Fix task and shift self-assignment features

backend/WorkClub.Api/Endpoints/Shifts/ShiftEndpoints.cs

@@ -42,20 +42,24 @@ public static class ShiftEndpoints
 
     private static async Task<Ok<ShiftListDto>> GetShifts(
         ShiftService shiftService,
+        HttpContext httpContext,
         [FromQuery] DateTimeOffset? from = null,
         [FromQuery] DateTimeOffset? to = null,
         [FromQuery] int page = 1,
         [FromQuery] int pageSize = 20)
     {
-        var result = await shiftService.GetShiftsAsync(from, to, page, pageSize);
+        var externalUserId = httpContext.User.FindFirst("sub")?.Value;
+        var result = await shiftService.GetShiftsAsync(from, to, page, pageSize, externalUserId);
         return TypedResults.Ok(result);
     }
 
     private static async Task<Results<Ok<ShiftDetailDto>, NotFound>> GetShift(
         Guid id,
-        ShiftService shiftService)
+        ShiftService shiftService,
+        HttpContext httpContext)
     {
-        var result = await shiftService.GetShiftByIdAsync(id);
+        var externalUserId = httpContext.User.FindFirst("sub")?.Value;
+        var result = await shiftService.GetShiftByIdAsync(id, externalUserId);
 
         if (result == null)
             return TypedResults.NotFound();
@@ -85,9 +89,11 @@ public static class ShiftEndpoints
     private static async Task<Results<Ok<ShiftDetailDto>, NotFound, Conflict<string>>> UpdateShift(
         Guid id,
         UpdateShiftRequest request,
-        ShiftService shiftService)
+        ShiftService shiftService,
+        HttpContext httpContext)
     {
-        var (shift, error, isConflict) = await shiftService.UpdateShiftAsync(id, request);
+        var externalUserId = httpContext.User.FindFirst("sub")?.Value;
+        var (shift, error, isConflict) = await shiftService.UpdateShiftAsync(id, request, externalUserId);
 
         if (error != null)
         {

backend/WorkClub.Api/Endpoints/Tasks/TaskEndpoints.cs

@@ -30,23 +30,35 @@ public static class TaskEndpoints
         group.MapDelete("{id:guid}", DeleteTask)
             .RequireAuthorization("RequireAdmin")
             .WithName("DeleteTask");
+
+        group.MapPost("{id:guid}/assign", AssignTaskToMe)
+            .RequireAuthorization("RequireMember")
+            .WithName("AssignTaskToMe");
+
+        group.MapDelete("{id:guid}/assign", UnassignTaskFromMe)
+            .RequireAuthorization("RequireMember")
+            .WithName("UnassignTaskFromMe");
     }
 
     private static async Task<Ok<TaskListDto>> GetTasks(
         TaskService taskService,
+        HttpContext httpContext,
         [FromQuery] string? status = null,
         [FromQuery] int page = 1,
         [FromQuery] int pageSize = 20)
     {
-        var result = await taskService.GetTasksAsync(status, page, pageSize);
+        var externalUserId = httpContext.User.FindFirst("sub")?.Value;
+        var result = await taskService.GetTasksAsync(status, page, pageSize, externalUserId);
         return TypedResults.Ok(result);
     }
 
     private static async Task<Results<Ok<TaskDetailDto>, NotFound>> GetTask(
         Guid id,
-        TaskService taskService)
+        TaskService taskService,
+        HttpContext httpContext)
     {
-        var result = await taskService.GetTaskByIdAsync(id);
+        var externalUserId = httpContext.User.FindFirst("sub")?.Value;
+        var result = await taskService.GetTaskByIdAsync(id, externalUserId);
 
         if (result == null)
             return TypedResults.NotFound();
@@ -76,9 +88,11 @@ public static class TaskEndpoints
     private static async Task<Results<Ok<TaskDetailDto>, NotFound, UnprocessableEntity<string>, Conflict<string>>> UpdateTask(
         Guid id,
         UpdateTaskRequest request,
-        TaskService taskService)
+        TaskService taskService,
+        HttpContext httpContext)
     {
-        var (task, error, isConflict) = await taskService.UpdateTaskAsync(id, request);
+        var externalUserId = httpContext.User.FindFirst("sub")?.Value;
+        var (task, error, isConflict) = await taskService.UpdateTaskAsync(id, request, externalUserId);
 
         if (error != null)
         {
@@ -105,4 +119,42 @@ public static class TaskEndpoints
 
