4598-a4bd-663f2651a5a5

Author: gantoine

packages/ui/src/features/sessions/components/ContextUsageIndicator.test.tsx

@@ -1,9 +1,18 @@
 import type { ContextUsage } from "@posthog/ui/features/sessions/hooks/useContextUsage";
 import { Theme } from "@radix-ui/themes";
 import { render, screen } from "@testing-library/react";
-import { describe, expect, it } from "vitest";
+import { beforeEach, describe, expect, it, vi } from "vitest";
 import { ContextUsageIndicator } from "./ContextUsageIndicator";
 
+const flagState = vi.hoisted(() => ({ enabled: false }));
+vi.mock("@posthog/ui/features/feature-flags/useFeatureFlag", () => ({
+  useFeatureFlag: () => flagState.enabled,
+}));
+
+beforeEach(() => {
+  flagState.enabled = false;
+});
+
 function usage(overrides?: Partial<ContextUsage>): ContextUsage {
   return {
     used: 50_000,
@@ -53,6 +62,18 @@ describe("ContextUsageIndicator", () => {
     ).toBeInTheDocument();
   });
 
+  it("appends the estimated cost to the label when the flag is enabled", () => {
+    flagState.enabled = true;
+    render(
+      <Theme>
+        <ContextUsageIndicator
+          usage={usage({ cost: { amount: 0.42, currency: "USD" } })}
+        />
+      </Theme>,
+    );
+    expect(screen.getByText(/50K\/200K · 25% · \$0\.42/)).toBeInTheDocument();
+  });
+
   it("renders a finite stroke offset at 0% (no NaN/Infinity)", () => {
     const { container } = render(
       <Theme>