diff --git a/src/test/proposal-essential.test.tsx b/src/test/proposal-essential.test.tsx
new file mode 100644
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--- /dev/null
+++ b/src/test/proposal-essential.test.tsx
@@ -0,0 +1,553 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest'
+import { render, screen, waitFor, fireEvent, cleanup } from '@testing-library/react'
+import userEvent from '@testing-library/user-event'
+import ProposalDetailPage from '@/pages/ProposalDetailPage'
+import { MemoryRouter, Routes, Route } from 'react-router-dom'
+
+const mockGet = vi.fn()
+const mockPost = vi.fn()
+const mockPatch = vi.fn()
+const mockDelete = vi.fn()
+
+vi.mock('@/services/api', () => ({
+  default: {
+    get: (...args: any[]) => mockGet(...args),
+    post: (...args: any[]) => mockPost(...args),
+    patch: (...args: any[]) => mockPatch(...args),
+    delete: (...args: any[]) => mockDelete(...args),
+  },
+}))
+
+const mockNavigate = vi.fn()
+vi.mock('react-router-dom', async () => {
+  const actual = await vi.importActual('react-router-dom')
+  return {
+    ...actual,
+    useNavigate: () => mockNavigate,
+    useParams: () => ({ id: '1' }),
+    useSearchParams: () => [new URLSearchParams('?project_id=1'), vi.fn()],
+  }
+})
+
+type Essential = {
+  id: number
+  essential_code: string
+  proposal_id: number
+  type: 'feature' | 'improvement' | 'refactor'
+  title: string
+  description: string | null
+  created_by_id: number | null
+  created_at: string
+  updated_at: string | null
+}
+
+type Proposal = {
+  id: number
+  proposal_code: string | null
+  title: string
+  description: string | null
+  status: 'open' | 'accepted' | 'rejected'
+  project_id: number
+  created_by_id: number | null
+  created_by_username: string | null
+  feat_task_id: string | null
+  essentials: Essential[] | null
+  generated_tasks: any[] | null
+  created_at: string
+  updated_at: string | null
+}
+
+type Milestone = {
+  id: number
+  title: string
+  status: 'open' | 'freeze' | 'undergoing' | 'completed' | 'closed'
+}
+
+const mockProposal: Proposal = {
+  id: 1,
+  proposal_code: 'PROP-001',
+  title: 'Test Proposal',
+  description: 'Test description',
+  status: 'open',
+  project_id: 1,
+  created_by_id: 1,
+  created_by_username: 'admin',
+  feat_task_id: null,
+  essentials: [],
+  generated_tasks: null,
+  created_at: '2026-03-01T00:00:00Z',
+  updated_at: null,
+}
+
+const mockEssentials: Essential[] = [
+  {
+    id: 1,
+    essential_code: 'ESS-001',
+    proposal_id: 1,
+    type: 'feature',
+    title: 'Feature Essential',
+    description: 'A feature essential',
+    created_by_id: 1,
+    created_at: '2026-03-01T00:00:00Z',
+    updated_at: null,
+  },
+  {
+    id: 2,
+    essential_code: 'ESS-002',
+    proposal_id: 1,
+    type: 'improvement',
+    title: 'Improvement Essential',
+    description: null,
+    created_by_id: 1,
+    created_at: '2026-03-01T00:00:00Z',
+    updated_at: null,
+  },
+]
+
+const mockMilestones: Milestone[] = [
+  { id: 1, title: 'Milestone 1', status: 'open' },
+  { id: 2, title: 'Milestone 2', status: 'open' },
+]
+
+function setupApi(options?: {
+  proposal?: Proposal
+  essentials?: Essential[]
+  milestones?: Milestone[]
+  error?: string
+}) {
+  const proposal = options?.proposal ?? mockProposal
+  const essentials = options?.essentials ?? mockEssentials
+  const milestones = options?.milestones ?? mockMilestones
+
+  mockGet.mockImplementation((url: string) => {
+    if (url.includes('/proposals/1') && !url.includes('/essentials')) {
+      if (options?.error) {
+        return Promise.reject({ response: { data: { detail: options.error } } })
+      }
+      return Promise.resolve({ data: proposal })
+    }
+    if (url.includes('/essentials')) {
+      return Promise.resolve({ data: essentials })
+    }
+    if (url.includes('/milestones')) {
+      return Promise.resolve({ data: milestones })
+    }
+    return Promise.reject(new Error(`Unhandled GET ${url}`))
+  })
+
+  mockPost.mockResolvedValue({ data: {} })
+  mockPatch.mockResolvedValue({ data: {} })
+  mockDelete.mockResolvedValue({ data: {} })
+}
+
+describe('ProposalDetailPage', () => {
+  beforeEach(() => {
+    vi.clearAllMocks()
+    setupApi()
+    vi.spyOn(window, 'confirm').mockReturnValue(true)
+  })
+
+  afterEach(() => {
+    cleanup()
+    vi.restoreAllMocks()
+  })
+
+  describe('Essential List Display', () => {
+    it('renders essentials section with count', async () => {
+      render(<ProposalDetailPage />)