         return TypedResults.NoContent();
     }
+
+    private static async Task<Results<Ok, BadRequest<string>, NotFound>> AssignTaskToMe(
+        Guid id,
+        TaskService taskService,
+        HttpContext httpContext)
+    {
+        var externalUserId = httpContext.User.FindFirst("sub")?.Value;
+        if (externalUserId == null) return TypedResults.BadRequest("Invalid user");
+
+        var (success, error) = await taskService.AssignToMeAsync(id, externalUserId);
+
+        if (!success)
+        {
+            if (error == "Task not found") return TypedResults.NotFound();
+            return TypedResults.BadRequest(error ?? "Failed to assign task");
+        }
+
+        return TypedResults.Ok();
+    }
+
+    private static async Task<Results<Ok, BadRequest<string>, NotFound>> UnassignTaskFromMe(
+        Guid id,
+        TaskService taskService,
+        HttpContext httpContext)
+    {
+        var externalUserId = httpContext.User.FindFirst("sub")?.Value;
+        if (externalUserId == null) return TypedResults.BadRequest("Invalid user");
+
+        var (success, error) = await taskService.UnassignFromMeAsync(id, externalUserId);
+
+        if (!success)
+        {
+            if (error == "Task not found") return TypedResults.NotFound();
+            return TypedResults.BadRequest(error ?? "Failed to unassign task");
+        }
+
+        return TypedResults.Ok();
+    }
 }

backend/WorkClub.Api/Services/ShiftService.cs

@@ -17,7 +17,7 @@ public class ShiftService
         _tenantProvider = tenantProvider;
     }
 
-    public async Task<ShiftListDto> GetShiftsAsync(DateTimeOffset? from, DateTimeOffset? to, int page, int pageSize)
+    public async Task<ShiftListDto> GetShiftsAsync(DateTimeOffset? from, DateTimeOffset? to, int page, int pageSize, string? currentExternalUserId = null)
     {
         var query = _context.Shifts.AsQueryable();
 
@@ -42,19 +42,37 @@ public class ShiftService
             .Select(g => new { ShiftId = g.Key, Count = g.Count() })
             .ToDictionaryAsync(x => x.ShiftId, x => x.Count);
 
+        var tenantId = _tenantProvider.GetTenantId();
+        var memberId = currentExternalUserId != null 
+            ? await _context.Members
+                .Where(m => m.ExternalUserId == currentExternalUserId && m.TenantId == tenantId)
+                .Select(m => (Guid?)m.Id)
+                .FirstOrDefaultAsync()
+            : null;
+
+        var userSignups = memberId.HasValue
+            ? await _context.ShiftSignups
+                .Where(ss => shiftIds.Contains(ss.ShiftId) && ss.MemberId == memberId.Value)
+                .Select(ss => ss.ShiftId)
+                .ToListAsync()
+            : new List<Guid>();
+            
+        var userSignedUpShiftIds = userSignups.ToHashSet();
+
         var items = shifts.Select(s => new ShiftListItemDto(
             s.Id,
             s.Title,
             s.StartTime,
             s.EndTime,
             s.Capacity,
-            signupCounts.GetValueOrDefault(s.Id, 0)
+            signupCounts.GetValueOrDefault(s.Id, 0),
+            userSignedUpShiftIds.Contains(s.Id)
         )).ToList();
 
         return new ShiftListDto(items, total, page, pageSize);
     }
 
-    public async Task<ShiftDetailDto?> GetShiftByIdAsync(Guid id)
+    public async Task<ShiftDetailDto?> GetShiftByIdAsync(Guid id, string? currentExternalUserId = null)
     {
         var shift = await _context.Shifts.FindAsync(id);
 
@@ -75,6 +93,8 @@ public class ShiftService
             ss.SignedUpAt
         )).ToList();
 
+        var isSignedUp = currentExternalUserId != null && signupDtos.Any(s => s.ExternalUserId == currentExternalUserId);
+
         return new ShiftDetailDto(
             shift.Id,
             shift.Title,
@@ -87,7 +107,8 @@ public class ShiftService
             shift.ClubId,
             shift.CreatedById,
             shift.CreatedAt,
-            shift.UpdatedAt
+            shift.UpdatedAt,
+            isSignedUp
         );
     }
 
@@ -126,13 +147,14 @@ public class ShiftService
             shift.ClubId,
             shift.CreatedById,
             shift.CreatedAt,
-            shift.UpdatedAt
+            shift.UpdatedAt,
+            false
         );
 
         return (dto, null);
     }
 
-    public async Task<(ShiftDetailDto? shift, string? error, bool isConflict)> UpdateShiftAsync(Guid id, UpdateShiftRequest request)
+    public async Task<(ShiftDetailDto? shift, string? error, bool isConflict)> UpdateShiftAsync(Guid id, UpdateShiftRequest request, string? currentExternalUserId = null)
     {
         var shift = await _context.Shifts.FindAsync(id);
 
