diff --git a/src/auth/AuthProvider.test.tsx b/src/auth/AuthProvider.test.tsx
new file mode 100644
index 0000000..78c386d
--- /dev/null
+++ b/src/auth/AuthProvider.test.tsx
@@ -0,0 +1,78 @@
+// @vitest-environment happy-dom
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import { renderHook, act, waitFor } from "@testing-library/react";
+
+vi.mock("./api", () => ({
+  authApi: {
+    me: vi.fn(),
+    login: vi.fn(),
+    logout: vi.fn(),
+  },
+}));
+
+import { authApi } from "./api";
+import { AuthProvider, useAuth } from "./AuthProvider";
+
+const wrapper = ({ children }: { children: React.ReactNode }) => (
+  <AuthProvider>{children}</AuthProvider>
+);
+
+describe("AuthProvider", () => {
+  beforeEach(() => {
+    vi.resetAllMocks();
+  });
+
+  it("loads user on mount", async () => {
+    (authApi.me as unknown as ReturnType<typeof vi.fn>).mockResolvedValue({
+      id: 1,
+      username: "alice",
+      role: "user",
+    });
+    const { result } = renderHook(() => useAuth(), { wrapper });
+    await waitFor(() => expect(result.current.status).toBe("authenticated"));
+    expect(result.current.user?.username).toBe("alice");
+  });
+
+  it("status is unauthenticated when /me fails", async () => {
+    (authApi.me as unknown as ReturnType<typeof vi.fn>).mockRejectedValue(
+      new Error("401")
+    );
+    const { result } = renderHook(() => useAuth(), { wrapper });
+    await waitFor(() => expect(result.current.status).toBe("unauthenticated"));
+    expect(result.current.user).toBeNull();
+  });
+
+  it("login() updates state on success", async () => {
+    (authApi.me as unknown as ReturnType<typeof vi.fn>).mockRejectedValue(
+      new Error("401")
+    );
+    (
+      authApi.login as unknown as ReturnType<typeof vi.fn>
+    ).mockResolvedValue({ id: 1, username: "alice", role: "admin" });
+    const { result } = renderHook(() => useAuth(), { wrapper });
+    await waitFor(() => expect(result.current.status).toBe("unauthenticated"));
+    await act(async () => {
+      await result.current.login("alice", "pw");
+    });
+    expect(result.current.user?.username).toBe("alice");
+    expect(result.current.status).toBe("authenticated");
+  });
+
+  it("logout() clears state", async () => {
+    (authApi.me as unknown as ReturnType<typeof vi.fn>).mockResolvedValue({
+      id: 1,
+      username: "alice",
+      role: "user",
+    });
+    (
+      authApi.logout as unknown as ReturnType<typeof vi.fn>
+    ).mockResolvedValue(undefined);
+    const { result } = renderHook(() => useAuth(), { wrapper });
+    await waitFor(() => expect(result.current.status).toBe("authenticated"));
+    await act(async () => {
+      await result.current.logout();
+    });
+    expect(result.current.user).toBeNull();
+    expect(result.current.status).toBe("unauthenticated");
+  });
+});
diff --git a/src/auth/AuthProvider.tsx b/src/auth/AuthProvider.tsx
new file mode 100644
index 0000000..f51f46e
--- /dev/null
+++ b/src/auth/AuthProvider.tsx
@@ -0,0 +1,58 @@
+import { useEffect, useState, useCallback, type ReactNode } from "react";
+import { AuthContext, type AuthContextValue, type AuthStatus } from "./useAuth";
+import { authApi } from "./api";
+import type { User } from "@/types";
+
+// Re-export useAuth so consumers can import both the context provider and
+// the hook from the same module. The hook itself lives in `./useAuth` so
+// the type definitions stay tree-shakeable independent of the provider.