+
+      await waitFor(() => {
+        expect(screen.getByText('Essentials (2)')).toBeInTheDocument()
+      })
+    })
+
+    it('displays essential cards with type badges', async () => {
+      render(<ProposalDetailPage />)
+
+      await waitFor(() => {
+        expect(screen.getByText('Feature Essential')).toBeInTheDocument()
+      })
+
+      expect(screen.getByText('Improvement Essential')).toBeInTheDocument()
+      expect(screen.getByText('feature')).toBeInTheDocument()
+      expect(screen.getByText('improvement')).toBeInTheDocument()
+    })
+
+    it('displays essential codes', async () => {
+      render(<ProposalDetailPage />)
+
+      await waitFor(() => {
+        expect(screen.getByText('ESS-001')).toBeInTheDocument()
+      })
+
+      expect(screen.getByText('ESS-002')).toBeInTheDocument()
+    })
+
+    it('displays essential descriptions when available', async () => {
+      render(<ProposalDetailPage />)
+
+      await waitFor(() => {
+        expect(screen.getByText('A feature essential')).toBeInTheDocument()
+      })
+    })
+
+    it('shows empty state when no essentials', async () => {
+      setupApi({ essentials: [] })
+      render(<ProposalDetailPage />)
+
+      await waitFor(() => {
+        expect(screen.getByText('Essentials (0)')).toBeInTheDocument()
+      })
+
+      expect(screen.getByText(/No essentials yet/)).toBeInTheDocument()
+      expect(screen.getByText(/Add one to define deliverables/)).toBeInTheDocument()
+    })
+
+    it('shows loading state for essentials', async () => {
+      mockGet.mockImplementation((url: string) => {
+        if (url.includes('/proposals/1') && !url.includes('/essentials')) {
+          return Promise.resolve({ data: mockProposal })
+        }
+        if (url.includes('/essentials')) {
+          return new Promise(() => {}) // Never resolve
+        }
+        return Promise.reject(new Error(`Unhandled GET ${url}`))
+      })
+
+      render(<ProposalDetailPage />)
+
+      await waitFor(() => {
+        expect(screen.getByText(/Loading/i)).toBeInTheDocument()
+      })
+    })
+  })
+
+  describe('Essential Create/Edit Forms', () => {
+    it('opens create essential modal', async () => {
+      render(<ProposalDetailPage />)
+
+      await waitFor(() => {
+        expect(screen.getByText('+ New Essential')).toBeInTheDocument()
+      })
+
+      await userEvent.click(screen.getByText('+ New Essential'))
+
+      expect(screen.getByRole('heading', { name: 'New Essential' })).toBeInTheDocument()
+      expect(screen.getByPlaceholderText('Essential title')).toBeInTheDocument()
+      expect(screen.getByText('Feature')).toBeInTheDocument()
+      expect(screen.getByText('Improvement')).toBeInTheDocument()
+      expect(screen.getByText('Refactor')).toBeInTheDocument()
+    })
+
+    it('creates new essential', async () => {
+      render(<ProposalDetailPage />)
+
+      await waitFor(() => {
+        expect(screen.getByText('+ New Essential')).toBeInTheDocument()
+      })
+
+      await userEvent.click(screen.getByText('+ New Essential'))
+
+      await userEvent.type(screen.getByPlaceholderText('Essential title'), 'New Test Essential')
+      fireEvent.change(screen.getAllByRole('combobox')[0], { target: { value: 'refactor' } })
+      await userEvent.type(screen.getByPlaceholderText('Description (optional)'), 'Test description')
+
+      await userEvent.click(screen.getByRole('button', { name: 'Save' }))
+
+      await waitFor(() => {
+        expect(mockPost).toHaveBeenCalledWith(
+          '/projects/1/proposals/1/essentials',
+          expect.objectContaining({
+            title: 'New Test Essential',
+            type: 'refactor',
+            description: 'Test description',
+          })
+        )
+      })
+    })
+
+    it('opens edit essential modal with pre-filled data', async () => {
+      render(<ProposalDetailPage />)
+
+      await waitFor(() => {
+        expect(screen.getByText('Feature Essential')).toBeInTheDocument()
+      })
+
+      const editButtons = screen.getAllByRole('button', { name: 'Edit' })
+      await userEvent.click(editButtons[0])
+
+      expect(screen.getByRole('heading', { name: 'Edit Essential' })).toBeInTheDocument()
+
+      const titleInput = screen.getByDisplayValue('Feature Essential')
+      expect(titleInput).toBeInTheDocument()
+
+      const descriptionInput = screen.getByDisplayValue('A feature essential')
+      expect(descriptionInput).toBeInTheDocument()
+    })
+