@@ -182,6 +204,8 @@ public class ShiftService
             ss.SignedUpAt
         )).ToList();
 
+        var isSignedUp = currentExternalUserId != null && signupDtos.Any(s => s.ExternalUserId == currentExternalUserId);
+
         var dto = new ShiftDetailDto(
             shift.Id,
             shift.Title,
@@ -194,7 +218,8 @@ public class ShiftService
             shift.ClubId,
             shift.CreatedById,
             shift.CreatedAt,
-            shift.UpdatedAt
+            shift.UpdatedAt,
+            isSignedUp
         );
 
         return (dto, null, false);

backend/WorkClub.Api/Services/TaskService.cs

@@ -18,7 +18,7 @@ public class TaskService
         _tenantProvider = tenantProvider;
     }
 
-    public async Task<TaskListDto> GetTasksAsync(string? statusFilter, int page, int pageSize)
+    public async Task<TaskListDto> GetTasksAsync(string? statusFilter, int page, int pageSize, string? currentExternalUserId = null)
     {
         var query = _context.WorkItems.AsQueryable();
 
@@ -38,24 +38,45 @@ public class TaskService
             .Take(pageSize)
             .ToListAsync();
 
+        Guid? memberId = null;
+        if (currentExternalUserId != null)
+        {
+            var tenantId = _tenantProvider.GetTenantId();
+            memberId = await _context.Members
+                .Where(m => m.ExternalUserId == currentExternalUserId && m.TenantId == tenantId)
+                .Select(m => m.Id)
+                .FirstOrDefaultAsync();
+        }
+
         var itemDtos = items.Select(w => new TaskListItemDto(
             w.Id,
             w.Title,
             w.Status.ToString(),
             w.AssigneeId,
-            w.CreatedAt
+            w.CreatedAt,
+            memberId != null && w.AssigneeId == memberId
         )).ToList();
 
         return new TaskListDto(itemDtos, total, page, pageSize);
     }
 
-    public async Task<TaskDetailDto?> GetTaskByIdAsync(Guid id)
+    public async Task<TaskDetailDto?> GetTaskByIdAsync(Guid id, string? currentExternalUserId = null)
     {
         var workItem = await _context.WorkItems.FindAsync(id);
 
         if (workItem == null)
             return null;
 
+        Guid? memberId = null;
+        if (currentExternalUserId != null)
+        {
+            var tenantId = _tenantProvider.GetTenantId();
+            memberId = await _context.Members
+                .Where(m => m.ExternalUserId == currentExternalUserId && m.TenantId == tenantId)
+                .Select(m => m.Id)
+                .FirstOrDefaultAsync();
+        }
+
         return new TaskDetailDto(
             workItem.Id,
             workItem.Title,
@@ -66,7 +87,8 @@ public class TaskService
             workItem.ClubId,
             workItem.DueDate,
             workItem.CreatedAt,
-            workItem.UpdatedAt
+            workItem.UpdatedAt,
+            memberId != null && workItem.AssigneeId == memberId
         );
     }
 
@@ -102,13 +124,14 @@ public class TaskService
             workItem.ClubId,
             workItem.DueDate,
             workItem.CreatedAt,
-            workItem.UpdatedAt
+            workItem.UpdatedAt,
+            false
         );
 
         return (dto, null);
     }
 
-    public async Task<(TaskDetailDto? task, string? error, bool isConflict)> UpdateTaskAsync(Guid id, UpdateTaskRequest request)
+    public async Task<(TaskDetailDto? task, string? error, bool isConflict)> UpdateTaskAsync(Guid id, UpdateTaskRequest request, string? currentExternalUserId = null)
     {
         var workItem = await _context.WorkItems.FindAsync(id);
 
@@ -153,6 +176,16 @@ public class TaskService
             return (null, "Task was modified by another user. Please refresh and try again.", true);
         }
 
+        Guid? memberId = null;
+        if (currentExternalUserId != null)
+        {
+            var tenantId = _tenantProvider.GetTenantId();
+            memberId = await _context.Members
+                .Where(m => m.ExternalUserId == currentExternalUserId && m.TenantId == tenantId)
+                .Select(m => m.Id)
+                .FirstOrDefaultAsync();
+        }
+
         var dto = new TaskDetailDto(
             workItem.Id,
             workItem.Title,
@@ -163,7 +196,8 @@ public class TaskService
             workItem.ClubId,
             workItem.DueDate,
             workItem.CreatedAt,
-            workItem.UpdatedAt
+            workItem.UpdatedAt,
+            memberId != null && workItem.AssigneeId == memberId
         );
 
