diff --git a/frontend/cntr/ErrorBoundary/ErrorBoundary.test.tsx b/frontend/cntr/ErrorBoundary/ErrorBoundary.test.tsx
new file mode 100644
index 0000000..44f7831
--- /dev/null
+++ b/frontend/cntr/ErrorBoundary/ErrorBoundary.test.tsx
@@ -0,0 +1,33 @@
+import { render, screen, fireEvent } from '@testing-library/react';
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+import { ErrorBoundary } from './ErrorBoundary';
+
+const Bomb = ({ shouldThrow }: { shouldThrow: boolean }) => {
+  if (shouldThrow) throw new Error('Test error');
+  return <div>OK</div>;
+};
+
+beforeEach(() => { vi.spyOn(console, 'error').mockImplementation(() => {}); });
+
+describe('ErrorBoundary', () => {
+  it('renders children when no error', () => {
+    render(<ErrorBoundary><Bomb shouldThrow={false} /></ErrorBoundary>);
+    expect(screen.getByText('OK')).toBeInTheDocument();
+  });
+
+  it('renders default fallback UI on error', () => {
+    render(<ErrorBoundary><Bomb shouldThrow={true} /></ErrorBoundary>);
+    expect(screen.getByText(/something went wrong/i)).toBeInTheDocument();
+  });
+
+  it('renders custom fallback when provided', () => {
+    render(<ErrorBoundary fallback={<div>Custom error</div>}><Bomb shouldThrow={true} /></ErrorBoundary>);
+    expect(screen.getByText('Custom error')).toBeInTheDocument();
+  });
+
+  it('resets on Try again click', () => {
+    render(<ErrorBoundary><Bomb shouldThrow={true} /></ErrorBoundary>);
+    fireEvent.click(screen.getByRole('button', { name: /try again/i }));
+    expect(screen.queryByText(/something went wrong/i)).not.toBeInTheDocument();
+  });
+});
\ No newline at end of file
diff --git a/frontend/cntr/ErrorBoundary/ErrorBoundary.tsx b/frontend/cntr/ErrorBoundary/ErrorBoundary.tsx
new file mode 100644
index 0000000..d8c7841
--- /dev/null
+++ b/frontend/cntr/ErrorBoundary/ErrorBoundary.tsx
@@ -0,0 +1,43 @@
+import React from 'react';
+
+interface Props {
+  children: React.ReactNode;
+  fallback?: React.ReactNode;
+}
+
+interface State {
+  hasError: boolean;
+}
+
+export class ErrorBoundary extends React.Component<Props, State> {
+  state: State = { hasError: false };
+
+  static getDerivedStateFromError(): State {
+    return { hasError: true };
+  }
+
+  componentDidCatch(error: Error, info: React.ErrorInfo): void {
+    console.error('[ErrorBoundary]', error, info);
+  }
+
+  reset = () => this.setState({ hasError: false });
+
+  render() {
+    if (this.state.hasError) {
+      if (this.props.fallback) return this.props.fallback;
+      return (
+        <div className="flex flex-col items-center justify-center py-16 text-center px-4">
+          <p className="text-lg font-semibold text-gray-700 mb-2">Something went wrong</p>
+          <p className="text-sm text-gray-500 mb-4">An unexpected error occurred. Please try again.</p>
+          <button
+            onClick={this.reset}
+            className="px-4 py-2 bg-blue-600 text-white text-sm rounded hover:bg-blue-700"
+          >
+            Try again
+          </button>
+        </div>
+      );
+    }
+    return this.props.children;
+  }
+}
\ No newline at end of file
diff --git a/frontend/cntr/PasswordStrengthMeter/PasswordStrengthMeter.test.tsx b/frontend/cntr/PasswordStrengthMeter/PasswordStrengthMeter.test.tsx
new file mode 100644
index 0000000..e29e70a
--- /dev/null
+++ b/frontend/cntr/PasswordStrengthMeter/PasswordStrengthMeter.test.tsx
@@ -0,0 +1,30 @@
+import { render, screen } from '@testing-library/react';
+import { describe, it, expect } from 'vitest';
+import { PasswordStrengthMeter } from './PasswordStrengthMeter';
+
+describe('PasswordStrengthMeter', () => {
+  it('renders nothing for empty password', () => {
+    const { container } = render(<PasswordStrengthMeter password="" />);
+    expect(container.firstChild).toBeNull();
+  });
+
+  it('shows Weak for short simple password', () => {
+    render(<PasswordStrengthMeter password="abc" />);
+    expect(screen.getByText('Weak')).toBeInTheDocument();