+    it('updates essential', async () => {
+      render(<ProposalDetailPage />)
+
+      await waitFor(() => {
+        expect(screen.getByText('Feature Essential')).toBeInTheDocument()
+      })
+
+      const editButtons = screen.getAllByRole('button', { name: 'Edit' })
+      await userEvent.click(editButtons[0])
+
+      const titleInput = screen.getByDisplayValue('Feature Essential')
+      await userEvent.clear(titleInput)
+      await userEvent.type(titleInput, 'Updated Essential Title')
+
+      await userEvent.click(screen.getByRole('button', { name: 'Save' }))
+
+      await waitFor(() => {
+        expect(mockPatch).toHaveBeenCalledWith(
+          '/projects/1/proposals/1/essentials/1',
+          expect.objectContaining({
+            title: 'Updated Essential Title',
+            type: 'feature',
+            description: 'A feature essential',
+          })
+        )
+      })
+    })
+
+    it('deletes essential after confirmation', async () => {
+      render(<ProposalDetailPage />)
+
+      await waitFor(() => {
+        expect(screen.getByText('Feature Essential')).toBeInTheDocument()
+      })
+
+      const deleteButtons = screen.getAllByRole('button', { name: 'Delete' })
+      await userEvent.click(deleteButtons[0])
+
+      await waitFor(() => {
+        expect(window.confirm).toHaveBeenCalledWith('Are you sure you want to delete this Essential?')
+      })
+
+      await waitFor(() => {
+        expect(mockDelete).toHaveBeenCalledWith('/projects/1/proposals/1/essentials/1')
+      })
+    })
+
+    it('disables save button when title is empty', async () => {
+      render(<ProposalDetailPage />)
+
+      await waitFor(() => {
+        expect(screen.getByText('+ New Essential')).toBeInTheDocument()
+      })
+
+      await userEvent.click(screen.getByText('+ New Essential'))
+
+      const saveButton = screen.getByRole('button', { name: 'Save' })
+      expect(saveButton).toBeDisabled()
+
+      await userEvent.type(screen.getByPlaceholderText('Essential title'), 'Some Title')
+      expect(saveButton).toBeEnabled()
+
+      await userEvent.clear(screen.getByPlaceholderText('Essential title'))
+      expect(saveButton).toBeDisabled()
+    })
+  })
+
+  describe('Accept with Milestone Selection', () => {
+    it('opens accept modal with milestone selector', async () => {
+      render(<ProposalDetailPage />)
+
+      await waitFor(() => {
+        expect(screen.getByText('Accept')).toBeInTheDocument()
+      })
+
+      await userEvent.click(screen.getByText('Accept'))
+
+      expect(screen.getByRole('heading', { name: 'Accept Proposal' })).toBeInTheDocument()
+      expect(screen.getByText(/Select an.*open.*milestone/i)).toBeInTheDocument()
+      expect(screen.getByRole('combobox')).toBeInTheDocument()
+    })
+
+    it('disables confirm button without milestone selection', async () => {
+      render(<ProposalDetailPage />)
+
+      await waitFor(() => {
+        expect(screen.getByText('Accept')).toBeInTheDocument()
+      })
+
+      await userEvent.click(screen.getByText('Accept'))
+
+      const confirmButton = screen.getByRole('button', { name: 'Confirm Accept' })
+      expect(confirmButton).toBeDisabled()
+    })
+
+    it('enables confirm button after milestone selection', async () => {
+      render(<ProposalDetailPage />)
+
+      await waitFor(() => {
+        expect(screen.getByText('Accept')).toBeInTheDocument()
+      })
+
+      await userEvent.click(screen.getByText('Accept'))
+
+      const select = screen.getByRole('combobox')
+      fireEvent.change(select, { target: { value: '1' } })
+
+      const confirmButton = screen.getByRole('button', { name: 'Confirm Accept' })
+      expect(confirmButton).toBeEnabled()
+    })
+
+    it('calls accept API with selected milestone', async () => {
+      render(<ProposalDetailPage />)
+
+      await waitFor(() => {
+        expect(screen.getByText('Accept')).toBeInTheDocument()
+      })
+
+      await userEvent.click(screen.getByText('Accept'))
+
+      const select = screen.getByRole('combobox')
+      fireEvent.change(select, { target: { value: '1' } })
+
+      await userEvent.click(screen.getByRole('button', { name: 'Confirm Accept' }))
+
+      await waitFor(() => {
+        expect(mockPost).toHaveBeenCalledWith(
+          '/projects/1/proposals/1/accept',
+          { milestone_id: 1 }
+        )
+      })
+    })
+
+    it('shows warning when no open milestones available', async () => {
+      setupApi({ milestones: [] })
+      render(<ProposalDetailPage />)