         return (dto, null, false);
@@ -181,4 +215,81 @@ public class TaskService
 
         return true;
     }
+
+    public async Task<(bool success, string? error)> AssignToMeAsync(Guid taskId, string externalUserId)
+    {
+        var tenantId = _tenantProvider.GetTenantId();
+        var memberId = await _context.Members
+            .Where(m => m.ExternalUserId == externalUserId && m.TenantId == tenantId)
+            .Select(m => m.Id)
+            .FirstOrDefaultAsync();
+
+        if (memberId == Guid.Empty)
+            return (false, "User is not a member of this club");
+
+        var workItem = await _context.WorkItems.FindAsync(taskId);
+        if (workItem == null)
+            return (false, "Task not found");
+
+        if (workItem.AssigneeId.HasValue)
+            return (false, "Task is already assigned");
+
+        workItem.AssigneeId = memberId;
+        
+        if (workItem.CanTransitionTo(WorkItemStatus.Assigned))
+            workItem.TransitionTo(WorkItemStatus.Assigned);
+
+        workItem.UpdatedAt = DateTimeOffset.UtcNow;
+        
+        try
+        {
+            await _context.SaveChangesAsync();
+        }
+        catch (DbUpdateConcurrencyException)
+        {
+            return (false, "Task was modified by another user");
+        }
+
+        return (true, null);
+    }
+
+    public async Task<(bool success, string? error)> UnassignFromMeAsync(Guid taskId, string externalUserId)
+    {
+        var tenantId = _tenantProvider.GetTenantId();
+        var memberId = await _context.Members
+            .Where(m => m.ExternalUserId == externalUserId && m.TenantId == tenantId)
+            .Select(m => m.Id)
+            .FirstOrDefaultAsync();
+
+        if (memberId == Guid.Empty)
+            return (false, "User is not a member of this club");
+
+        var workItem = await _context.WorkItems.FindAsync(taskId);
+        if (workItem == null)
+            return (false, "Task not found");
+
+        if (workItem.AssigneeId != memberId)
+            return (false, "Task is not assigned to you");
+
+        workItem.AssigneeId = null;
+
+        if (workItem.Status == WorkItemStatus.Assigned || workItem.Status == WorkItemStatus.InProgress)
+        {
+            // Transition back to open if no longer assigned and not marked Review/Done
+            workItem.Status = WorkItemStatus.Open;
+        }
+
+        workItem.UpdatedAt = DateTimeOffset.UtcNow;
+        
+        try
+        {
+            await _context.SaveChangesAsync();
+        }
+        catch (DbUpdateConcurrencyException)
+        {
+            return (false, "Task was modified by another user");
+        }
+
+        return (true, null);
+    }
 }

backend/WorkClub.Application/Shifts/DTOs/ShiftDetailDto.cs

@@ -12,7 +12,8 @@ public record ShiftDetailDto(
     Guid ClubId,
     Guid CreatedById,
     DateTimeOffset CreatedAt,
-    DateTimeOffset UpdatedAt
+    DateTimeOffset UpdatedAt,
+    bool IsSignedUp
 );
 
 public record ShiftSignupDto(

backend/WorkClub.Application/Shifts/DTOs/ShiftListDto.cs

@@ -13,5 +13,6 @@ public record ShiftListItemDto(
     DateTimeOffset StartTime,
     DateTimeOffset EndTime,
     int Capacity,
-    int CurrentSignups
+    int CurrentSignups,
+    bool IsSignedUp
 );

backend/WorkClub.Application/Tasks/DTOs/TaskDetailDto.cs

@@ -10,5 +10,6 @@ public record TaskDetailDto(
     Guid ClubId,
     DateTimeOffset? DueDate,
     DateTimeOffset CreatedAt,
-    DateTimeOffset UpdatedAt
+    DateTimeOffset UpdatedAt,
+    bool IsAssignedToMe
 );

backend/WorkClub.Application/Tasks/DTOs/TaskListDto.cs

@@ -12,5 +12,6 @@ public record TaskListItemDto(
     string Title,
     string Status,
     Guid? AssigneeId,
-    DateTimeOffset CreatedAt
+    DateTimeOffset CreatedAt,
+    bool IsAssignedToMe
 );

backend/WorkClub.Tests.Integration/Shifts/ShiftCrudTests.cs

@@ -198,9 +198,8 @@ public class ShiftCrudTests : IntegrationTestBase
     {
         // Arrange
         var shiftId = Guid.NewGuid();
-        var clubId = Guid.NewGuid();
+        var (clubId, memberId, externalUserId) = await SeedMemberAsync("tenant1", "member@test.com");
         var createdBy = Guid.NewGuid();
-        var memberId = Guid.NewGuid();
         var now = DateTimeOffset.UtcNow;
 
         using (var scope = Factory.Services.CreateScope())
@@ -236,7 +235,7 @@ public class ShiftCrudTests : IntegrationTestBase
         }
 