+  });
+
+  it('shows Fair for moderate password', () => {
+    render(<PasswordStrengthMeter password="abcABC12" />);
+    expect(screen.getByText(/fair|good|strong/i)).toBeInTheDocument();
+  });
+
+  it('shows Strong for complex password', () => {
+    render(<PasswordStrengthMeter password="Abcdef1!" />);
+    expect(screen.getByText('Strong')).toBeInTheDocument();
+  });
+
+  it('renders 4 segments', () => {
+    const { container } = render(<PasswordStrengthMeter password="Test1!" />);
+    expect(container.querySelectorAll('.flex-1').length).toBe(4);
+  });
+});
\ No newline at end of file
diff --git a/frontend/cntr/PasswordStrengthMeter/PasswordStrengthMeter.tsx b/frontend/cntr/PasswordStrengthMeter/PasswordStrengthMeter.tsx
new file mode 100644
index 0000000..c058637
--- /dev/null
+++ b/frontend/cntr/PasswordStrengthMeter/PasswordStrengthMeter.tsx
@@ -0,0 +1,43 @@
+import React from 'react';
+
+interface Props { password: string; }
+
+const LEVELS = [
+  { label: 'Weak',   colour: 'bg-red-500' },
+  { label: 'Fair',   colour: 'bg-orange-400' },
+  { label: 'Good',   colour: 'bg-yellow-400' },
+  { label: 'Strong', colour: 'bg-green-500' },
+];
+
+function getScore(password: string): number {
+  let score = 0;
+  if (password.length >= 8)          score++;
+  if (/[A-Z]/.test(password))        score++;
+  if (/[a-z]/.test(password))        score++;
+  if (/[0-9]/.test(password))        score++;
+  if (/[^A-Za-z0-9]/.test(password)) score++;
+  if (score <= 1) return 0;
+  if (score === 2) return 1;
+  if (score === 3) return 2;
+  return 3;
+}
+
+export const PasswordStrengthMeter: React.FC<Props> = ({ password }) => {
+  if (!password) return null;
+  const level = getScore(password);
+  const { label, colour } = LEVELS[level];
+
+  return (
+    <div className="space-y-1">
+      <div className="flex gap-1">
+        {LEVELS.map((l, i) => (
+          <div
+            key={l.label}
+            className={`h-1.5 flex-1 rounded ${i <= level ? colour : 'bg-gray-200'}`}
+          />
+        ))}
+      </div>
+      <p className="text-xs text-gray-600">{label}</p>
+    </div>
+  );
+};
\ No newline at end of file
diff --git a/frontend/cntr/SessionTimeoutModal/SessionTimeoutModal.test.tsx b/frontend/cntr/SessionTimeoutModal/SessionTimeoutModal.test.tsx
new file mode 100644
index 0000000..3aa2302
--- /dev/null
+++ b/frontend/cntr/SessionTimeoutModal/SessionTimeoutModal.test.tsx
@@ -0,0 +1,50 @@
+import { render, screen, act } from '@testing-library/react';
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
+import { SessionTimeoutModal } from './SessionTimeoutModal';
+
+beforeEach(() => { vi.useFakeTimers(); });
+afterEach(() => { vi.useRealTimers(); });
+
+describe('SessionTimeoutModal', () => {
+  it('does not render when expiresAt is null', () => {
+    render(<SessionTimeoutModal expiresAt={null} onExtend={vi.fn()} onSignOut={vi.fn()} />);
+    expect(screen.queryByRole('dialog')).not.toBeInTheDocument();
+  });
+
+  it('does not render when more than 5 minutes remain', () => {
+    const expiresAt = Date.now() + 10 * 60 * 1000;
+    render(<SessionTimeoutModal expiresAt={expiresAt} onExtend={vi.fn()} onSignOut={vi.fn()} />);
+    expect(screen.queryByRole('dialog')).not.toBeInTheDocument();
+  });
+
+  it('renders modal when ≤ 5 minutes remain', () => {
+    const expiresAt = Date.now() + 3 * 60 * 1000;
+    render(<SessionTimeoutModal expiresAt={expiresAt} onExtend={vi.fn()} onSignOut={vi.fn()} />);
+    expect(screen.getByRole('dialog')).toBeInTheDocument();
+  });
+
+  it('calls onExtend when Stay signed in clicked', () => {
+    const onExtend = vi.fn();
+    const expiresAt = Date.now() + 2 * 60 * 1000;
+    render(<SessionTimeoutModal expiresAt={expiresAt} onExtend={onExtend} onSignOut={vi.fn()} />);
+    screen.getByText('Stay signed in').click();
+    expect(onExtend).toHaveBeenCalledTimes(1);
+  });
+
+  it('calls onSignOut when Sign out clicked', () => {
+    const onSignOut = vi.fn();