+
+      await waitFor(() => {
+        expect(screen.getByText('Accept')).toBeInTheDocument()
+      })
+
+      await userEvent.click(screen.getByText('Accept'))
+
+      expect(screen.getByText('No open milestones available.')).toBeInTheDocument()
+    })
+
+    it('displays generated tasks after accept', async () => {
+      const acceptedProposal: Proposal = {
+        ...mockProposal,
+        status: 'accepted',
+        generated_tasks: [
+          { task_id: 1, task_code: 'TASK-001', title: 'Story Task 1', task_type: 'story', task_subtype: 'feature' },
+          { task_id: 2, task_code: 'TASK-002', title: 'Story Task 2', task_type: 'story', task_subtype: 'improvement' },
+        ],
+      }
+      setupApi({ proposal: acceptedProposal })
+
+      render(<ProposalDetailPage />)
+
+      await waitFor(() => {
+        expect(screen.getByText('Generated Tasks')).toBeInTheDocument()
+      })
+
+      expect(screen.getByText('Story Task 1')).toBeInTheDocument()
+      expect(screen.getByText('Story Task 2')).toBeInTheDocument()
+      expect(screen.getByText('story/feature')).toBeInTheDocument()
+      expect(screen.getByText('story/improvement')).toBeInTheDocument()
+    })
+  })
+
+  describe('Story Creation Restriction UI', () => {
+    it('hides essential controls for accepted proposal', async () => {
+      const acceptedProposal: Proposal = {
+        ...mockProposal,
+        status: 'accepted',
+        essentials: mockEssentials,
+      }
+      setupApi({ proposal: acceptedProposal })
+
+      render(<ProposalDetailPage />)
+
+      await waitFor(() => {
+        expect(screen.getByText('accepted')).toBeInTheDocument()
+      })
+
+      expect(screen.queryByText('+ New Essential')).not.toBeInTheDocument()
+    })
+
+    it('hides edit/delete buttons for essentials when proposal is accepted', async () => {
+      const acceptedProposal: Proposal = {
+        ...mockProposal,
+        status: 'accepted',
+        essentials: mockEssentials,
+      }
+      setupApi({ proposal: acceptedProposal })
+
+      render(<ProposalDetailPage />)
+
+      await waitFor(() => {
+        expect(screen.getByText('Feature Essential')).toBeInTheDocument()
+      })
+
+      // Edit and Delete buttons should not be visible
+      const editButtons = screen.queryAllByRole('button', { name: 'Edit' })
+      const deleteButtons = screen.queryAllByRole('button', { name: 'Delete' })
+
+      // Only the main proposal Edit button might exist, but not essential edit buttons
+      expect(deleteButtons.length).toBe(0)
+    })
+
+    it('hides edit/delete buttons for rejected proposal', async () => {
+      const rejectedProposal: Proposal = {
+        ...mockProposal,
+        status: 'rejected',
+        essentials: mockEssentials,
+      }
+      setupApi({ proposal: rejectedProposal })
+
+      render(<ProposalDetailPage />)
+
+      await waitFor(() => {
+        expect(screen.getByText('rejected')).toBeInTheDocument()
+      })
+
+      expect(screen.queryByText('+ New Essential')).not.toBeInTheDocument()
+    })
+  })
+
+  describe('Error Handling', () => {
+    it('displays error message on essential create failure', async () => {
+      mockPost.mockRejectedValue({ response: { data: { detail: 'Failed to create essential' } } })
+
+      render(<ProposalDetailPage />)
+
+      await waitFor(() => {
+        expect(screen.getByText('+ New Essential')).toBeInTheDocument()
+      })
+
+      await userEvent.click(screen.getByText('+ New Essential'))
+      await userEvent.type(screen.getByPlaceholderText('Essential title'), 'Test')
+      await userEvent.click(screen.getByRole('button', { name: 'Save' }))
+
+      await waitFor(() => {
+        expect(screen.getByText('Failed to create essential')).toBeInTheDocument()
+      })
+    })
+
+    it('displays error message on accept failure', async () => {
+      mockPost.mockRejectedValue({ response: { data: { detail: 'Accept failed: milestone required' } } })
+
+      render(<ProposalDetailPage />)
+
+      await waitFor(() => {
+        expect(screen.getByText('Accept')).toBeInTheDocument()
+      })
+
+      await userEvent.click(screen.getByText('Accept'))
+      fireEvent.change(screen.getByRole('combobox'), { target: { value: '1' } })
+      await userEvent.click(screen.getByRole('button', { name: 'Confirm Accept' }))
+
+      await waitFor(() => {
+        expect(screen.getByText('Accept failed: milestone required')).toBeInTheDocument()
+      })
+    })
+  })
+})