         SetTenant("tenant1");
-        AuthenticateAs("member@test.com", new Dictionary<string, string> { ["tenant1"] = "Member" });
+        AuthenticateAs("member@test.com", new Dictionary<string, string> { ["tenant1"] = "Member" }, externalUserId);
 
         // Act
         var response = await Client.GetAsync($"/api/shifts/{shiftId}");
@@ -707,6 +706,6 @@ public class ShiftCrudTests : IntegrationTestBase
 
 // Response DTOs for test assertions
 public record ShiftListResponse(List<ShiftListItemResponse> Items, int Total, int Page, int PageSize);
-public record ShiftListItemResponse(Guid Id, string Title, DateTimeOffset StartTime, DateTimeOffset EndTime, int Capacity, int CurrentSignups);
+public record ShiftListItemResponse(Guid Id, string Title, DateTimeOffset StartTime, DateTimeOffset EndTime, int Capacity, int CurrentSignups, bool IsSignedUp);
 public record ShiftDetailResponse(Guid Id, string Title, string? Description, string? Location, DateTimeOffset StartTime, DateTimeOffset EndTime, int Capacity, List<ShiftSignupResponse> Signups, Guid ClubId, Guid CreatedById, DateTimeOffset CreatedAt, DateTimeOffset UpdatedAt);
 public record ShiftSignupResponse(Guid Id, Guid MemberId, DateTimeOffset SignedUpAt);

frontend/src/app/(protected)/shifts/[id]/page.tsx

@@ -23,7 +23,7 @@ export default function ShiftDetailPage({ params }: { params: Promise<{ id: stri
   const capacityPercentage = (shift.signups.length / shift.capacity) * 100;
   const isFull = shift.signups.length >= shift.capacity;
   const isPast = new Date(shift.startTime) < new Date();
-  const isSignedUp = shift.signups.some((s) => s.memberId === session?.user?.id || s.externalUserId === session?.user?.id);
+  const isSignedUp = shift.isSignedUp;
 
   const handleSignUp = async () => {
     await signUpMutation.mutateAsync(shift.id);

frontend/src/app/(protected)/tasks/[id]/page.tsx

@@ -2,7 +2,7 @@
 
 import { use } from 'react';
 import Link from 'next/link';
-import { useTask, useUpdateTask } from '@/hooks/useTasks';
+import { useTask, useUpdateTask, useAssignTask, useUnassignTask } from '@/hooks/useTasks';
 import { Button } from '@/components/ui/button';
 import { Badge } from '@/components/ui/badge';
 import { Card, CardContent, CardDescription, CardHeader, CardTitle } from '@/components/ui/card';
@@ -26,9 +26,13 @@ const statusColors: Record<string, string> = {
 export default function TaskDetailPage({ params }: { params: Promise<{ id: string }> }) {
   const resolvedParams = use(params);
   const { data: task, isLoading, error } = useTask(resolvedParams.id);
-  const { mutate: updateTask, isPending } = useUpdateTask();
+  const { mutate: updateTask, isPending: isUpdating } = useUpdateTask();
+  const { mutate: assignTask, isPending: isAssigning } = useAssignTask();
+  const { mutate: unassignTask, isPending: isUnassigning } = useUnassignTask();
   const { data: session } = useSession();
 
+  const isPending = isUpdating || isAssigning || isUnassigning;
+
   if (isLoading) return <div className="p-8">Loading task...</div>;
   if (error || !task) return <div className="p-8 text-red-500">Failed to load task.</div>;
 
@@ -39,9 +43,11 @@ export default function TaskDetailPage({ params }: { params: Promise<{ id: strin
   };
 
   const handleAssignToMe = () => {
-    if (session?.user?.id) {
+    assignTask(task.id);
-      updateTask({ id: task.id, data: { assigneeId: session.user.id } });
+  };
-    }
+
+  const handleUnassign = () => {
+    unassignTask(task.id);
   };
 
   const getTransitionLabel = (status: string, newStatus: string) => {
@@ -107,7 +113,16 @@ export default function TaskDetailPage({ params }: { params: Promise<{ id: strin
                     disabled={isPending}
                     variant="outline"
                   >
-                    {isPending ? 'Assigning...' : 'Assign to Me'}
+                    {isAssigning ? 'Assigning...' : 'Assign to Me'}
+                  </Button>
+                )}
+                {task.isAssignedToMe && (
+                  <Button
+                    onClick={handleUnassign}
+                    disabled={isPending}
+                    variant="outline"
+                  >
+                    {isUnassigning ? 'Unassigning...' : 'Unassign'}
                   </Button>
                 )}
                 {validTransitions.map((nextStatus) => (

