test(canvas/mobile): add palette-context coverage (9 cases)

Covers MobileAccentProvider + usePalette hook:
- Renders children
- usePalette(dark=false) → MOL_LIGHT
- usePalette(dark=true)  → MOL_DARK
- accent=null returns base palette unchanged
- accent=base.accent returns base palette unchanged (identity guard)
- accent=#custom → accent + online overridden
- MOL_LIGHT/MOL_DARK singletons never mutated

The pure functions (getPalette, normalizeStatus, tierCode) are already
covered by palette.test.ts — only the React context/hook is new here.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

canvas/src/components/mobile/__tests__/palette-context.test.tsx

@@ -0,0 +1,131 @@
+// @vitest-environment jsdom
+/**
+ * palette-context: MobileAccentProvider + usePalette hook coverage.
+ *
+ * Covers:
+ *   - usePalette(dark=false) without provider → MOL_LIGHT
+ *   - usePalette(dark=true)  without provider → MOL_DARK
+ *   - usePalette with provider accent=null        → base palette unchanged
+ *   - usePalette with provider accent=base.accent → base palette unchanged (identity guard)
+ *   - usePalette with provider accent="#ff0000"  → accent + online overridden
+ *   - MobileAccentProvider renders children
+ *   - Never mutates the static MOL_LIGHT/MOL_DARK singletons
+ *
+ * The pure functions (getPalette, normalizeStatus, tierCode) are covered
+ * in palette.test.ts — only the React context/hook is tested here.
+ */
+import { afterEach, describe, expect, it, vi } from "vitest";
+import { cleanup, render } from "@testing-library/react";
+import React from "react";
+
+import { MobileAccentProvider, usePalette } from "../palette-context";
+import { MOL_DARK, MOL_LIGHT } from "../palette";
+
+afterEach(() => {
+  cleanup();
+  vi.restoreAllMocks();
+});
+
+// ─── Test helpers ──────────────────────────────────────────────────────────────
+// Each helper renders exactly one usePalette value as a testid element.
+// Using unique testids per scenario avoids "multiple elements" DOM pollution
+// when tests run in the same jsdom worker without strict cleanup timing.
+
+function AccentDump({ dark }: { dark: boolean }) {
+  const palette = usePalette(dark);
+  return <span data-testid="accent-val">{palette.accent}</span>;
+}
+
+function OnlineDump({ dark }: { dark: boolean }) {
+  const palette = usePalette(dark);
+  return <span data-testid="online-val">{palette.online}</span>;
+}
+
+// ─── MobileAccentProvider ──────────────────────────────────────────────────────
+describe("MobileAccentProvider", () => {
+  it("renders children", () => {
+    const { getByText } = render(
+      <MobileAccentProvider accent={null}>
+        <span>child content</span>
+      </MobileAccentProvider>,
+    );
+    expect(getByText("child content").textContent).toBe("child content");
+  });
+});
+
+// ─── usePalette — no provider ─────────────────────────────────────────────────
+describe("usePalette without MobileAccentProvider", () => {
+  it("returns MOL_LIGHT when dark=false", () => {
+    const { getByTestId } = render(<AccentDump dark={false} />);
+    expect(getByTestId("accent-val").textContent).toBe(MOL_LIGHT.accent);
+  });
+
+  it("returns MOL_DARK when dark=true", () => {
+    const { getByTestId } = render(<AccentDump dark={true} />);
+    expect(getByTestId("accent-val").textContent).toBe(MOL_DARK.accent);
+  });
+});
+
+// ─── usePalette — with MobileAccentProvider ────────────────────────────────────
+describe("usePalette with MobileAccentProvider", () => {
+  it("returns base palette unchanged when accent=null", () => {
+    const { getByTestId } = render(
+      <MobileAccentProvider accent={null}>
+        <AccentDump dark={false} />
+      </MobileAccentProvider>,
+    );
+    expect(getByTestId("accent-val").textContent).toBe(MOL_LIGHT.accent);
+  });
+
+  it("returns base palette unchanged when accent matches base.accent (identity guard)", () => {
+    const { getByTestId } = render(
+      <MobileAccentProvider accent={MOL_LIGHT.accent}>
+        <AccentDump dark={false} />
+      </MobileAccentProvider>,
+    );
+    expect(getByTestId("accent-val").textContent).toBe(MOL_LIGHT.accent);
+  });
+
+  it("overrides accent when provider supplies a different colour", () => {
+    const CUSTOM = "#ff0000";
+    const { getByTestId } = render(
+      <MobileAccentProvider accent={CUSTOM}>
+        <AccentDump dark={false} />
+      </MobileAccentProvider>,
+    );
+    expect(getByTestId("accent-val").textContent).toBe(CUSTOM);
+  });
+
+  it("also overrides online when accent is overridden", () => {
+    const CUSTOM = "#ff8800";
+    const { getByTestId } = render(
+      <MobileAccentProvider accent={CUSTOM}>
+        <OnlineDump dark={false} />
+      </MobileAccentProvider>,
+    );
+    expect(getByTestId("online-val").textContent).toBe(CUSTOM);
+  });
+});
+
+// ─── Immutability ─────────────────────────────────────────────────────────────
+describe("MOL_LIGHT and MOL_DARK singletons are never mutated", () => {
+  it("MOL_LIGHT.accent unchanged after custom-accent render", () => {
+    const before = MOL_LIGHT.accent;
+    render(
+      <MobileAccentProvider accent="#deadbeef">
+        <AccentDump dark={false} />
+      </MobileAccentProvider>,
+    );
+    expect(MOL_LIGHT.accent).toBe(before);
+  });
+
+  it("MOL_DARK.accent unchanged after custom-accent render", () => {
+    const before = MOL_DARK.accent;
+    render(
+      <MobileAccentProvider accent="#bada55ff">
+        <AccentDump dark={true} />
+      </MobileAccentProvider>,
+    );
+    expect(MOL_DARK.accent).toBe(before);
+  });
+});