+    const expiresAt = Date.now() + 2 * 60 * 1000;
+    render(<SessionTimeoutModal expiresAt={expiresAt} onExtend={vi.fn()} onSignOut={onSignOut} />);
+    screen.getByText('Sign out').click();
+    expect(onSignOut).toHaveBeenCalledTimes(1);
+  });
+
+  it('countdown decrements every second', () => {
+    const expiresAt = Date.now() + 2 * 60 * 1000; // 2 min
+    render(<SessionTimeoutModal expiresAt={expiresAt} onExtend={vi.fn()} onSignOut={vi.fn()} />);
+    const before = screen.getByText(/^\d+:\d+$/).textContent;
+    act(() => { vi.advanceTimersByTime(1000); });
+    const after = screen.getByText(/^\d+:\d+$/).textContent;
+    expect(before).not.toBe(after);
+  });
+});
\ No newline at end of file
diff --git a/frontend/cntr/SessionTimeoutModal/SessionTimeoutModal.tsx b/frontend/cntr/SessionTimeoutModal/SessionTimeoutModal.tsx
new file mode 100644
index 0000000..cff8d21
--- /dev/null
+++ b/frontend/cntr/SessionTimeoutModal/SessionTimeoutModal.tsx
@@ -0,0 +1,36 @@
+import React from 'react';
+import { useSessionTimer } from './useSessionTimer';
+
+interface Props {
+  expiresAt: number | null;
+  onExtend: () => void;
+  onSignOut: () => void;
+}
+
+export const SessionTimeoutModal: React.FC<Props> = ({ expiresAt, onExtend, onSignOut }) => {
+  const { secondsLeft, showWarning } = useSessionTimer(expiresAt);
+
+  if (!showWarning) return null;
+
+  const mins = Math.floor(secondsLeft / 60);
+  const secs = secondsLeft % 60;
+  const display = `${mins}:${String(secs).padStart(2, '0')}`;
+
+  return (
+    <div role="dialog" aria-modal="true" aria-label="Session timeout warning" className="fixed inset-0 z-50 flex items-center justify-center bg-black/50">
+      <div className="bg-white rounded-lg shadow-xl p-6 w-80 text-center space-y-4">
+        <h2 className="text-lg font-semibold text-gray-800">Session expiring soon</h2>
+        <p className="text-sm text-gray-600">Your session will expire in</p>
+        <p className="text-3xl font-mono font-bold text-red-600" aria-live="polite">{display}</p>
+        <div className="flex gap-3 justify-center">
+          <button onClick={onExtend} className="px-4 py-2 bg-blue-600 text-white text-sm rounded hover:bg-blue-700">
+            Stay signed in
+          </button>
+          <button onClick={onSignOut} className="px-4 py-2 border border-gray-300 text-sm rounded hover:bg-gray-50">
+            Sign out
+          </button>
+        </div>
+      </div>
+    </div>
+  );
+};
\ No newline at end of file
diff --git a/frontend/cntr/SessionTimeoutModal/useSessionTimer.ts b/frontend/cntr/SessionTimeoutModal/useSessionTimer.ts
new file mode 100644
index 0000000..72c004c
--- /dev/null
+++ b/frontend/cntr/SessionTimeoutModal/useSessionTimer.ts
@@ -0,0 +1,22 @@
+import { useEffect, useState } from 'react';
+
+const WARN_BEFORE_SECONDS = 5 * 60; // 5 minutes
+
+export function useSessionTimer(expiresAt: number | null): { secondsLeft: number; showWarning: boolean } {
+  const [secondsLeft, setSecondsLeft] = useState(0);
+
+  useEffect(() => {
+    if (!expiresAt) return;
+
+    const tick = () => {
+      const remaining = Math.max(0, Math.floor((expiresAt - Date.now()) / 1000));
+      setSecondsLeft(remaining);
+    };
+
+    tick();
+    const id = setInterval(tick, 1000);
+    return () => clearInterval(id);
+  }, [expiresAt]);
+
+  return { secondsLeft, showWarning: secondsLeft > 0 && secondsLeft <= WARN_BEFORE_SECONDS };
+}
\ No newline at end of file
diff --git a/frontend/cntr/Skeletons/InvoiceRowSkeleton.tsx b/frontend/cntr/Skeletons/InvoiceRowSkeleton.tsx
new file mode 100644
index 0000000..fbb0d35
--- /dev/null
+++ b/frontend/cntr/Skeletons/InvoiceRowSkeleton.tsx
@@ -0,0 +1,9 @@
+import React from 'react';
+export const InvoiceRowSkeleton: React.FC = () => (
+  <div className="animate-pulse flex items-center gap-4 px-4 py-3 border-b border-gray-100">
+    <div className="h-4 bg-gray-200 rounded w-24" />
+    <div className="h-4 bg-gray-200 rounded w-32 flex-1" />