frontend/src/components/__tests__/shift-card.test.tsx

@@ -1,8 +1,23 @@
-import { describe, it, expect } from 'vitest';
+import { describe, it, expect, vi, beforeEach } from 'vitest';
 import { render, screen } from '@testing-library/react';
 import { ShiftCard } from '../shifts/shift-card';
+import { useSignUpShift, useCancelSignUp } from '@/hooks/useShifts';
+
+vi.mock('@/hooks/useShifts', () => ({
+  useSignUpShift: vi.fn(),
+  useCancelSignUp: vi.fn(),
+}));
 
 describe('ShiftCard', () => {
+  const mockSignUp = vi.fn();
+  const mockCancel = vi.fn();
+
+  beforeEach(() => {
+    vi.clearAllMocks();
+    (useSignUpShift as ReturnType<typeof vi.fn>).mockReturnValue({ mutate: mockSignUp, isPending: false });
+    (useCancelSignUp as ReturnType<typeof vi.fn>).mockReturnValue({ mutate: mockCancel, isPending: false });
+  });
+
   it('shows capacity correctly (2/3 spots filled)', () => {
     render(
       <ShiftCard
@@ -13,6 +28,7 @@ describe('ShiftCard', () => {
           endTime: new Date(Date.now() + 200000).toISOString(),
           capacity: 3,
           currentSignups: 2,
+          isSignedUp: false,
         }}
       />
     );
@@ -29,6 +45,7 @@ describe('ShiftCard', () => {
           endTime: new Date(Date.now() + 200000).toISOString(),
           capacity: 3,
           currentSignups: 3,
+          isSignedUp: false,
         }}
       />
     );
@@ -46,10 +63,28 @@ describe('ShiftCard', () => {
           endTime: new Date(Date.now() - 100000).toISOString(),
           capacity: 3,
           currentSignups: 1,
+          isSignedUp: false,
         }}
       />
     );
     expect(screen.getByText('Past')).toBeInTheDocument();
     expect(screen.queryByRole('button', { name: 'Sign Up' })).not.toBeInTheDocument();
   });
+
+  it('shows cancel sign-up button when signed up', () => {
+    render(
+      <ShiftCard
+        shift={{
+          id: '1',
+          title: 'Signed Up Shift',
+          startTime: new Date(Date.now() + 100000).toISOString(),
+          endTime: new Date(Date.now() + 200000).toISOString(),
+          capacity: 3,
+          currentSignups: 1,
+          isSignedUp: true,
+        }}
+      />
+    );
+    expect(screen.getByText('Cancel Sign-up')).toBeInTheDocument();
+  });
 });

frontend/src/components/__tests__/shift-detail.test.tsx

@@ -51,6 +51,7 @@ describe('ShiftDetailPage', () => {
         endTime: new Date(Date.now() + 200000).toISOString(),
         capacity: 3,
         signups: [{ id: 's1', memberId: 'other-user' }],
+        isSignedUp: false,
       },
       isLoading: false,
     });
@@ -77,6 +78,7 @@ describe('ShiftDetailPage', () => {
         endTime: new Date(Date.now() + 200000).toISOString(),
         capacity: 3,
         signups: [{ id: 's1', memberId: 'user-123' }],
+        isSignedUp: true,
       },
       isLoading: false,
     });
@@ -103,6 +105,7 @@ describe('ShiftDetailPage', () => {
         endTime: new Date(Date.now() + 200000).toISOString(),
         capacity: 3,
         signups: [],
+        isSignedUp: false,
       },
       isLoading: false,
     });

frontend/src/components/__tests__/task-detail.test.tsx

@@ -1,7 +1,7 @@
 import { render, screen, act } from '@testing-library/react';
 import { describe, it, expect, vi, beforeEach } from 'vitest';
 import TaskDetailPage from '@/app/(protected)/tasks/[id]/page';
-import { useTask, useUpdateTask } from '@/hooks/useTasks';
+import { useTask, useUpdateTask, useAssignTask, useUnassignTask } from '@/hooks/useTasks';
 
 vi.mock('next/navigation', () => ({
   useRouter: vi.fn(() => ({
@@ -21,21 +21,34 @@ vi.mock('next-auth/react', () => ({
 vi.mock('@/hooks/useTasks', () => ({
   useTask: vi.fn(),
   useUpdateTask: vi.fn(),
+  useAssignTask: vi.fn(),
+  useUnassignTask: vi.fn(),
 }));
 
 describe('TaskDetailPage', () => {
-  const mockMutate = vi.fn();
+  const mockUpdate = vi.fn();
+  const mockAssign = vi.fn();
+  const mockUnassign = vi.fn();
 