+export { useAuth } from "./useAuth";
+
+/**
+ * Wraps the app and exposes the auth context. On mount it probes
+ * /api/auth/me to decide whether the existing `cyclone_session`
+ * cookie is still valid. Callers (route guard, sidebar, RoleGate,
+ * Login page) read the resulting `status` + `user` via `useAuth()`.
+ *
+ *   - "loading"        → while the probe is in flight
+ *   - "authenticated"  → probe succeeded; user populated
+ *   - "unauthenticated"→ probe failed; user is null
+ *
+ * `login` and `logout` mutate local state directly so the UI flips
+ * without waiting for a second /me round-trip.
+ */
+export function AuthProvider({ children }: { children: ReactNode }) {
+  const [status, setStatus] = useState<AuthStatus>("loading");
+  const [user, setUser] = useState<User | null>(null);
+
+  const refresh = useCallback(async () => {
+    setStatus("loading");
+    try {
+      const me = await authApi.me();
+      setUser(me as User);
+      setStatus("authenticated");
+    } catch {
+      setUser(null);
+      setStatus("unauthenticated");
+    }
+  }, []);
+
+  useEffect(() => {
+    void refresh();
+  }, [refresh]);
+
+  const login = useCallback(async (username: string, password: string) => {
+    const u = await authApi.login(username, password);
+    setUser(u as User);
+    setStatus("authenticated");
+  }, []);
+
+  const logout = useCallback(async () => {
+    await authApi.logout().catch(() => undefined);
+    setUser(null);
+    setStatus("unauthenticated");
+  }, []);
+
+  const value: AuthContextValue = { status, user, login, logout, refresh };
+  return <AuthContext.Provider value={value}>{children}</AuthContext.Provider>;
+}
diff --git a/src/auth/useAuth.ts b/src/auth/useAuth.ts
new file mode 100644
index 0000000..aee1c54
--- /dev/null
+++ b/src/auth/useAuth.ts
@@ -0,0 +1,56 @@
+import { createContext, useContext } from "react";
+import type { User } from "@/types";
+
+/**
+ * Tri-state lifecycle for the auth surface.
+ *
+ *   - "loading"        → we haven't asked /api/auth/me yet, or the result
+ *                         is still in flight. Route guards render a
+ *                         placeholder so we don't bounce the user to
+ *                         /login before the cookie has had a chance to
+ *                         prove itself.
+ *   - "authenticated"  → /me returned a real User. The rest of the app
+ *                         can safely render protected surfaces.
+ *   - "unauthenticated"→ /me failed (no cookie, expired cookie, server
+ *                         down). Route guards redirect to /login.
+ */
+export type AuthStatus = "loading" | "authenticated" | "unauthenticated";
+
+export interface AuthContextValue {
+  status: AuthStatus;
+  user: User | null;
+  /**
+   * Authenticate against /api/auth/login. Throws `ApiError` on failure
+   * (with `code` = "invalid_credentials" | "account_disabled" |
+   * "rate_limited" | "error"). On success, status flips to
+   * "authenticated" and `user` is populated.
+   */
+  login: (username: string, password: string) => Promise<void>;
+  /**
+   * Hit /api/auth/logout and clear local state. Always succeeds
+   * locally — even if the server is unreachable, the operator is
+   * effectively signed out from the SPA's perspective.
+   */
+  logout: () => Promise<void>;
+  /**
+   * Re-run the /api/auth/me probe. Useful after a profile edit on the
+   * admin pages so the sidebar reflects the new role without a
+   * full reload.
+   */
+  refresh: () => Promise<void>;
+}
+
+export const AuthContext = createContext<AuthContextValue | null>(null);
+
+/**
+ * Read the current auth context. Throws when used outside of an
+ * `<AuthProvider>` so consumers fail loudly during development instead
+ * of silently rendering the unauthenticated branch.
+ */
+export function useAuth(): AuthContextValue {
+  const ctx = useContext(AuthContext);
+  if (!ctx) {
+    throw new Error("useAuth must be used inside <AuthProvider>");
+  }
+  return ctx;
+}