+    <div className="h-4 bg-gray-200 rounded w-20" />
+    <div className="h-6 bg-gray-200 rounded w-16" />
+  </div>
+);
\ No newline at end of file
diff --git a/frontend/cntr/Skeletons/MemberRowSkeleton.tsx b/frontend/cntr/Skeletons/MemberRowSkeleton.tsx
new file mode 100644
index 0000000..e9962e9
--- /dev/null
+++ b/frontend/cntr/Skeletons/MemberRowSkeleton.tsx
@@ -0,0 +1,11 @@
+import React from 'react';
+export const MemberRowSkeleton: React.FC = () => (
+  <div className="animate-pulse flex items-center gap-4 px-4 py-3 border-b border-gray-100">
+    <div className="h-9 w-9 bg-gray-200 rounded-full shrink-0" />
+    <div className="flex-1 space-y-1.5">
+      <div className="h-4 bg-gray-200 rounded w-40" />
+      <div className="h-3 bg-gray-200 rounded w-56" />
+    </div>
+    <div className="h-6 bg-gray-200 rounded w-20" />
+  </div>
+);
\ No newline at end of file
diff --git a/frontend/cntr/Skeletons/Skeletons.test.tsx b/frontend/cntr/Skeletons/Skeletons.test.tsx
new file mode 100644
index 0000000..5cc9954
--- /dev/null
+++ b/frontend/cntr/Skeletons/Skeletons.test.tsx
@@ -0,0 +1,30 @@
+import { render } from '@testing-library/react';
+import { describe, it, expect } from 'vitest';
+import { WorkspaceCardSkeleton } from './WorkspaceCardSkeleton';
+import { InvoiceRowSkeleton } from './InvoiceRowSkeleton';
+import { MemberRowSkeleton } from './MemberRowSkeleton';
+import { TableRowSkeleton } from './TableRowSkeleton';
+
+describe('Skeleton components', () => {
+  it('WorkspaceCardSkeleton renders with animate-pulse', () => {
+    const { container } = render(<WorkspaceCardSkeleton />);
+    expect(container.firstChild).toHaveClass('animate-pulse');
+  });
+  it('InvoiceRowSkeleton renders with animate-pulse', () => {
+    const { container } = render(<InvoiceRowSkeleton />);
+    expect(container.firstChild).toHaveClass('animate-pulse');
+  });
+  it('MemberRowSkeleton renders with animate-pulse', () => {
+    const { container } = render(<MemberRowSkeleton />);
+    expect(container.firstChild).toHaveClass('animate-pulse');
+  });
+  it('TableRowSkeleton renders default 4 columns', () => {
+    const { container } = render(<TableRowSkeleton />);
+    expect(container.firstChild).toHaveClass('animate-pulse');
+    expect(container.querySelectorAll('.flex-1').length).toBe(4);
+  });
+  it('TableRowSkeleton renders custom column count', () => {
+    const { container } = render(<TableRowSkeleton cols={6} />);
+    expect(container.querySelectorAll('.flex-1').length).toBe(6);
+  });
+});
\ No newline at end of file
diff --git a/frontend/cntr/Skeletons/TableRowSkeleton.tsx b/frontend/cntr/Skeletons/TableRowSkeleton.tsx
new file mode 100644
index 0000000..f41869d
--- /dev/null
+++ b/frontend/cntr/Skeletons/TableRowSkeleton.tsx
@@ -0,0 +1,9 @@
+import React from 'react';
+interface Props { cols?: number; }
+export const TableRowSkeleton: React.FC<Props> = ({ cols = 4 }) => (
+  <div className="animate-pulse flex items-center gap-4 px-4 py-3 border-b border-gray-100">
+    {Array.from({ length: cols }).map((_, i) => (
+      <div key={i} className="h-4 bg-gray-200 rounded flex-1" />
+    ))}
+  </div>
+);
\ No newline at end of file
diff --git a/frontend/cntr/Skeletons/WorkspaceCardSkeleton.tsx b/frontend/cntr/Skeletons/WorkspaceCardSkeleton.tsx
new file mode 100644
index 0000000..fd48618
--- /dev/null
+++ b/frontend/cntr/Skeletons/WorkspaceCardSkeleton.tsx
@@ -0,0 +1,12 @@
+import React from 'react';
+export const WorkspaceCardSkeleton: React.FC = () => (
+  <div className="animate-pulse rounded-lg border border-gray-200 p-4 space-y-3">
+    <div className="h-32 bg-gray-200 rounded" />
+    <div className="h-4 bg-gray-200 rounded w-3/4" />
+    <div className="h-3 bg-gray-200 rounded w-1/2" />
+    <div className="flex gap-2">
+      <div className="h-6 bg-gray-200 rounded w-16" />
+      <div className="h-6 bg-gray-200 rounded w-16" />
+    </div>
+  </div>
+);
\ No newline at end of file