   beforeEach(() => {
+    vi.clearAllMocks();
     (useUpdateTask as ReturnType<typeof vi.fn>).mockReturnValue({
-      mutate: mockMutate,
+      mutate: mockUpdate,
+      isPending: false,
+    });
+    (useAssignTask as ReturnType<typeof vi.fn>).mockReturnValue({
+      mutate: mockAssign,
+      isPending: false,
+    });
+    (useUnassignTask as ReturnType<typeof vi.fn>).mockReturnValue({
+      mutate: mockUnassign,
       isPending: false,
     });
   });
 
   it('shows valid transitions for Open status', async () => {
     (useTask as ReturnType<typeof vi.fn>).mockReturnValue({
-      data: { id: '1', title: 'Task 1', status: 'Open', description: 'Desc', createdAt: '2024-01-01', updatedAt: '2024-01-01' },
+      data: { id: '1', title: 'Task 1', status: 'Open', description: 'Desc', createdAt: '2024-01-01', updatedAt: '2024-01-01', isAssignedToMe: false },
       isLoading: false,
       error: null,
     });
@@ -52,7 +65,7 @@ describe('TaskDetailPage', () => {
 
   it('shows valid transitions for InProgress status', async () => {
     (useTask as ReturnType<typeof vi.fn>).mockReturnValue({
-      data: { id: '1', title: 'Task 1', status: 'InProgress', description: 'Desc', createdAt: '2024-01-01', updatedAt: '2024-01-01' },
+      data: { id: '1', title: 'Task 1', status: 'InProgress', description: 'Desc', createdAt: '2024-01-01', updatedAt: '2024-01-01', isAssignedToMe: false },
       isLoading: false,
       error: null,
     });
@@ -68,7 +81,7 @@ describe('TaskDetailPage', () => {
 
   it('shows valid transitions for Review status (including back transition)', async () => {
     (useTask as ReturnType<typeof vi.fn>).mockReturnValue({
-      data: { id: '1', title: 'Task 1', status: 'Review', description: 'Desc', createdAt: '2024-01-01', updatedAt: '2024-01-01' },
+      data: { id: '1', title: 'Task 1', status: 'Review', description: 'Desc', createdAt: '2024-01-01', updatedAt: '2024-01-01', isAssignedToMe: false },
       isLoading: false,
       error: null,
     });
@@ -91,7 +104,8 @@ describe('TaskDetailPage', () => {
         assigneeId: null,
         description: 'Desc', 
         createdAt: '2024-01-01', 
-        updatedAt: '2024-01-01' 
+        updatedAt: '2024-01-01',
+        isAssignedToMe: false
       },
       isLoading: false,
       error: null,
@@ -105,8 +119,7 @@ describe('TaskDetailPage', () => {
     expect(screen.getByText('Assign to Me')).toBeInTheDocument();
   });
 
-  it('calls updateTask with assigneeId when Assign to Me clicked', async () => {
+  it('calls assignTask with task id when Assign to Me clicked', async () => {
-    const mockMutate = vi.fn();
     (useTask as ReturnType<typeof vi.fn>).mockReturnValue({
       data: { 
         id: '1', 
@@ -115,15 +128,12 @@ describe('TaskDetailPage', () => {
         assigneeId: null,
         description: 'Desc', 
         createdAt: '2024-01-01', 
-        updatedAt: '2024-01-01' 
+        updatedAt: '2024-01-01',
+        isAssignedToMe: false
       },
       isLoading: false,
       error: null,
     });
-    (useUpdateTask as ReturnType<typeof vi.fn>).mockReturnValue({
-      mutate: mockMutate,
-      isPending: false,
-    });
 
     const params = Promise.resolve({ id: '1' });
     await act(async () => {
@@ -135,9 +145,37 @@ describe('TaskDetailPage', () => {
       button.click();
     });
 
-    expect(mockMutate).toHaveBeenCalledWith({
+    expect(mockAssign).toHaveBeenCalledWith('1');
-      id: '1',
-      data: { assigneeId: 'user-123' },
   });
+
+  it('renders Unassign button and calls unassignTask when clicked', async () => {
+    (useTask as ReturnType<typeof vi.fn>).mockReturnValue({
+      data: { 
+        id: '1', 
+        title: 'Task 1', 
+        status: 'Assigned', 
+        assigneeId: 'some-member-id',
+        description: 'Desc', 
+        createdAt: '2024-01-01', 
+        updatedAt: '2024-01-01',
+        isAssignedToMe: true
+      },
+      isLoading: false,
+      error: null,
+    });
+
+    const params = Promise.resolve({ id: '1' });
+    await act(async () => {
+      render(<TaskDetailPage params={params} />);
+    });
+
+    const button = screen.getByText('Unassign');
+    expect(button).toBeInTheDocument();
+    
+    await act(async () => {
+      button.click();
+    });
+
+    expect(mockUnassign).toHaveBeenCalledWith('1');
   });
 });

frontend/src/components/shifts/shift-card.tsx

@@ -3,13 +3,16 @@ import { Card, CardHeader, CardTitle, CardDescription, CardContent } from '@/com
 import { Button } from '@/components/ui/button';
 import { Progress } from '@/components/ui/progress';
 import { Badge } from '@/components/ui/badge';
-import { ShiftListItemDto } from '@/hooks/useShifts';
+import { ShiftListItemDto, useSignUpShift, useCancelSignUp } from '@/hooks/useShifts';
 
 interface ShiftCardProps {
   shift: ShiftListItemDto;
 }
 
 export function ShiftCard({ shift }: ShiftCardProps) {
+  const signUpMutation = useSignUpShift();
+  const cancelMutation = useCancelSignUp();
+
   const capacityPercentage = (shift.currentSignups / shift.capacity) * 100;
   const isFull = shift.currentSignups >= shift.capacity;
   const isPast = new Date(shift.startTime) < new Date();
@@ -39,8 +42,15 @@ export function ShiftCard({ shift }: ShiftCardProps) {
             <Link href={`/shifts/${shift.id}`}>
               <Button variant="outline" size="sm">View Details</Button>
             </Link>
-            {!isPast && !isFull && (
+            {!isPast && !isFull && !shift.isSignedUp && (
-              <Button size="sm">Sign Up</Button>
+              <Button size="sm" onClick={() => signUpMutation.mutate(shift.id)} disabled={signUpMutation.isPending}>
+                {signUpMutation.isPending ? 'Signing up...' : 'Sign Up'}
+              </Button>
+            )}
+            {!isPast && shift.isSignedUp && (
+              <Button variant="outline" size="sm" onClick={() => cancelMutation.mutate(shift.id)} disabled={cancelMutation.isPending}>
+                {cancelMutation.isPending ? 'Canceling...' : 'Cancel Sign-up'}
+              </Button>
             )}
           </div>
         </div>

frontend/src/hooks/useShifts.ts

@@ -16,6 +16,7 @@ export interface ShiftListItemDto {
   endTime: string;
   capacity: number;
   currentSignups: number;
+  isSignedUp: boolean;
 }
 
 export interface ShiftDetailDto {
@@ -31,6 +32,7 @@ export interface ShiftDetailDto {
   createdById: string;
   createdAt: string;
   updatedAt: string;
+  isSignedUp: boolean;
 }
 
 export interface ShiftSignupDto {

frontend/src/hooks/useTasks.ts

@@ -11,10 +11,9 @@ export interface TaskListDto {
 
 export interface TaskListItemDto {
   id: string;
-  title: string;
-  status: string;
   assigneeId: string | null;
   createdAt: string;
+  isAssignedToMe: boolean;
 }
 
 export interface TaskDetailDto {
@@ -28,6 +27,7 @@ export interface TaskDetailDto {
   dueDate: string | null;
   createdAt: string;
   updatedAt: string;
+  isAssignedToMe: boolean;
 }
 
 export interface CreateTaskRequest {
@@ -120,3 +120,41 @@ export function useUpdateTask() {
     },
   });
 }
+
+export function useAssignTask() {
+  const queryClient = useQueryClient();
+  const { activeClubId } = useTenant();
+  
+  return useMutation({
+    mutationFn: async (id: string) => {
+      const res = await apiClient(`/api/tasks/${id}/assign`, {
+        method: 'POST',
+      });
+      if (!res.ok) throw new Error('Failed to assign task');
+      return res;
+    },
+    onSuccess: (_, id) => {
+      queryClient.invalidateQueries({ queryKey: ['tasks', activeClubId] });
+      queryClient.invalidateQueries({ queryKey: ['tasks', activeClubId, id] });
+    },
+  });
+}
+
+export function useUnassignTask() {
+  const queryClient = useQueryClient();
+  const { activeClubId } = useTenant();
+  
+  return useMutation({
+    mutationFn: async (id: string) => {
+      const res = await apiClient(`/api/tasks/${id}/assign`, {
+        method: 'DELETE',
+      });
+      if (!res.ok) throw new Error('Failed to unassign task');
+      return res;
+    },
+    onSuccess: (_, id) => {
+      queryClient.invalidateQueries({ queryKey: ['tasks', activeClubId] });
+      queryClient.invalidateQueries({ queryKey: ['tasks', activeClubId, id] });
+    },
+  });
+}